NITRO-EXPLOSIVES.
UNIVERSITY
OF
NlTRO-EXFLOSIVES
A PRACTICAL TREATISE
CONCERNING THE
PROPERTIES, MANUFACTURE, AND ANALYSIS OF
NITRATED SUBSTANCES, INCLUDING THE FULMINATES,
SMOKELESS POWDERS, AND CELLULOID
BY
P. GERALD SANFORD, F.I.C., F.C.S.
Member of the Society of Public Analysts ; Consulting Chemist to the Cotton Powder Company Limited ; late Resident Chemist at the Guncotton Works, Stoivmarket, and the Dynamite Works, Hayle, Cornwall
LONDON CROSBY LOCKWOOD AND SON
7 STATIONERS' HALL COURT, LUDGATE HILL 1896.
O
I
Printed at THE DARIEN PRESS, Edinburgh.
To MY FATHER, As A TOKEN OF AFFECTION AND RESPECT.
€.fcSE OF THE IVERSITY/
€SE OF THE VERSITY lUF
PREFACE
T N compiling the following treatise, my aim has ** been to give a brief but thoroughly prac- tical account of the properties, manufacture, and methods of analysis of the various nitro-explosives now so largely used for mining and blasting pur- poses and as propulsive agents ; and it is believed that the account given of the manufacture of nitro- glycerine and of the gelatine dynamites will be found more complete than in any similar work yet published in this country.
For many of the facts and figures contained in the chapter on Smokeless Powders I am indebted to (amongst others) the late Mr J. D. Dougall and Messrs A. C. Ponsonby and H. M. Chapman, F.C.S. ; and for details with regard to Roburite to Messrs H. A. Krohn and W. J. Orsman, F.I.C. To these gentlemen my cordial thanks are due. Among the authorities which have been consulted in the general preparation of the work
Vlll PREFACE.
may be mentioned the Journals of the Chemical Society, the Society of Chemical Industry, the United States Naval Institute, and the Royal Artillery Institution. I have also referred to several volumes of the periodical publication Arms and Explosives; to various papers by Sir Frederick Abel, Bart., F.R.S., and General Wardell, R.A., on Gun - Cotton ; to ''Modern Artillery," by Capt. Lloyd, R.N., and A. G. Hadcock, R.A. ; to the late Colonel Cundill's "Dictionary of Explosives"; as well as to the works of Messrs Eissler, Berthelot, and others.
The illustrations have been prepared chiefly from my own drawings. A few, however, have been taken (by permission) from the pages of Arms and Explosives, or from other sources which are acknowledged in the text.
P. G. S.
THE LABORATORY,
20 CULLUM STREET, E.G., May 1896.
TABLE OF CONTENTS.
CHAPTER I.— INTRODUCTION.
PAGE
The Nitro-Explosives — Substances that have been Nitrated — The Danger Area — Systems of Professors Lodge, Zenger, and Melsens for the Protection of Buildings from Lightning, &c. - 1-18
CHAPTER II.— NITRO-GLYCERINE.
Properties of Nitro-Glycerine — Manufacture — Nitration — Separa- tion—Washing and Filtering — Drying, Storing, &c. — The Waste Acids— Nitric Acid Plants - 19-42
CHAPTER III.— DYNAMITE.
Kieselguhr Dynamite — Classification of Dynamites — Properties and Efficiency of Ordinary Dynamite — Other Forms of Dynamite — Gelatine and Gelatine Dynamites, Suitable Gun- Cotton for, and Treatment of — Other Materials Used — Com- position of Gelignite — Blasting Gelatine— Gelatine Dynamite — Absorbing Materials — Wood Pulp — Potassium Nitrate, &c. — Manufacture, &c. — Apparatus Used — The Properties of the Gelatine Compounds — Cordite — Composition and Manufacture 43-66
CHAPTER IV.— NITRO-CELLULOSE, &c.
Cellulose— Properties— Discovery of Gun-Cotton—Properties of Gun-Cottons—Varieties of — Soluble and Insoluble Gun- Cottons — Manufacture of Gun-Cotton — Dipping and Steep- ing— Whirling Out the Acid — Washing, Boiling, Pulping, Compressing — The Waltham Abbey Process — Le Bouchet Process — Granulation of Gun-Cotton — Collodion-Cotton — Manufacture — Acid Mixture Used — Cotton Used, &c. — Nitrated Gun-Cotton — Tonite — Dangers in Manufacture of Gun-Cotton — Trench's Fire-Extinguishing Compound — Uses of Collodion-Cotton — Celluloid — Manufacture, £c. — Nitro- Starch, Nitro-Jute, and Nitro-Mannite 67-129
b
X TABLE OF CONTENTS.
PAGE
CHAPTER V.— NITRO-BENZOL, ROBURITE, BELLITE, PICRIC ACID, &c.
Explosives derived from Benzene — Toluene, Nitro-Benzene, Di- and Tri-Nitro — Roburite : Properties and Manufacture — Bellite: Properties, &c.— Securite — Tonite No. 3— Nitro- Toluene — Nitro - Naphthalene — Ammonite — Sprengel's Explosives — Picric Acid — Picrates — Picric Powders — Melinite — Abel's Mixture — Brugere's Powders. THE FULMINATES.
Composition, Formula, Preparation, Danger of, &c. — Detonators :
Sizes, Composition, Manufacture — Fuses, &c. - - - 130-164
CHAPTER VI.— SMOKELESS POWDERS IN GENERAL.
Cordite — Ballistite — Schultze's E.G. Powder— J.B. Powder— Indurite — Vielle Poudre — Rifleite — Cannonite — Walsrode and Coopaal Powders — Amberite — Troisdorf — Maximite — Picric A*Cid Powders, &c. &c. ------- 165-191
CHAPTER VII.— ANALYSIS OF EXPLOSIVES.
Kieselguhr Dynamite — Gelatine Compounds — Tonite — Cordite — Vaseline — Acetone — Allen's Scheme for Analysis of Ex- plosives — Nitro-Cotton — Solubility Test — Non- Nitrated Cotton — Alkalinity — Ash and Inorganic Matter — Deter- mination of Nitrogen — Lunge, Champion and Pellet's, Schultze- Tieman, and Kjeldahl's Methods — Celluloid — Picric Acid and Picrates — Resinous and Tarry Matters — Sulphuric Acid and Hydrochloric Acid and Oxalic Acid — Nitric Acid — Inorganic Impurities— General Impurities and Adulterations — Potassium Picrate, &c. — Picrates of the Alkaloids — Analysis of Glycerine— Residue— Silver Test — Nitration Total Acid Equivalent — Neutrality — Free Fatty Acids — Combined Fatty Acids — Impurities — Oleic Acid — Sodium Chloride — Determination of Glycerine — Waste Acids — Sodium Nitrate — Mercury Fulminate — Table for Correction of Volumes of Gases, for Temperature and Pressure - - - - 192-231
CHAPTER VIII.— FIRING POINT OF EXPLOSIVES. Horsley's Apparatus — Table of Firing Points — The Government Heat Test — Apparatus, &c., for Dynamites, Nitro-Glycerine, Nitro-Cotton, and Smokeless Powders — Liquefaction and Exudation Tests— Page's Regulator for Heat Test Apparatus- Specific Gravities of Explosives — Table of Temperature of Detonation, Sensitiveness, &c. 232-245
TABLE OF CONTENTS. xi
PAGE
CHAPTER IX.— THE DETERMINATION OF THE RELATIVE STRENGTH OF EXPLOSIVES.
Effectiveness of an Explosive — High and Low Explosives — Theo- retical Efficiency — MM. Roux and Sarrau's Results — Abel and Noble's — Nobel's Ballistic Test — The Mortar — Pressure or Crusher Gauge — Lead Cylinders — The Foot-Pounds Machine — Noble's Pressure Gauge— Lieut. Walke's Results— Calcula- tion of Pressure Developed by Dynamite and Gun- Cotton — M'Nab's and Ristori's Results of Heat Developed by the Ex- plosion of Various Explosives— Composition of some of the Explosives in Common Use — Blasting, &c. - 246-264
INDEX 265-270
LIST OF ILLUSTRATIONS.
.
FRONTISPIECE — Danger Building showing Protecting Mounds.
1. Section of Nitro-Glycerine Conduit 7
2. Melsens System of Lightning Conductors - 1 1
3. French System 12
40 & 4$. English Government System - - 13
5. Upper Portion of Nitrator for Nitro-Glycerine - 27
6. Small Nitrator - - 31
7. Nitro-Glycerine Separator ----- 32
8. Nitro-Glycerine Filtering Apparatus - - 34 ga & 9^. Messrs Werner & Pfleiderer's Mixing Machine 57
loa. M' Roberts' Mixing Machine for Blasting Gelatine - 58
106. Plan of same 59
11. Cartridge Machine for Gelatines 61
12. Cotton- Waste Drier - - - - - 79
13. Dipping Tank - 81
14. Hydro-Extractor or Centrifugal Drier - 82
15. Steeping Pot for Gun- Cotton - - 83 i6a & \6b. Gun-Cotton Beater 85
Xll LIST OF ILLUSTRATIONS.
FIG. PAGE
Ija. Poacher for Pulping Gun-Cotton 86
l*jb. Plan of same - 87
ijc. Another Form of Poacher - 87
1 8. Trench's Safety Cartridge - 104
19. Vessel used in Nitrating Paper - - - 113
20. Cage ditto — White & Schupphous' Apparatus 113
21. Do. Do. Do. 113 22a&22b. Nitrating Pot for Celluloid - 114
23. Plunge Tank - 114
24. Cartridge Fitted with Fuse and Detonator - 163
25. Gun-Cotton Primer - 164
26. Electric Firing Apparatus - - 164
27. Curve showing relation between Pressures of Cordite and Black
Powder, by Professor Vivian Lewes 170
28. Target Shot with Rifleite - - 177
29. Bullets do. 178
30. Lunge's Nitrometer 207
31. Modified do. 210
32. Horn's Nitrometer 210
33#. Schultze-Tieman Apparatus for Determination of Nitrogen in
Gun-Cotton 213
33(5. Decomposition Flask for Schultze-Tieman Method - - - 214
34. Abel's Heat Test Apparatus 234
35. Apparatus for Separation of Nitro-Glycerine from Dynamite - 237
36. Test Tube arranged for Heat Test .... . 238 370. Page's Regulator .... • '-. . 242 37/5. Do. showing Bye-Pass and Cut-off Arrangement - 243
38. Dynamite Mortar 249
390. Quinan's Pressure Gauge - - - - - - - - 251
39$. Steel Punch and Lead Cylinder for Use with Pressure Gauge - 2^1
40. Micrometer Calipers for Measuring Thickness of Lead Cylinders 252
41. Section of Lead Cylinders before and after Explosion - - 254
42. Noble's Pressure Gauge - - - - - - - - 254
43. Crusher Gauge - 256
NITRO-EXPLOSIVES.
CHAPTER I. INTRO D UCTOR K
The Nitro-Explosives — Substances that have been Nitrated — The Danger Area — Systems of Professors Lodge, Zenger, and Melsens for the Protection of Buildings from Lightning, &c.
THE manufacture of the various nitro-explosives has made great advances during late years, and the various forms of nitro compounds are gradually replacing the older forms of explosives, both for blasting purposes and also as propulsive agents, under the form of smokeless powders. The nitro-explosives belong to the so-called"^ High Explosives, and may be defined as any chemical compound possessed of explosive properties, or capable of combining with metals to form an explosive com- pound, which is produced by the chemical action of nitric acid, either alone or mixed with sulphuric acid, upon any carbonaceous substance, whether such com- pound is mechanically mixed with other substances or not*
The number of compounds and mixtures included under this definition is very large, and they are of very
* Definition given in Order of Council, No, i, Explosives Act,
1875-
A
2 NITRO-EXPLOSIVES.
different chemical composition. Among the substances that have been nitrated are : — Cellulose, under various forms, e.g.y cotton, lignin, &c. ; glycerine, benzene, starch, jute, sugar, phenol, wood, straw, and even such sub- stances as treacle and horse-dung. Some of these are fnot made upon the large scale, others are but little used, i Those of most importance are nitro-glycerine and nitro- cellulose. The former enters into the composition of all dynamites, and several smokeless powders ; and the second includes gun-cotton, collodion-cotton, nitrated wood, and the majority of the smokeless powders, which consist generally of nitro-cotton, nitro-lignin, nitro-jute, &c., &c., together with metallic nitrates, or nitro- glycerine.
The nitro-explosives consist generally of some organic substance in which the NO2 group, known as nitryl, has been substituted in place of hydrogen.
(OH
Thus in glycerine, C3H5-< OH, which is a trihydric
(OH
alcohol, and which occurs very widely distributed as the alcoholic or basic constituent of fats, the hydrogen atoms are replaced by the NO2 group, to form the highly explosive compound, nitro-glycerine. If one atom only is thus displaced, the mono-nitrate is formed
( ON02 thus, C3H5x OH ; and if the three atoms are displaced,
(OH
C3H5(ONO2)3, or the tri-nitrate, is formed, which is com- mercial nitro-glycerine. •
Another class, the nitro-celluloscs, are formed from cellulose, C6H10O5, which forms the groundwork of all vegetable tissues. Cellulose has some of the properties
NITRO COMPOUNDS IN GENERAL. 3;
of the alcohols, and forms etherial salts when treated with nitric and sulphuric acids. The hexa-nitrate, or gun-cotton, has the formula, C12H14O4(ONO2)6 ; and collodion-cotton, pyroxylin, &c., form the lower nitrates, i.e., the tetra- and penta-nitrates. These last are soluble in various solvents, such as ether-alcohol and nitro- glycerine, in which the hexa-nitrate is insoluble. They all dissolve, however, in acetone and acetic ether.
The solution of the soluble varieties in ether-alcohol is known as collodion, which finds many applications in the arts. The hydrocarbon benzene, C6H0, prepared from the light oil obtained from coal-tar, when nitrated forms nitro - benzenes, such as mono - nitro - benzene, C6H5NO2, and di-nitro-benzene, C6H4(NO2)2, in which one and two atoms are replaced by the NO2 group. The latter of these compounds is used as an explosive, and enters into the composition of such well-known explo- sives as roburite, &c. The presence of nitro groups in a f substance increases the difficulty of further nitration, and j in any case not more than three nitro groups can be introduced into an aromatic compound, or the phenols. All aromatic compounds with the general formula, CGH4X2, give, however, three series. They are called ortho, meta, or para compounds, depending upon the position of the NO2 groups introduced.
Certain regularities have been observed in the forma- tion of nitro compounds. If, for example, a substance contains alkyl or hydroxyl groups, large quantities of the para compound arc obtained, and very little of the ortho. The substitution takes place, however, almost entirely in the meta position, if a nitro, carboxyl, or aldehyde group be present. Ordinary phenol, C6H5.OH, gives para- and ortho-nitro-phenol ; toluene gives para- and ortho-nitro-toluene ; but nitro-benzene forms meta-
4 NITRO-EXPLOSIVES.
di-nitro-benzene and benzoic acid, meta-nitro-benzoic acid.*
If the graphic formula of benzene be represented
H.I
C N02
H.CX CH.2
H.C CH.3
META-DINITRO -BENZENE H.4 No2>
N? I..
thus (No. i), then the positions I and 2 represent the ortho, i and 3 the meta, and I and 4 the para com- pounds. When the body phenol, C6H5.OH, is nitrated, a compound is formed known as tri-nitro-phenol, or picric acid, C6H2(NO2)3OH, which is used very exten- sively as an explosive, both as picric acid and in the form of picrates. Another nitro body that is used as an explosive is nitre-naphthalene, C10H6(NO2)2, in roburite, securite, and other explosives of this class. The hexa- nitro-mannite, C6H8(ONO2)6, is formed by treating a substance known as mannite, C6H8(OH)6, an alcohol formed by the lactic acid fermentation of sugar and closely related to the sugars, with nitric and sulphuric acids. It is a solid substance, and very explosive ; it contains 18.58 per cent, of nitrogen.
Nitro-starch has also been used for the manufacture of an explosive. Miihlhauer has described (Ding. Poly.
* "Organic Chemistry," Prof. Hjelt. Translated by J. B. Tingle, Ph.D.
NITRO-JUTE AND NITRO-STARCII. 5
Jour., 73, 137-143) three nitric ethers of starch, the tetra- nitro-starch, C12H16O6(ONO2)4, the penta- and hexa- nitro-starch. They are formed by acting upon potato starch dried at 100° C. with a mixture of nitric and sulphuric acids at a temperature of 20° to 25° C. Rice starch has also been used in its production. Miihlhauer proposes to use this body as a smokeless powder, and to nitrate it with the spent mixed acids from the manufac- ture of nitro-glycerine. This substance contains from 10.96 to 11.09 Per cent of nitrogen. It is a white substance, very stable and soluble even in cold nitro- glycerine.
The explosive bodies formed by the nitration of jute have been studied by Messrs Cross and Bevan, and also by Miihlhauer. The former chemists give jute the formula C12H18O9, and believe that its conversion into a nitro compound takes place according to the equation —
This is equivalent to a gain in weight of 44 per cent, for the tri-nitrate, and 58 per cent, for the tetra-nitrate. The formation of the tetra-nitrate appears to be the limit of nitration of jute fibre. Messrs Cross and Bevan say, " In other words, if we represent the ligno-cellulose mole- cule by a C12 formula, it will contain four hydroxyl (OH) groups, or two less than cellulose similarly represented." It contains 11.5 per cent of nitrogen. * The jute nitrates resemble those of cellulose, and are in all essential points nitrates of ligno-cellulose.
Nitro-jute is used in the composition of the well- known Coopaal Smokeless Powders. Cross and Bevan are of opinion that there is no very obvious advantage in the use of lignified textile fibres as raw materials for explosive nitrates, seeing that a number ofjraw materials
tfNIVBBSIl
6 NITRO-EXPLOSIVES.
containing cellulose (chiefly as cotton) can be obtained at from £10 to ^25 a ton, and yield also 150 to 170 per cent of explosive material when nitrated (whereas jute only gives 154.4 Per cent.), and are in many ways superior to the products obtained from jute. Nitro- lignin, or nitrated wood, is, however, largely used in the composition of a good many of the smokeless powders, such as Schultze's, the Smokeless Powder Co.'s products, and others.
The Danger Area. — That portion of the works that is devoted to the actual manufacture or mixing of ex- plosive material is generally designated by the term " danger area," and the buildings erected upon it are spoken of as " danger buildings." The best material of which to construct these buildings is of wood, as in the event of an explosion they will offer less resistance, and will cause much less danger than brick or stone buildings. When an explosion of nitro-glycerine or dynamite occurs in one of these buildings, the sides are generally blown out, and the roof is raised some considerable height, and finally descends upon the blown-out sides. If, on the other hand, the same explosion had occurred in a strong brick or stone building, the walls of which would offer a much larger resistance, large pieces of brickwork would pro- bably have been thrown for a considerable distance, and have caused serious damage to surrounding buildings.
It is also a very good plan to surround all danger buildings with mounds of sand or earth, which should be covered with turf, and of such a height as to be above the roof of the buildings that they are intended to pro- tect (see frontispiece). These mounds are of great value in confining the force of the explosion, and the sides of the buildings being thrown against them are prevented
ARRANGEMENT OF THE DANGER AREA. f
from travelling any distance. In gunpowder works it is not unusual to surround the danger buildings with trees or dense underwood instead of mounds. This would be of no use in checking the force of explosion of the high explosives, but has been found a very useful precaution in the case of gunpowder.
In Great Britain it is necessary that all danger buildings should be a specified distance apart ; a license also must be obtained for each building. The applica- tion for a license must give a plan (drawn to scale) of the proposed factory or magazine, and the site, its bound- aries, and surroundings, and distance the building will be from any other buildings or works, &c., also the character, and construction of all the mounds, and nature of the processes to be carried on in the factory or building.*
The selection of a site for the danger area requires some attention. The purpose for which it is required, that is, the kind of explosive that it is intended to manu- facture, must be taken into consideration. A perfectly
FIG. i. — SECTION OF NITRO-GLYCERINE CONDUIT : a, lid ; />, lead lining ; c, cinders.
level piece of ground might probably be quite suitable for the purpose of erecting a factory for the manufacture of gun-cotton or gunpowder, and such materials, but would be more or less unsuitable for the manufacture of nitro-glycerine, where a number of buildings are required to be upon different levels, in order to allow of the flow of the liquid nitro-glycerine from one building to
* Explosives Act, 38 Viet. ch. 17.
8 NITRO-EX PLOSIVES.
another through a system of conduits. These conduits (Fig. i), which are generally made of wood and lined with lead, the space between the woodwork and the lead lining, which is generally some 4 or 5 inches, being filled with cinders, connect the various buildings, and should slope gently from one to the other. It is also desirable that, as far as possible, they should be protected by earthwork banks, in the same way as the danger buildings them- selves. They should also be provided with covers, which should be whitewashed in hot weather.
A great deal of attention should be given to these conduits, and they should be very frequently inspected. Whenever it is found that a portion of the lead lining requires repairing, before cutting away the lead it should be very carefully washed, for several feet on either side of the portion that it is intended to remove, with a solution of caustic soda or potash dissolved in methylated spirit and water, and afterwards with water alone. This decomposes the nitro-glycerine forming glycerine and it potassium nitrate. It will be found that the mixed acids attack the lead rather quickly, forming sulphate and nitrate of lead, but chiefly the former. It is on this account that it has been proposed to use pipes made of guttapercha, but the great drawback to their use is that in the case of anything occurring inside the pipes, such as the freezing of the nitro-glycerine in winter, it is more difficult to find it out, and the condition of the inside cannot be seen, whereas in the case of wooden conduits it is an easy matter to lift the lids along the whole length of the conduit.
The buildings which require to be connected by con- duits are of course those concerned with the manu- facture of nitro-glycerine. These buildings are — (i) The nitrating house ; (2) the separating house ; (3) the filter
- •
I v
PROTECTION OF DANGER l!U II. DINGS. 9
house ; (4) the secondary separator ; (5) the deposit of washings ; (6) the settling or precipitation house ; and each of these buildings must be on a level lower than the preceding one, in order that the nitro-glycerine or acids may flow easily from one building to the next. These buildings are, as far as possible, best placed together, and away from the other danger buildings, such as the cartridge huts and dynamite mixing houses, but this is not essential.
All danger buildings should be protected by a light- ning conductor, or covered with barbed wire, as suggested by Professor Oliver J. Lodge, F.R.S., Professors Zenger, of Prague, and Melsens, of Brussels, and everything possible should be done to keep them as cool as possible in the summer. With this object, they should be made double, and the intervening space filled with cinders. The roof also should be kept whitewashed, and the windows painted over thinly with white paint. A thermometer should be suspended in every house. It is very essential that the floors of all these buildings should be washed every day before the work-people leave. In case any nitroglycerine is spilt upon the floors, after sponging it up as far as possible, the floor should be washed with an alcoholic solution of soda or potash to decompose the nitro-glycerine, which it does according to the equation—
CSH5(NO8)3 + 3 KOH = C3H8O3 + jKNO3.
Every one employed in the buildings should wear list or sewn leather shoes, which of course must be worn in the buildings only. The various houses should be connected by paths laid with cinders, or boarded with planks, and any loose sand about the site of the works should be covered over with turf or cinders, to prevent
fO NITRO-EX PLOSIVES.
its blowing about and getting into the buildings. It is a4so' of importance that stand pipes should be placed about the works with a good pressure of water, the n'ecessary hose being kept in certain known places where they can be at once got at in the case of fire., su'ch as the da!nger area laboratory, the foreman's office, &c. It is also desirable that the above precautions- against fire should be tested once a week. With regard to the heating of the various buildings in the winter, steam pipes only should be used, and should be brought from a boiler- house outside the danger area, and should be covered with kieselguhr or fossil meal and tarred canvas. These pipes may be supported upon poles. A stove of some kind should be placed in the corner of each building, but it must be entirely covered in with woodwork, and as small a length of steam pipes should be within the building as possible.
In the case of a factory where nitro-glycerine and dynamite are manufactured, it is necessary that the work-people should wear different clothes upon the danger area than usual, as they are apt to become im- pregnated with nitro-glycerine, and thus not very desir- able or safe to wear outside the works. It is better also that these clothes should not contain any pockets, as this lessens the chance of matches or steel implements being taken upon the danger area. Changing houses, one for the men, and another for the girls, should also be provided. The tools used upon the danger area should, whenever the building is in use, or contains explosives, be made of phosphor bronze or brass, and brass nails or wooden pegs should be used in the construction of all the buildings.
Lightning Conductors. — The Explosive Substances
LIGHTNING CONDUCTORS.
Act, 3'8' Viet. ch. 17, clause 10, says, " Every factory magazine and expense magazine in a factory, and every danger building in a magazine, shall have attached' thereto a sufficient lightning conductor, unless by reas'on of the construction by excavation or the position of su'ch magazine or building, or otherwise, the Secretary of State considers a conductor unnecessary, and every danger building in a factory shall, if so required by the Secretary of State, have attached thereto a sufficient lightning conductor."
The exact form of lightning conductor most suitable for explosive works and buildings has not yet been de- finitely settled. Lightning-rod engineers favour what is known as the Melsens system, due to Professor Melsens, of Brussels, and Professor Zenger, of Prague, but first suggested by the late Professor Clerk- Maxwell. In a paper read before the British Associa- tion, Clerk -Maxwell pro- posed to protect powder- magazines from the effects of lightning by completely surrounding or encasing them with sheqt metal, or a cage of metallic conductors. There were, however, several objections to his system as he left it.
Professor Melsens* has, while using the idea, made several important alterations. He has multiplied the terminals, the conductors, and the earth-connections. His terminals are very numerous, and assume the
FIG. 2.— MELSENS SYSTEM OF LIGHTNING CONDUCTORS.
Belgian Academy of Science.
12 NITRO-EXPLOSIVES.
form of an aigrette or brush with five or seven points, the central point being a little higher than the rest, which form with it an angle of 45°. He employs for the most part galvanised-iron wire. He places all metallic bodies, if they are of any considerable size, in com- munication with the conducting system in such a manner as to form closed metallic circuits. His system is illustrated in Fig. 2, taken from Arms and Explosives. This system is a near approximation to J. C. Max- well's cage. The system was really designed for the protection of powder-magazines or store buildings placed in very exposed situations. Zenger's system is identical with that of Melsens, and has been extensively tried by the Austrian military authorities, and Colonel Hess has reported upon the absolute safety of the system.
The French system of protecting powder-magazines is shown in Fig. 3, where there are no brush terminals or
aigrettes. The French mili- tary authorities also protect magazines by erecting two or more lightning-rods on poles of sufficient height
F,G. 3.-FKENCH SYSTEM OF placed close to, but not tOUCll-
ing, the walls of the magazine.
These conductors are joined below the foundations and earthed as usual.
In the instructions issued by the Government, it is stated that the lightning-rods placed upon powder-mills should be of such a height, and so situated, that no danger is incurred in igniting the powder-dust in the air by the lightning discharge at the pointed rod. In such a case a fork or aigrette of five or more points should invariably be used in place of a single point.
In Fig. 4 (a and b} is shown the Government method
VARIOUS SYSTEMS OF PROTECTION. 13
for protecting buildings in which explosives are made or stored. Multiple points or aigrettes would be better. Lord Kelvin and Professor Melsens favour points, and it
FIG. 4*.— GOVERNMENT SYSTEM OF LIGHTNING CONDUCTORS FOR LARGE BUILDINGS.
is generally admitted that lightning does not strike build- ings at a single point, but rather in a sheet; hence, in such cases, or in the event of the globular form being assumed
FIG. 4/5.— GOVERNMENT SYSTEM OF LIGHTNING CONDUCTORS FOR SMALL BUILDINGS.
by the lightning, the aigrette will constitute a much more effective protection than a single point. As to the spac- ing of conductors, they may, even on the most important
14 NITRO-EXPLOSIVES.
buildings, be spaced at intervals of 50 feet. There will then be no point on the building more than 25 feet from the conductor. This "25-feet rule" can be adhered to with advantage in all overground buildings for explo- sives.
Underground magazines should, whenever possible, also be protected, because, although less exposed than overground buildings, they frequently contain explosives packed in metal cases, and hence would present a line of smaller electrical resistance than the surrounding earth would offer to the lightning. The conductor should be arranged on the same system as for overground build- ings, but be applied to the surface of the ground over the magazines.
In all situations where several conductors are joined in one system, the vertical conductors should be con- nected both at the top and near the ground line. The angles and the prominent portions of a building being the most liable to be struck, the conductors should be carried over and along these projections, and therefore along the ridges of the roof. The conductors should be connected to any outside metal on the roofs and walls, and specially to the foot of rain-water pipes.
All the lightning conductors should be periodically tested, to see that they are in working condition, at least every three months, according to Mr Richard Anderson. The object of the test is to determine the resistance of the earth-connection, and to localise any defective joints or parts in the conductors. The best system of testing the conductors is to balance the resistance of each of the earths against the remainder of the system, from which the state of the earths may be inferred with sufficient accuracy for all practical purposes.
Captain Bucknill, R.E., has designed an instrument
NITRO-GLYCERINE. 1 5
to test resistance which is based on the Post Office pattern resistance coil, and is capable of testing to approximate accuracy up to 200 ohms, and to measure roughly up to 2,000 ohms. Mr R. Anderson's apparatus is also very handy, consisting of a case containing three Leclanch£ cells, and a galvanometer with a " tangent " scale and certain standard resistances. Some useful articles on the protection of buildings from lightning will be found in Anns and Explosives, July, August, and September 1892, and by Mr Anderson, Brit. Assoc., 1878-80.
Nitro-Glycerine. — One of the most powerful of modern explosive agents is nitro-glycerine. It is the explosive contained in dynamite, and forms the greater part of the various forms of blasting gelatines, such as gelatine dynamite and gelignite, both of which substances consist of a mixture of gun-cotton dissolved in nitro- glycerine, with the addition of varying proportions of wood-pulp and saltpetre, the latter substances acting as absorbing materials for the viscid gelatine. Nitro- glycerine is also largely used in the manufacture of smokeless powders, such as cordite, ballistite, and several others.
Nitro-glycerol, or glycerol tri-nitrate, was discovered by Sobrcro in the year 1847. In a letter written to M. Pelouse, he says, " when glycerol is. poured into a mixture of sulphuric acid of a specific gravity of 1.84, and of nitric acid of a gravity of 1.5, which has been cooled by a freezing mixture, that an oily liquid is formed." This liquid is nitro-glycerol, or nitro-glycerine, which for some years found no important use in the arts, until the year 1863, when Alfred Nobel first started a
factory in Stockholm for its mnnufaoture upon a large
f * OF THE (tTNIVERS:
t
J
1 6 NITRO-EXPLOSIVES.
scale ; but on account of some serious accidents taking place, its use did not become general.
It was not until Nobel conceived the idea (in 1866) of absorbing the liquid in some absorbent earth, and thus forming the material that is now known as dyna- mite, that the use of nitro -glycerine as an explosive became general.
Among those who improved the manufacture of nitre-glycerine was Mowbray, who, by using pure gly- cerine and nitric acid free from nitrous acid, made very great advances in the manufacture. Mowbray was pro- bably the first to use compressed air for the purpose of keeping the liquids well agitated during the process of nitration, which he conducted in earthenware pots, each containing a charge of 17 Ibs. of the mixed acids and 2 Ibs. of glycerol.
A few years later (1872), MM. Vouges and Boutnny* proposed to prepare nitro-glycerine by mix- ing the sulphuric acid with the glycerine, thus forming a sulpho-glyceric acid, which was afterwards mixed with a mixture of nitric and sulphuric acids. They claimed for this method of procedure that the final temperature is much lower. The two mixtures are mixed in the pro- portions— Glycerine, 100; nitric acid, 280; and sulphuric acid, 600. They state that the rise of temperature upon mixing is limited from 10° to 15° C. ; but this method requires a period of twenty-four hours to complete the nitration, which, considering the danger of keeping the nitro-glycerine in contact with the mixed acids for so long, probably more than compensates for the somewhat doubtful advantage of being able to perform the nitra- tion at such a low temperature. The Boutnny process
* Comples Rendits, 75; and Desortiaux, Trait e sur la Poudrc, 684-686,
CHEMICAL STRUCTURE OF NITRO-GLYCERINE. I/
was in operation for some time at Pembrey Burrows in Wales, but after a serious explosion the process was abandoned.
Nitro-glycerine is now generally made by adding the glycerine to a mixture of sulphuric and nitric acids. The sulphuric acid, however, takes no part in the re- \ action, but is absolutely necessary to combine with the water that is formed by the decomposition, and thus to keep up the strength of the nitric acid, otherwise lower nitrates of glycerine would be formed that are soluble in water, and which would be lost in the subsequent process of washing to which the nitro compound is subjected, in order to remove the excess of acids, the retention of which in the nitro-glycerol is very dangerous. Nitro- glycerol, which was formerly considered to be a nitro- substitution compound of glycerol, was thought to be formed thus —
but more recent researches rather point to its being re- garded as a nitric ether of glycerol, or glycerine, and to its being formed thus —
92 227
(OH
The formula of glycerine is C3H8O3, or C3H5< OH
(OH
fONO2 and that of the mono-nitrate of glycerine Q»Hs-< OH
(OH
(
and of the tri-nitrate (or nitro-glycerine) C3H5-< ONO2
(ONO2
that is, the three hydrogens of the semi-molecules of
B
1 8 NITRO-EX PLOSIVES.
hydroxyl in the glycerine have been replaced by the NO2. group.
In the manufacture upon the large scale, a mixture of three parts by weight of nitric acid and five parts of sulphuric acid are used. From the above equation it will be seen that every I Ib. of glycerol should give
2.47lbs.ofnitro1glycerol V = 2.47, but in practice
the yield is only about 2 Ibs. to 2j, the loss being accounted for by the unavoidable formation of some of the lower nitrate, which dissolves in water, and is thus washed away, and partly perhaps to the presence of a little water (or other non-nitratable matter) in the glycerine, but chiefly to the former, which is due to the acids having become too weak.
CHAPTER II. MANUFACTURE OF NITROGLYCERINE.
Properties of Nitro- Glycerine. — Nitro-glycerol is a heavy oily liquid of specific gravity 1.6 at 15° C., and when quite pure is colourless. The commercial product is a pale straw yellow, but varies much according to the purity of the materials used in its manufacture. It is insoluble in water, crystallises at - 20° C., but different commercial samples behave very differently in this re- spect, and minute impurities prevent or delay crystallisa- tion. Solid nitro-glycerol melts at 10° C., but requires to be exposed to this temperature for some time before melting. The specific gravity of the solid form is 1.735 at + 10° C. ; it contracts one-twelfth of its volume in solidifying. Beckerheim * gives the specific heat as 04248 between the temperatures of 9.5° and 9.8° C.
Nitro-glycerine has a sweet taste, and causes great depression and vertigo. It is soluble in ether, chloro- form, benzene, glacial acetic acid, and nitro-benzerie, in 1.75 parts of methylated spirit, very nearly insoluble in water, and practically insoluble in carbon bisulphide. Its formula is C3H5(NO3)3, and molecular weight 227. When pure, it may be kept any length of time without decomposition. Berthelot kept a sample for ten years, and Mr G. M' Roberts, of the Ardeer Factory, for nine years, without their showing signs of decomposition ;
* Isb., Chem. Tech., 22, 481-487. 1876.
20 NITRO-EXPLOSIVES.
i but if it should contain the smallest trace of free acid, <' decomposition is certain to be started before long. This will generally show itself by the formation of little green spots in the gelatine compounds, or a green ring upon the surface of liquid nitro-glycerine. Sunlight will often cause it to explode ; in fact, a bucket containing some water that had been used to wash nitro-glycerine, and had been left standing in the sun, has in our experience been known to explode with considerable force. The percentage composition of nitro-glycerine is as fol- lows : —
Found. Theory for C3H6(NOS),.
Carbon 15.62 15.86 per cent.
Hydrogen - 2.40 2.20 ,,
Nitrogen 17.90 18.50 „
Oxygen 63.44 „
The above analysis is by Beckerheim. Sauer and Adou give the nitrogen as 18.35 to 10.54 Per cent, by Dumas' method ; but I have never found any difficulty in obtain- ing percentages as high as 18.46 by the use of Lunge's nitrometer. The decomposition products by explosion are shown by the following equation—
2C8H5(NO8)8 = 6CO2+5H2O + 6N + O ; that is, it contains an excess of 3.52 per cent, of oxygen above that required for complete combustion ; 100 grins! would be converted into —
Carbonic acid (CO)., 58.15 per cent.
Water - - 19.83
Oxygen - . . - 3.52 „
Nitrogen - 18.50 „
The volume of gases produced at o° and 760 mm., calculated from the above, is 714 litres per kilo, the water being taken as gaseous. Nitro-glycerine is decomposed differently if it is ignited as dynamite (i.e., kieselguhr
PROPERTIES OF NITRO-GLYCERINE. 21
dynamite), and if the gases are allowed to escape freely
under a pressure nearly equal to that of the atmosphere.
Sarrau and Vieille obtained under these conditions, for
100 volumes of gas—
NO 48.2 per cent.
CO 35.9
CO, 12.7
H - 1.6 „
N 1.3 „
CH4 0.3 „
These conditions arc similar to those under which a mining charge, simply ignited by the cap, burns away slowly under a low pressure (/>., a miss fire). In a recent communication, P. F. Charon (Engineering and Mining Journal, 1892) says, that in practice nitro- glycerine vapour, carbon monoxide, and nitrous oxide, are also produced as the result of detonation, but he attributes their formation to the use of a too feeble detonator.
Nitro-glycerine explodes very violently by concus- sion. It may be burned in an open vessel, but if heated above 250° C. it explodes. Professor C. E. Munroc gives the firing point as 2O3°-2O5° C. He used the apparatus devised by Horsley. The heat of formation of nitro-glycerme, as deduced from the heat of combus- tion by M. Longuinine, is 432 calories for I grm. ; and the heat of combustion equals 1,576 cals. for I grm. In the case of nitro-glycerine, the heat of total .combustion and the heat of complete decomposition are interchangeable terms, since it contains an excess of oxygen. Accord- ing to Dr W. H. Perkin, F.R.S.,* the magnetic rotation of nitro-glycerine is 5.407, and that of tri-methylcnc nitrate, 4.769 (cliff. =.638). Dr Perkin says: "Had nitro- glycerine contained its nitrogen in any other combination
* Jour. Chew. Soc., W. H. Perkin, 1889, p. 726.
22 NITRO-EXPLOSIVES.
with oxygen than as — O-NO2, as it might if its con- stitution had been represented as C3H2(NO2)3(OH)3, the rotation when compared with propyl nitrate (4.085) would be abnormal."
Manufacture of Nitro-Glycerine. — Nitro-glycerine is prepared upon the manufacturing scale by gradually adding glycerine to a mixture of nitric and sulphuric acids of great strength. The mixed acids are contained in a lead vessel, which is kept cool by a stream of water continually passing through worms in the interior of the nitrating vessel, and the glycerine is gradually added in the form of a fine stream from above. The manufac- ture can be divided into three distinct operations, viz., nitration, separation, and washing, and it will be well to describe these operations in the above order.
Nitration. — The most essential condition of nitrating is the correct composition and strength of the mixed acids. The best proportions have been found to be three parts by weight of nitric acid of a specific gravity 1.525 to 1.530, and containing as small a proportion of the oxides of nitrogen as possible, to five parts by weight of sulphuric acid of a specific gravity of 1.840 at 15° C, and about 97 per cent, of mono-hydrate. It is of the very greatest importance that the nitric acid should be as strong as possible. Nothing under a gravity of 1.52 should ever be used even to mix with stronger acid, and the nitration will be proportional to the strength of the acid used, provided tHe sulphuric acid is also strong enough. It is also of great importance that the oxides of nitrogen should be low, and they should be kept ^down to as low as I per cent., or even lower. It is also very desirable that the nitric acid should contain as little
NITRATION OF GLYCERINE. 23
chlorine possible. The following is the analysis of a sample of nitric acid, which gave very good results upon the commercial scale : — Specific gravity, 1.525, N2O4, 1.03 per cent. ; nitric acid (HNO3), 95.58 per cent.
The amount of real nitric acid (mono-hydrate) andi the amount of nitric peroxide present in any sample! should always be determined before it is used for nitraty ing purposes. The specific gravity is not a sufficient guide to the strength of the acid, as an acid having a. high gravity, due to some 3 or 4 per cent, of nitric oxidesX in solution, will give very poor nitration results. A tenth I normal solution of sodium hydroxide (NaOH), with phenol-phthalein as indicator, will be found the most convenient method of determining the total acid present. The following method will be found to be very rapid and reliable: — Weigh a 100 c.c. flask, containing a few cubic centimetres of distilled water, and then add from a pipette I c.c. of the nitric acid to be examined, and reweigh (this gives the weight of acid taken). Now make up to 100 c.c. at 15° C. ; shake well, and take out 10 c.c. with a pipette ; drain into a small Erlenmeyer flask, and add a little of the phenol-phthalein solution, and titrate with the tenth normal soda solution.
The nitric peroxide can be determined with a solu- tion of potassium permanganate of - strength, thus :
Take a small conical flask, containing -about 10 c.c. of water, and add from a burette 10 to 16 c.c. of the per- manganate solution ; then add 2 c.c. of the acid to be tested, and shake gently, and continue to add perman- ganate solution as long as it is decolorised, and until a faint pink colour is permanent.
Example.— permanganate 3.16 grm. per litre, I
24 NITRO-EXPLOSIVES.
c.c. = 0.0046 grm. N2O4, 2 c.c. of sample of acid specific gravity 1.52 = 3.04 grm. taken for analysis. Took 20 c.c. permanganate solution, 0.0046 x 20 = .092 grm. N2O4, and
.092 x ioo = ^Q2 per cent N2O4. The specific gravity
3-°4
should be taken with an hydrometer that gives the specific gravity directly, or, if preferred, the 2 c.c. of acid may be weighed.
A very good method of rapidly determining the strength of the sulphuric acid is as follows : — Weigh out in a small weighing bottle, as nearly as possible, 2.45 grms. This is best done by running in 1.33 c.c. of the acid (1.33 X 1.84 = 2.44^). Wash into a large Erlenmeyer flask, carefully washing out the bottle, and also the stopper, &c. Add a drop of phenol-phthalein solution and titrate, with a half normal solution of sodium hydrate (use a 100 c.c. burette). Then if 2.45 grm. exactly have been taken, the readings on the burette will equal per- centages of H2SO4 (mono-hydrate) ; if not, calculate thus: — 2.444 grm. weighed, required 95.4 c.c. NaOH. Then-
2.444 : 95.4 : : 2.45 : ^=95.64 per cent. H2SO4.
It has been proposed to free nitric acid from the oxides of nitrogen by blowing compressed air through it, and thus driving the gases in solution out. The acid was contained in a closed lead tank, from which the escaping fumes were conducted into the chimney shaft, and on the bottom of which was a lead pipe, bent in the form of a circle, and pierced with holes, through which the compressed air was made to pass ; but the process was not found to be of a very satisfactory nature, and it is certainly better not to allow the formation 'of these compounds in the manufacture of the acid in the first
MIXING THE ACIDS FOR NITRATION. 25
instance. Another plan, however, is to heat the acid gently, and thus drive out the nitrous gases. Both processes involve loss of nitric acid.
Having obtained nitric and sulphuric acids as pure as possible, the next operation is to mix them. This is best done by weighing the carboys in which the acids are generally stored before the acids are drawn off into them from the condense'rs, and keeping their weights constantly attached to them by means of a label. It is then a simple matter to weigh off as many carboys of acid as may be required for any number of mixings, and subtract the weights of the carboys. The two acids should, after being weighed, be poured into a tank and mixed, and subsequently allowed to flow into an acid egg or montjus, to be afterwards forced up to the nitrat- ing house in the danger area. The montjus or acid egg is a strong cast-iron tank, of either an egg shape, or a cylinder with a round end. If of the former shape, it would lie on its side, and upon the surface of the ground, and would have a manhole at one end, upon which a lid would be strongly bolted down ; but if of the latter shape, the lid, of course, is upon the top, and the montjus itself is let into the ground. In either case, the principle is the same. One pipe, made of stout lead, goes to the bottom, and another just inside to convey the compressed air, the acids flowing away as the pressure is put on, just as blowing down one tube of an ordinary wash-bottle forces the water up the other tube to the jet. The pressure ^necessary will, of course, vary immensely, and will depend upon the height to which the acid has to be raised and the distance to be traversed.
The mix,ed acids having been forced up to the danger area, and to a level higher than the position of the nitrating house, should, before being used, be allowed to
26 NITRO-EXPLOSIVES.
cool, and leaden tanks of sufficient capacity to hold at least enough acid for four or five nitrations should be placed in a wooden house upon a level at least 6 or 7 feet above the nitrating house. In this house also should be a smaller lead tank, holding, when filled to a certain mark, just enough of the mixed acids for one nitration. The object of this tank is, that as soon as the man in charge knows that the 'last nitration is finished, he refills this smaller tank (which contains just enough of the mixed acids), and allows its contents to flow down into the nitrating house and into the nitrator, ready for the next nitration. The nitration is usually conducted in a vessel constructed of lead, some 4 feet wide at the bottom, and rather less at the top, and about 4 feet or so high. The size, of course, depends upon the volume of the charge it is intended to nitrate at one operation, but it is always better that the tank should be only two- thirds full. A good charge is 16 cwt. of the mixed acids, in the proportion of three to five ; that is, 6 cwt. of nitric acid, and 10 cwt. of sulphuric acid, and 247 Ibs. of glycerine.
Upon reference to the equation showing the forma- tion of nitro-glycerine, it will be seen that for every I Ib. of glycerine 2.47 Ibs. of nitro-glycerine should be furnished,* but in practice the yield is only about 2 \ Ibs., the loss being accounted for by the unavoidable forma- tion of some of the lower nitrate of glycerine (the mono- nitrate), which afterward dissolves in the washing waters. The lead tank (Fig. 5) is generally cased in woodwork,with a platform in front for the man in charge of the nitrating to stand upon, and whence to work the various taps.
* Thus if 92 Ibs. glycerine give 227 Ibs. nitro-glycerine,
?272U=2.47lbS. 92
CONSTRUCTION OF THE NITRATOR. 2?
The top of the tank is closed in with a dome of lead, in which is a small glass window, through which the pro- gress of the nitrating operation can be watched. From the top of this dome is a tube of lead which is carried up through the roof of the building. It serves as a chimney to carry off the acid fumes which are given off during the nitration. The interior of this tank contains at least
FIG. 5. — TOP OF NITRATOR. A, Fume Pipe; B, Water Pipes for Cooling ; C, Acid Mixture Pipe ; E, Compressed Air ; G, Glycerine Pipe and Funnel ; T, Thermometer ; IV, Window.
three concentric spirals of at least i-inch lead pipe, through which water can be made to flow during the iv/iole operation of nitrating. Another lead pipe is carried through the dome of the tank, as far as the bottom, where it is bent round in the form of a circle. Through this pipe, which is pierced with small holes, about I inch apart, compressed air is forced at a pressure of
28 NITRO-EXPLOSIVES.
about 60 Ibs. in order to keep the liquids in a state of constant agitation during the whole period of nitration. There must also be a rather wide pipe, of say 2 inches internal diameter, carried through the dome of the tank, which will serve to carry the mixed acid to be used in the operation, into the tank. There is still another pipe to go through the dome, viz., one to carry the glycerine into the tank. This need not be a large bore pipe, as the glycerine is generally added to the mixed acids in a thin stream (an injector is often used).
Before the apparatus is ready for use, it requires to have two thermometers fixed, one long one to reach to the bottom of the tank, and one short one just long enough to dip under the surface of the acids. When the tank contains its charge, the former gives the tempera- ture of the bottom, and the latter of the top of the mixture. The glycerine should be contained in a small cistern, fixed in some convenient spot upon the wall of the nitrating house, and should have a pipe let in flush with the bottom, and going through the dome of the nitrating apparatus. It must of course be provided with a tap or stop-cock, which should be placed just above the point where the pipe goes through the lead dome.
Sorne method of measuring the quantity of glycerine used must be adopted. A gauge-tube graduated in inches is a very good plan, but it is essential that the graduations should be clearly visible to the operator upon the platform in front of the apparatus. A large tap made of earthenware (and covered with lead) is fixed in the side of the nitrating tank just above the bottom, to run off the charge after nitration. This should be so arranged that the charge may be at option run down the conduit to the next house or discharged into a drowning tank, which may sometimes be necessary in
POINTS TO BE ATTENDED TO IN THE NITRATION. 29
cases of decomposition. The drowning tank is generally some 3 or 4 yards long and several feet deep, lined with cement, and placed close outside the building.
The apparatus having received a charge of mixed acids, the water is started running through the pipes coiled inside the tank, and a slight pressure of com- pressed air is turned on, to mix the acids up well before starting. The nitration should not be commenced until the two thermometers register a temperature of 18° C. The glycerine tap is then partially opened, and the glycerine slowly admitted, and the compressed air turned on full, until the contents of the apparatus are in a state of very brisk agitation. A pressure of about 40" Ibs. is about the minimum (if 247 Ibs. of glycerine and 16 cwt. of acids are in the tank.) If the glycerine tube is fitted with an injector, it may be turned on almost at once. The nitration will take about thirty minutes to complete, but the compressed air and water should be kept on for an additional ten minutes after this, to give time for all the glycerine to nitrate. The temperature should be kept as low as possible.
The chief points to attend to during the progress of the nitration are : —
1. The temperature registered by the two, ther- mometers.
2. The colour of the nitrous fumes given off (as seen through the little window in the dome of the apparatus).
3. The pressure of the compressed air as seen from a gauge fixed upon the air pipe just before it enters the apparatus.
4. The gauge showing the quantity of glycerine used.
The temperature, as shown by either of the two ther- mometers, should not be at any time higher than 25° C. If it rises much above this point, the glycerine should be
30 NITRO-EXPLOSIVES.
at once shut off, and the pressure of air increased for some few minutes until the temperature falls, and no more red fumes are given off.
The nitration being finished, the large earthenware tap at the bottom of the tank is opened, and the charge allowed to flow away down the conduit to the next building, i.e.t to the separator.
The nitrating house is best built of wood, and should have a close-boarded floor, which should be kept scrupu- lously clean, and free from grit and sand. A wooden pail and a sponge should be kept in the house in order that the workman may at once clean up any mess that may be made, and a small broom should be handy, in order that any sand, &c., may be at once removed. It is a good plan for the nitrator to keep a book in which he records the time of starting each nitration, the temperature at starting and at the finish, the time occupied, and the date and number of the charge, as this enables the foreman of the danger area at any time to see how many charges have been nitrated, and gives him other useful information conducive to safe working. Quite lately Edward Liebert has devised an improve- ment in the treatment of nitro-glycerine. He adds ammonium sulphate or ammonium nitrate to the mixed acids during the operation of nitrating, which he claims destroys the nitrous acid formed according to the equation —
I am not aware that this modification of the process of nitration is in use at the present time.
.The newly made charge of nitro-glycerine, upon leaving the nitrating house, flows away down the con- duit, either made of rubber pipes, or better still, of
DIVERS
POSITION OF THE
woodwork, lined with lead and covered with lids made of wood (in short lengths), in order that by lifting them at any point the condition of the conduit can be ex- amined, as this is of the greatest importance, and the conduit requires to be frequently washed out and the sulphate of lead removed. This sulphate always con- tains nitro-glycerine, and should therefore be burnt in some spot far removed from any danger building or magazine, as it frequently explodes with considerable violence.
In works where the manufacture of nitro-glycerine is of secondary importance, and some explosive contain- ing only perhaps 10 per cent, of nitro-glycerine is manufactured, and where 50 or 100 Ibs. of glycerine are nitrated at one time, a very much smaller nitrating apparatus than the one that has been already described will be probably all that is required. In this case the form of apparatus shown in Fig. 6 will be found very satisfactory. It should be made of stout lead (all lead used for tanks, &c., must be " chemical lead "), and may be made to hold 50 or 100 Ibs., as found most convenient. This ni- trator can very well be placed in the same house as the separator ; in fact, where such a small quantity of nitro-
* J
glycerine is required, the whole series of operations, nitrating, separation, and washing, &c., may very well be performed in the same building. It will of course be necessary to place the nitrator on a higher level than the separator, but this can easily be
FIG. 6.— SMALL NITRA- TOR. N, Tap for Discharg- ing ; P, Water Pipes ; T, Thermometer ; W ', Win- dows; P1, Glycerine Pipe.
32 NITRO-EXPLOSIVES.
done by having platforms of different heights, the nitra- tion being performed upon the highest. The construction of this nitrator is essentially the same as in the larger one, the shape only being somewhat different. Two water coils will probably be enough, and one thermo- meter. It will not be necessary to cover this form in with woodwork.
Separation. — The nitro-glycerine, together with the mixed acids, flows from the nitrating house to the separating house, which must be on a lower level than the former. The separating house contains a large lead- lined tank, closed in at the top with a wooden lid, into
FIG. 7. — SEPARATOR. A, Compressed Air Pipes; G, Nitro-glycerine enters from Nitrator ; N, Nitro-glycerine to P ; L, Lantern Window ; \V, Win- dow in Side ; S, Waste Acids to Secondary Separator ; 'f, Tap to remove last traces of Nitro-glycerine. /J, Lead Washing Tank ; A, Compressed Air ; Wt Water-pipe ; N, Nitro-glycerine from Separator.
which a lead pipe of large bore is fixed, and which is carried up through the roof of the building, and acts as a chimney to carry off any fumes. A little glass window should be fixed in this pipe in order that the colour of the escaping fumes may be seen. The conduit con-
SEPARATION OF THE NITRO-GLYCERINE. 33
veying the nitro-glycerine enters the building close under the roof, and discharges its contents into the tank through the pipe G (Fig. 7). The tank is only about two-thirds filled by the charge. There is in the side of the tank a small window of thick plate glass, which enables the workman to see the level of the charge, and also to observe the progress of the separation, which will take from thirty minutes to one hour.
The tank should be in connection with a drowning tank, as the charge sometimes gets very dangerous in this building. It must also be connected by a conduit with the filter house, and also to the secondary separator by another conduit. The tank should also be fitted with a compressed air pipe, bent in the form of a loop. It should lie upon the bottom of the vat. The object of this is to mix up the charge in case it should get too hot through decomposition. A thermometer should of course be fixed in the lid of the tank, and its bulb should reach down to the middle of the nitro-glycerine (which rests upon the surface of the mixed acids, the specific gravity of the nitro-glycerine being 1.6, and that of the waste acids 1.7, the composition of the acids is now 11 per cent. HNO3, 67 per cent. H2SO4, and 22 per cent, water), and the temperature carefully watched.
If nothing unusual occurs, and it has not been neces- sary to bring the compressed air into use, and so disturb the process of separation, the waste acids may be run away from beneath the nitro-glycerine, and allowed to flow away to the secondary separator, where any further quantity of nitro-glycerine that they contain separates out after resting for some days. The nitro-glycerine itself is run into a smaller tank in the same house, where it is washed three or four times with its own bulk of water, containing about 3 Ibs. of carbonate of soda
C
34
N ITRO-.EXPLOSI VES.
W
to neutralise the remaining acid. This smaller tank should contain a lead pipe, pierced and coiled upon the bottom, through which compressed air may be passed, in order to stir up the charge with the water and soda. After this preliminary washing, the nitro-glycerine is drawn off into indiarubber buckets, and poured down the conduit to the filter house. The wash waters may
be sent down a conduit to another building, in order to allow the small quantity of nitro-glycerine that has been retained in the water as minute globules to settle, if thought worth the trouble of saving. This, of course, will depend upon the usual out-turn of nitro-glycerine in a day, and the general scale of operations.
Filtering and Washing.
—The filter house (Fig. 8), which must of course be again on a somewhat lower level than the separating house, must be a considerably larger building than either the ni- trating or separating houses, as it is always necessary to be washing some five or six c^es at the same time.
Upon the arrival of the nitr°-
glycerine at this hoUSC, it
first flows into a lead-lined wooden tank (w), containing a compressed air pipe, just like the one in the small
B2, Indiarubber Bucket.
FILTERING AND WASHING. 35
tank in the separating house. This tank is half filled with water, and the compressed air is turned on from half to a quarter of an hour after the introduction of the charge. The water is then drawn off, and fresh water added. Four or five washings are generally necessary. The nitro-glycerine is then run into the next tank (A), the top of which is on a level with the bottom of the first one. Across the top of this tank is stretched a frame of flannel, through which the nitro-glycerine has to filter. This removes any solid matters, such as dirt or scum. Upon leaving this tank, it passes through a similar flannel frame across another tank (B), and is finally drawn off by a tap in the bottom of the tank into rubber buckets. The taps in these tanks are best made of vulcanite.
At this stage, a sample should be taken to the laboratory and tested. If the sample will not pass the tests, which is often the case, the charge must be re- washed for one hour, or some other time, according to the judgment of the chemist in charge. In the case of an obstinate charge, it is of much more avail to wash a large number of times with small quantities of water, and for a short time, than to use a lot of water and wash for half an hour. Plenty of compressed air should be used, as the compound nitric ethers which are formed are thus got rid of. As five or six charges are often in this house at one time, it is necessary to have as many tanks arranged in tiers, otherwise one or* two refractory charges would stop the nitrating house and the rest of the nitro-glycerine plant. The chief causes of the washed material not passing the heat test are, either that the acids were not clean, or they contained objectionable impurities, or more frequently, the quality of the glycerine used. The glycerine used for making nitro-glycerine .should conform to the following tests, some of which,
36 NITRO-EXPLOSIVES.
however, are of greater importance than others. The glycerine should —
1. Have minimum specific gravity at 15° C. of 1.261.
2. Should nitrify well.
3. Separation should be sharp within half an hour, without the separation of flocculent matter, nor should any white flocculent matter (due to fatty acids) be formed when the nitrated glycerine is thrown into water and neutralised with carbonate of soda.
4. Should be free from lime and chlorine, and con- tain only traces of arsenic, sulphuric acid, &c.
5. Should not leave more than 0.25 per cent, of inorganic and organic residue together when evaporated in a platinum dish without ebullition (about 160° C.) or partial decomposition.
6. Silver test fair.
7. The glycerine, when diluted one-half, should give no deposit or separation of fatty acids when nitric per- oxide gas is passed through it. (Nos. I, 2, 3 and 5 are the most essential.)
The white flocculent matter sometimes formed is a very great nuisance, and any sample of glycerol which gives such a precipitate when tried in the laboratory should at once be rejected, as it will give no end of trouble in the separating house, and also in the filter house, and it will be very difficult indeed to make the nitro-glycerine pass the heat test. The out-turn of nitro-glycerine also will be very low. The trouble will show itself chiefly in the separating operation. Very often 2 or 3 inches will rise to the surface or hang about in the nitro-glycerine, and at the point of contact between it and the mixed acids, and will afterwards be very difficult to get rid of by filtration. The material appears to be partly an emulsion of the glycerine, and partly
TESTING THE NITROGLYCERINE. 37
due to fatty acids, and as there appears to be no really satisfactory method of preventing its formation, or of getting rid of it, the better plan is not to use any glycerine for nitrating that has been found by experiment upon the laboratory scale to give this objectionable matter. One of the most useful methods of testing the glycerine, other than nitrating, is to dilute the sample one-half with water, and then to pass a current of nitric peroxide gas through it, when a flocculent precipitate of elai'dic acid (less soluble in glycerine than the original oleic acid) will be formed. Nitrogen peroxide, N2O4, is best obtained by heating dry lead nitrate (see Allen, "Commercial Organic Analysis," vol. ii., 301).
When a sample of nitro-glycerine is brought to the laboratory from the filter house, it should first be examined to see that it is not acid. A weak solution of Congo red or methyl orange may be used. If it appears to be decidedly alkaline, it should be poured into a separating funnel, and shaken with a little distilled water. This should be repeated, and the washings (about 400 c.c.) run into a beaker, a drop of Congo red or methyl orange
added, and a drop or so of — hydrochloric acid added,
when it should give, with two or three drops at most, a blue colour with the Congo red, or pink with the methyl orange, &c. The object of this test is to show that the nitro-glycerine is free from any excess of soda, i.e.y that the soda has been properly washed out, otherwise the heat test will show the sample to be better than it is. The heat test must also be applied.
Upon leaving the filter house, where it has been washed and filtered, and has satisfactorily passed the heat test, it is drawn off from the lowest tank in india- rubber buckets, and poured down the conduit leading to
38 NITRO-EXPLOSIVES.
the precipitating house, where it is allowed to stand for a day, or sometimes longer, in order to allow the little water it still contains to rise to the surface. In order to accomplish this, it is sufficient to allow it to stand in covered-in tanks of a conical form, and about 3 or 4 feet high. In many works it is previously filtered through common salt, which of course absorbs the last traces of water. It is then of a pale yellow colour, and should be quite clear, and can be drawn off by means of a tap (of vulcanite), fixed at the bottom of the tanks, into rubber buckets, and is ready for use in the preparation of dynamite, or any of the various forms of gelatine com- pounds, smokeless powders, &c., such as cordite, ballistite, and many others.
The Waste Acids. — The waste acids from the separating house, from which the nitro-glycerinc has been as completely separated as possible, are run down the conduit to the secondary separator, in order to recover the last traces of nitro-glycerine that they contain. The composition of the waste acids is generally some- what as follows: — Specific gravity, 1.7075 at 15° C. ; sulphuric acid, 67.2 per cent. ; nitric acid, 1 1.05 percent. ; and water, 21.7 per cent., with perhaps as much as 2 per cent, of nitric oxide, and of course varying quantities of nitro-glycerine, which must be separated, as it is impossible to run this liquid away (unless it can be run into the sea) or to recover the acids by distillation as long as it contains this substance. The mixture, there- fore, is generally run into large circular lead-lined tanks, covered in, and very much like the nitrating apparatus in construction, that is, they contain worms coiled round inside, to allow of water being run through to keep the mixture cool, and a compressed air pipe, in order to
THE WASTE ACIDS. 39
agitate the mixture if necessary. The top also should contain a window, in order to allow of the interior being seen, and should have a leaden chimney to carry off the fumes which may arise from decomposition. It. is also useful to have a glass tube of 3 or 4 inches in diameter substituted for about a foot of the lead chimney, in order that the man on duty can at any time see the colour of the fumes arising from the liquid. There should also be two thermometers, one long one reaching to the bottom of the tank, and one to just a few inches below the surface of the liquid.
The nitro-glycerine, of course, collects upon the surface, and can be drawn off by a tap placed at a convenient height for the purpose. The cover of the tank is generally conical, and is joined to a glass cylinder, which is cemented to the top of this lead cover, and also to the lead chimney. In this glass cylinder is a hole into which fits a ground glass stopper, through which the nitro-glycerine can be drawn off. There will probably never be more than an inch of nitro-glycerine at the most, and seldom that. It should be taken to the filter house and treated along with another charge. The acids themselves may either be run to waste, or better treated by some denitration plant. This house probably requires more attention than any other in the danger area, on account of the danger of the decomposition of the small quantities of nitro-glycerine, which, as it is mixed with such a large quantity of acids and water, is very apt to become hot, and decomposition, which sets up in spots where a little globule of nitro-glycerine is floating, surrounded by acids that gradually get hot, gives off nitrous fumes, and perhaps explodes, and thus causes the sudden explosion of the whole. The only way to prevent this is for the workman in charge to look at the
4O NltRO-EXPLOSlVES.
thermometers frequently, and at the colour of the escaping fumes, and if he should notice a rise of temperature or any appearance of red fumes, to turn on the water and air, and stir up the mixture, when probably the tem- perature will suddenly fall, and the fumes cease to come off.
The cause of explosions in this building is either the non-attention of the workmen in charge, or the bursting of one of the water pipes, by which means, of course, the water, finding its way into the acids, causes a sudden rise of temperature. If the latter of these two causes should occur, the water should at once be shut off and the air turned on full, but if it is seen that an explosion is likely to occur, the tank should at once be emptied by allowing its contents to run away into a drowning tank placed close outside the house, which should be about 4 feet deep, and some 16 feet long by 6 feet wide ; in fact, large enough to hold a considerable quantity of water. But this last course should only be resorted to as a last extremity, as it is extremely troublesome to recover the small quantity of nitro-glycerine from the bottom of this tank, which is generally a bricked and cemented excavation some few yards from the house.
It has been proposed to treat these waste acids, con- taining nitro-glycerine, in Mr M. Prentice's nitric acid retort. In this case they would be run into the retort, together with nitrate of soda, in a fine stream, and the small quantity of nitro-glycerine, coming into contact with the hot mixture already in the retort, would pro- bably be at once decomposed. This process, although not yet tried, promises to be a success. Several processes have been used for the denitration of these acids. One that has been largely used is to run the acids down a tower through which a current of steam is made to pass
GUTTMANN'S AND PRENTICE'S NITRIC ACID PLANT. 41
in the opposite direction. The action of the steam is to decompose the nitre-glycerine. The acids obtained, however, are very weak. By the use of Webb's plant the sulphuric acid may be concentrated to a strength of 95 per cent, and the dilute nitric acid can be brought up to a specific gravity of 1.42.
Tf. Two points in the manufacture of nitro-glycerine are of the greatest importance, viz., the purity of the glycerine used, and the strength and purity of the acids used in the nitration. With regard to the first of these, great care should be taken, and a complete analysis and thorough examination, including a preliminary experi- mental nitration, should always be instituted. As regards the second, the sulphuric acid should not only be strong (96 per cent), but as free from impurities as possible. With the nitric acid, which is generally made at the explosive works where it is used, care must be taken that it is as strong as possible (97 per cent, and upwards). This can easily be obtained if the plant designed by Mr Oscar Guttmann* is used. Having worked Mr Gutt- mann's plant for some time, I can testify as to its value and efficiency.
Another form of nitric acid plant, which promises to be of considerable service to the manufacturer of nitric acid for the purpose of nitrating, is the. invention of Mr Manning Prentice, of Stowmarket. Through the kind- ness of Mr Prentice, I lately visited his works to see the plant in operation. It consists of a still, divided into compartments or chambers in such a manner that the fluid may pass continuously from one to the other. The nitric acid being continuously separated by distillation,
* " The Manufacture of Nitric Acid," Jour. Sac. Chem. Ind., March 1893.
42 NITRO-EXPLOSIVES.
the contents of each division vary — the first containing the full proportion of nitric acid, and each succeeding one less of the nitric acid, until from the overflow of the last one the bisulphate of soda flows away without any nitric acid. The nitrate of soda is placed in weighed quantities in the hopper, whence it passes to the feeder. The feeder is a miniature horizontal pug-mill, which receives the streams of sulphuric acid and of nitrate, and after thoroughly mixing them, delivers them into the still, where, under the influence of heat, they rapidly become a homogeneous liquid, from which nitric acid continuously distils.
Mr Prentice says : " I may point out that while the ordinary process of making nitric acid is one of fractional distillation by time, mine is fractional distillation by space." " Instead of the operation being always at the same point of space, but differing by the successive points of time, I arrange for the differences to take place at different points of space, and these differences exist at one and the same points of time." It is possible with this plant to produce the full product of nitric acid of a gravity of 1.500, or to obtain the acid of varying strengths from the different still-heads. One of these stills, capable of producing about 4 tons of nitric acid per week, weighs less than 2 tons. It is claimed that there is by their use a saving of more than two-thirds in fuel, and four-fifths in condensing plant Further particulars and illustrations will be found in Mr Prentice's paper (Journal of the Society of Chemical Industry, 1894, P- 323>
CHAPTER III. DYNAMITE AND GELATINES.
Kieselguhr Dynamite — Classification of Dynamites — Properties and Efficiency of Ordinary Dynamite— Other Forms of Dynamite — Gelatine and Gelatine Dynamites, Suitable Gun-Cotton for, and Treatment of — Other Materials used — Composition of Gelignite— Blasting Gelatine — Gelatine Dynamite — Absorbing Materials — Wood Pulp — Potassium Nitrate, &c. — Manufacture and Apparatus used, and Properties of Gelatine Dynamites — Cordite— Composition and Manufacture.
Dynamite. — Dynamite consists of nitro-glycerine either absorbed by some porous material, or mixed with some other substance or substances which are either explosives or merely inert materials. Among the porous substances used is kieselguhr, a silicious earth which consists chiefly of the skeletons of various species of diatoms. This earth occurs in beds chiefly in Hanover, Sweden, and Scotland. The best quality for the purpose of manufacturing dynamite is that which contains the largest quantity of the long tubular bacillarice, and less of the round and lancet-shaped forms, such as pleuro- sigmata and dictyochece, as the tube-shaped diatoms absorb the nitro-glycerine better, and it becomes packed into the centre of the silicious skeleton of the diatoms, the skeleton acting as a kind of tamping, and increasing the intensity of the explosion.
Dynamites are classified by the late Colonel Cundill, R.A., in his " Dictionary of Explosives " as follows : —
i. Dynamites with an inert base, acting merely as an absorbent.
44 NITRO-EXPLOSIVES.
2. Dynamites with an active base, i.e., an explosive base. No. 2 may be again divided into three minor classes, which contain as base —
(a.) Charcoal.
(£.) Gunpowder or other nitrate, or chlorate mixture.
(c.) Gun-cotton or other nitro compound (nitro- benzol, &c.).
The first of these, viz., charcoal, was one of the first absorbents for nitro-glycerine ever used ; the second is represented by the well-known Atlas powder; and the last includes the well-known and largely used gelatine compounds, viz., gelignite and gelatine dynamite, and also tonite No. 3, &c.
In the year 1867 Nobel produced dynamite by absorbing the nitro-glycerine in an inert substance, form- ing a plastic mass. In his patent he says : " This invention relates to the use of nitro-glycerine in an altered condition, which renders it far more practical and safe for use. The altered condition of the nitro-glycerine is effected by causing it to be absorbed in porous un- explosive substances, such as charcoal, silica, paper, or similar materials, whereby it is converted into a powder, which I call dynamite, or Nobel's safety powder. By the absorption of the nitro-glycerine in some porous substance it acquires the property of being in a high degree insensible to shocks, and it can also be burned over a fire without exploding."
Ordinary dynamite consists of a mixture of 75 per cent, of nitro-glycerine and 25 per cent, of kieselguhr. The guhr as imported (Messrs A. Haake & Co. are the chief importers) contains from 20 to 30 per cent, of water and organic matter. The water may be very easily estimated by drying a weighed quantity in a platinum crucible at 100° C. for some time and reweighing, and the
PREPARATION OF THE KIESELGUHR. 45
organic matter by igniting the residue strongly over a Bunsen burner. Before theguhr can be used for making dynamite it must be calcined, in order not only to get rid of moisture, but also the organic matter.
A good guhr should absorb four times its weight of nitro-glycerine, and should then form a comparatively dry mixture. It should be pale pink, red brown, or white. The pink is generally preferred, and it sh.ould be as free as possible from grit of all kinds, quartz particles, &c., and should have a smooth feeling when rubbed between the finger and thumb, and should show a large quantity of diatoms when viewed under the microscope. The following was the analysis of a dried sample of kiesel- guhr :— Silica, 94.30; magnesia, 2.10 ; oxide of iron and alumina, 1.3; organic matter, 0.40; moisture, 1.90 percent.
The guhr is generally dried in a reverberatory muffle furnace. It is spread out on the bottom to the thick- ness of 3 or 4 inches, and should every now and then be turned over and raked about with an iron rabble or hoe. The temperature should be sufficiently high to make the guhr red hot, or the organic matter will not be burnt off. The time occupied in calcining will depend of course upon the quality of the guhr being operated upon. Those containing a high percentage of water and organic matter will of course take longer than those that do not. A sample of the calcined guhr should not contain more than 0.5 per cent, of moisture and organic matter together.
After the guhr is dry it requires to be sifted and crushed. The crushing is done by passing it between iron rollers fixed at the bottom of a cone or hopper, and revolving at a moderate speed. Beneath the rollers a fine sieve should be placed, through which the guhr must be made to pass.
(
46 NITRO-EXPLOSIVES.
The kieselguhr having been dried, crushed, and sifted, should be packed away in bags, and care should be taken that it does not again absorb moisture, as/if it f contains anything above about five-tenths per cent of I water it will cause the dynamite made with it to exude, guhr thus prepared is taken up to the danger area, and mixed with nitro-glycerine. The nitro-glycerine used should be quite free from water, and clear, and should have been standing for a day or two in the pre- cipitating house. The guhr and nitro-glycerine are mixed in lead tanks (about ij feet deep, and 2 to 3 feet long), in the proportions of 75 of the nitro- glycerine to 25 of the guhr, unless the guhr is found to be too absorbent, which will cause the dynamite to be too dry and to crumble. In this case a small quantity of barium sulphate, say about I per cent., should be added to the guhr. This will lessen its absorbing powers, or a highly absorptive sample of guhr may be mixed with one of less absorptive power, in the propor- tions found by experiment to be the best suited to make a fairly moist dynamite, but one that will not exude.
The mixing itself is generally performed in a separate house. In a series of lead-lined tanks the guhr is weighed, placed in a tank, and the nitro-glycerine poured on to it. The nitro-glycerine may be weighed out in incliarubbcr buckets. The whole is then mixed by hand, and well rubbed between the hands, and afterwards passed through a sieve. At this stage the dynamite should be dry and powdery, and of a uniform colour.
It is now ready to be made up into cartridges, and should be taken over to the cartridge huts. These are small buildings surrounded with mounds, and con- tain a single cartridge machine. Each hut requires three girls — one to work the press, and two to wrap up the
PACKING DYNAMITE. 47
cartridges. The cartridge press consists of a short cylinder of the diameter of the cartridge that it is in- tended to make. Into this cylinder a piston, pointed with ivory or lignum vitae wood, works up and down from a spring worked by a lever. Round the upper edge of the cylinder is fastened a canvas bag, into which the powdery dynamite is placed by means of a wooden scoop, and the descending piston forces the dynamite down the cylinder and out of the open end, where the compressed dynamite can be broken off at convenient lengths. The whole machine should be made of gun- metal, and should be upright against the wall of the building. The two girls, who sit at tables placed on each side of the press, wrap the cartridges in parchment paper. From these huts the cartridges are collected by boys every ten minutes or a quarter of an hour, and taken to the packing room, where they are packed in 5 Ib. card- board boxes, which are then further packed in deal boxes lined with indiarubber, and fastened down air tight. The wooden lids are then nailed down with brass or zinc nails, and a label pasted on the outside giving the weight and description of the contents. The boxes should then be removed to the magazines. It is well to take a certain number of cartridges from the packing house at different times during the day, say three or four samples, and to test them by the heat test. A sample cut from a cartridge, about I inch long, should be placed under a glass shade, together with water (a large desiccator, in fact), and left for some days. A good dynamite should not, under these conditions, show any signs of exudation, even after weeks.*
* For analysis of dynamite, sec chapter on " Analysis," and author's article in Chem, Neivs, 23rd September 1892.
i, UNIVERSITY
f»C
48 NITRO-EXPLOSIVES.
Properties of Kieselguhr Dynamite. — One cubic foot of dynamite weighs 76 Ibs. 4 oz. The specific gravity of 75 per cent dynamite is, however, 1.50. It is a red or grey colour, and rather greasy to the touch. It is much less sensitive to shock than nitro-glycerine, but explodes occasionally with the shock of a rifle bullet, or when struck. The addition of a few per cent, of camphor will considerably diminish its explosive qualities to such an extent that it can be made non-explosive except to a very strong fulminate detonator. The direct contact of water disintegrates dynamite, separating the nitro- glycerine, hence great caution is necessary in using it in wet places. It freezes at about 40° Fahr., and remains frozen at temperatures considerably exceeding that point. When frozen, it is comparatively useless as an explosive agent, and must be thawed with care. This is best done by placing the cartridges in a warming pan, which con- sists of a tin can, with double sides and bottom, into which hot water (130° Fahr.) can be poured. The dyna- mite will require to be left in for some considerable time before it becomes soft. On no account must it be placed on a hot stove or near a fire, as many serious accidents have occurred in this way.
Frozen dynamite is a hard mass, with altered pro- perties, and requires 1.5 grm. of fulminate instead of 0.5 grm. to explode it. Thawing may also cause exuda- tion of the nitro-glycerine, which is much more sensitive to shock, and if accidentally struck with an iron tool, may explode. It is a dangerous thing to cut a frozen cartridge with a knife. Ramming is even more dangerous ; in fact it is not only dangerous, but wasteful, to use dynamite when in a frozen state.
Dynamite explodes at a temperature of 360° Fahr., and is very sensitive to friction when hot In hot
PROPERTIES OF ORDINARY DYNAMITE. 49
countries it should never be exposed to the rays of the I sun. It should, however, not be kept in a damp or moist / place, as this is liable to cause exudation. Sunlight, if / direct, can cause a slow decomposition, as with all nitro/ and nitric compounds. Electric sparks ignite, without/ exploding it, at least when operating in the open air.
Dynamite, when made with neutral nitro-glycerine, appears to keep indefinitely. Sodium or calcium car- bonate to the extent of I per cent, is often added to dynamite to ensure its being neutral. If it has commenced to undergo change, however, it rapidly becomes acid, and sometimes explodes spontaneously, especially if contained in resisting envelopes. Nevertheless, neutral and well- made dynamite has been kept for years in a magazine without loss of its explosive force. If water is brought into contact with it, the nitro-glycerine is gradually dis- placed from the silica (guhr). This action tends to renderj all wet dynamite dangerous.
It has been observed that a dynamite made with wood j sawdust can be moistened and then dried without marked I alteration, and from 15 to 20 per cent, of water may be I added to cellulose dynamite without depriving it of the/ power of exploding by strong detonator (this is similar! to wet gun-cotton). It is, however, rendered much less\ sensitive to shock. With regard to the power of No. I dynamite, experiments made in lead cylinders give the relative value of No. I dynamite, i.o; blasting gelatine, 1.4; and nitro-glycerine, 1.4. The heat vibrated by the sudden explosion of dynamite is the same as its heat of combustion,* and proportionate to the weight of nitro- glycerine contained in the mixture. The gases formed are carbonic acid, water, nitrogen, and oxygen.
* Berthelot, " Explosives and their Power." D
5<D NITKOEXPLOSIVES.
The " explosive wave " (of Berthelot) for dynamite is about 5,000 metres per second. At this rate the explosion of a cartridge a foot long would only occupy ^Joo part of a second, while a ton of dynamite cartridges about 1 diameter, laid end to end, and measuring one mile in length, would be exploded in one-quarter of a second by detonating a cartridge at either end.* Mr C. Napier Hake, F.I. C., the Inspector of Explosives for the Victorian Government, in his paper, " Notes on Explosives," says : " The theoretical efficiency of an explosive cannot in 1 practice be realised in useful work for several reasons, as for instance in blasting rock —
" i. Incomplete combustion.
" 2. Compression and chemical changes induced in surrounding material.
" 3. Energy expended in cracking and heating of the material which is not displaced.
" 4. The escape of gas through the blast-hole and the fissures caused by the explosion.
" The useful work consists partly in displacing the shattered masses. The proportion of useful work obtain- able has been variously estimated at from 14 to 33 per cent, of the theoretical maximum potential."
Among the various forms of dynamite that are manufactured is carbo-dynamite, the invention of Messrs Walter F. Reid and W. D. Borland. The base is nitro- glycerine, and the absorbent is carbon in the form of burnt cork. It is as cheap as ordinary dynamite, and has greater explosive force, seeing that 90 per cent, of the mixture is pure nitro-glycerine, and the absorbent itself is highly combustible. It is also claimed that if this dynamite becomes wet, no exudation takes place.
* C. N. Hake, "Notes on Explosives," Jour. Soc. Chem. Ind., 1889.
BLASTING GELATINE AND GELATINE DYNAMITE. 51
Atlas powder is a dynamite, chiefly manufactured in America at the Repanno Chemical Works, Philadelphia. It is a composition of nitro-glycerine, wood-pulp, nitrate of soda, and carbonate of magnesia. This was the explo- sive used in the outrages committed in London, by the so- called " dynamiters." Different varieties contain from 20 to 75 per cent, of nitro-glycerine.
The Rhenish dynamite, considerably used in the mines of Cornwall, is composed of 70 parts of a solution of 2 to 3 per cent, of naphthaline in nitro-glycerine, 3 parts of chalk, 7 parts of sulphate of barium, and 20 of kieselguhr.
Kieselguhr dynamites are being largely given up in f favour of gelatine explosives. The late Colonel Cundill, / / / in his " Dictionary of Explosives," gives a list of about 125 kinds of dynamites. Many of these, however, are not manufactured. Among the best known after the ordinary No. I dynamite, are forcite, ammonia dynamite, litho- fracteur, rendrock, Atlas powder, giant powder, and the various explosive gelatines. They all contain nitro- glycerine, mixed with a variety of other substances, such as absorbent earths, wood-pulp, nitro-cotton, carbon in some form or other, nitro-benzol, paraffin, sulphur, nitrates, or chlorates, &c., &c.
Blasting Gelatine and Gelatine Dynamite. — The
gelatine explosives chiefly in use are known under the names of blasting gelatine, gelatine dynamite, and gelignite. They all consist of the variety of nitro- cellulose known as collodion-cotton, i.e., a mixture of the penta- and tetra-nitrates, dissolved in nitro-glycerine, and made up with various proportions of wood-pulp, and some nitrate, or other material of a similar nature. As the gun-cotton contains too little oxygen for complete
52 NITRO-EXPLOSIVES.
combustion, and the nitro-glycerine an excess, a mixture of the two substances is very beneficial.
Blasting gelatine consists of collodion-cotton and nitro-glycerine without any other substance, and was patented by Mr Alfred Nobel in 1875. It is a clear, semi-transparent, jelly-like substance, of a specific gravity of 1.5 to 1.55, slightly elastic, resembling indiarubber, and generally consists of 92 per cent, to 93 per cent, of nitro-glycerine, and 7 to 8 per cent, of nitro-cotton. The cotton from which it is made should be of good quality. The following is the analysis of a sample of nitro-cellulose which made very good gelatine : —
Soluble cotton 99.1 18 per cent. Gun-cotton - 0.642 „
Non-nitrated cotton 0.240 „
Nitrogen 11.64 »
Total ash 0.25 „
The soluble cotton, which is a mixture of the tetra- and penta-nitrates is soluble in ether-alcohol, and also in nitro-glycerine, and many other solvents, whereas the hexa - nitrate (gun-cotton), C12H14O4(ONO2)6, is not soluble in the above liquids, although it is soluble in acetone or acetic ether. It is very essential, therefore, that the nitro-cotton used in the manufacture of the gelatine explosives should be as free as possible from gun-cotton, otherwise little lumps of undissolved nitro- cotton will be left in the finished gelatine. The non- nitrated or unconverted cotton should also be very low, in fact considerably under J per cent.
The nitro-cotton and the nitro-glycerine used should always be tested before use by the heat test, because if they do not separately stand this test, it cannot be expected that the gelatine made from them will do so. It often occurs, however, that although both the in-
THE NITRO-COTTON USED FOR GELATINE. 53
gradients stand this test separately before being mixed, that after the process of manufacture one or other or both fail to do so.
The nitro-cotton most suitable for gelatine making is that which has been finely pulped. If it is not already fine enough, it must be passed through a fine brass wire sieve. It will be found that it requires to be rubbed through by hand, and will not go through at all if in the least degree damp. It is better, therefore, to dry it first. The percentage of nitrogen in the nitrated cotton should be over 1 1 percent. It should be as free as possible from sand or grit, and should give but little ash upon ignition, not more than 0.25 per cent. The cotton, which is generally packed wet in zinc-lined wooden boxes, will require to be dried, as it is very essential indeed that none of the materials used in the manufacture of gelatine should contain more than the slightest trace of water. If they do, the gelatine subsequently made from them will most certainly exude, and become dangerous and comparatively valueless. It will also be much more difficult to make the nitro-cotton dissolve in the nitro- glycerine if either contains water.
In order to find out how long any sample of cotton requires to be dried, a sample should be taken from the centre of several boxes, well mixed, .and about 1,000 grms. spread out on a paper tray, weighed, and the whole then placed in the water oven at ioo°C, and dried for an hour or so, and again weighed, and the percentage of moisture calculated from the loss in weight. This will be a guide to the time that the cotton will probably require to be in the drying house. Samples generally contain from 20 to 30 per cent, of water. After drying for a period of forty-eight hours, a sample should be again dried in the oven at 100° C, and the moisture
54 NITRO-EXPLOSIVES.
determined, and so on at intervals until the bulk of the cotton is found to be dry, i.e., to contain from 0.25 to 0.5 per cent of moisture. It is then ready to be sifted. During the process of removing to the sifting house and the sifting itself, the cotton should be exposed to the* air as little as possible, as dry nitro-cotton absorbs as much as 2 per cent, of moisture from the air at ordinary temperatures and average dryness.
The drying house usually consists of a wooden building, the inside of which is fitted with shelves, or rather framework to contain drawers, made of wood, with brass or copper wire netting bottoms. A current of hot air is made to pass through the shelves and over the surface of the cotton, which is spread out upon them to the depth of about 2 inches. This current of air can be obtained in any way that may be found convenient, such as by means of a fan or Root's blower, the air being passed over hot bricks, or hot-water pipes before entering the building. The cotton should also be occasionally turned over by hand in order that a fresh surface may be continually exposed to the action of the hot air. The building itself may be heated by means of hot-water pipes, but on no account should any of the pipes be exposed. They should all be most carefully covered over with wood-work, because when the dry nitro-cotton is moved, as in turning it over, very fine particles get into the air, and gradually settling on the pipes, window ledges, &c., may become very hot, when the slightest friction might cause an explosion. It is on this account that this house should be very carefully swept out every day. It is also very desirable that the floor of this house should be covered with oilcloth or linoleum, as being soft, it lessens the friction.
List shoes should always be worn in this building,
COMPOSITION OF GELATINE COMPOUNDS. 55
and a thermometer hung up somewhere about the centre of the house, and one should also be kept in one of the trays to give the temperature of the cotton, especially the bottom of the trays. The one nearest to the hot air inlet should be selected. If the temperature of the house is kept at about 40° C. it will be quite high enough. The building must of course be properly venti- lated, and it will be found very useful to have the walls made double, and the intervening space filled with cinders, and the roof covered with felt, as this helps to prevent the loss of heat through radiation, and to preserve a uniform temperature, which is very desirable.
The dry cotton thus obtained, if not already fine enough, should be sifted through a brass sieve, and packed away ready for use in zinc air-tight cases, or in indiarubber bags. The various gelatine compounds, gelignite, gelatine dynamite, and blasting gelatine, are manufactured in exactly the same way. The forms known as gelatine dynamite differ from blasting gelatine in containing certain proportions of wood-pulp and potassium nitrate, &c. The following are analyses of some typical samples of the three compounds : —
|
Gelatine |
Blasting |
||
|
Gelignite. |
Dynamite. |
Gelatine. |
|
|
Nitro-glycerine |
60.514 |
71.128 |
92.94 per cent. |
|
Nitro-cellulose |
4.888 |
7.632 |
7.06 „ |
|
Wood-pulp - |
7.178 |
4.259 |
„ |
|
Potassium nitrate |
- 27.420 |
16.720 |
„ |
|
Water - |
- |
0.26l |
... |
The gelignite and gelatine dynamites consist, there- fore, of blasting gelatine, thickened up with a mixture of absorbing materials. Although the blasting gelatine is weight for weight more powerful, it is more difficult to make than either of the other two compounds, it being somewhat difficult to make it stand the exudation and
56 NITROEXPLOSIVES.
melting tests. The higher percentage of nitro-cotton, too, makes it expensive.
When the dry nitro-cotton, which has been carefully weighed out in the proportions necessary either for blasting gelatine or any of the other gelatine explosives, is brought to the gelatine making house, it is placed in a lead-lined trough, and the necessary quantity of pure dry nitro-glycerine poured upon it. The whole is then well stirred up, and kept at a temperature of from 40° to 45° C. It should not be allowed to go much above 40° C. ; but higher temperatures may be used if the nitro- cotton is very obstinate,* and will not dissolve. Great caution must, however, be observed in this case. The mixture should be constantly worked about by the workman with a wooden paddle for at least half an hour. At a temperature of 40° to 45° the nitro-glycerine acts upon the nitro-cotton and forms a jelly. Without heat the gelatinisation is very imperfect indeed, and at tem- peratures under 40° C. takes place very slowly. The limit of temperature is 50° C. or thereabout. Beyond this the jelly should never be allowed to go, and to 50° only under exceptional circumstances.
The tank in which the jelly is made is double lined, in order to allow of the passage of hot water between its inner and outer linings. A series of such tanks are generally built in a wooden framework, and the double linings are made to communicate, so that the hot water can flow from one to the other consecutively. The tem- perature of the water should be about 60° C. if it is intended to gelatinise at 45° C., and about 80° if at 50° C. ; but this point must, of course, be found by ex- periment for the particular plant used. An arrangement
* Generally due to the nitro-cotton being damp.
MIXING THE JELLY WITH WOOD PULP, ETC. 57
should be made to enable the workman to at once cut off the supply of hot water and pass cold water through the tanks in case the explosive becomes too hot.
FIG. ga. — MIXING MACHINE. H, Reversing Handle; L, Handle to tip up Mixer ; £, Dividing Belts.
The best way to keep the temperature of the water constant is to have a large tank rv TL.J. 20 e. of water raised upon a platform, — -^ some 5 or 6 feet high, outside the building, which is automatically supplied with water, and into which steam is turned. A thermometer stuck through a piece of cork and floated upon the surface of the tank will give the means of regulating the temperature. MlXER-
When the jelly in the tanks has become semi-
58 NITRO-EXPLOSIVES.
transparent, and the cotton has entirely dissolved, the mixture should be transferred to a mixing machine. An ordinary bread-kneading machine does very well. It must, of course, be made of gun-metal or phosphor bronze. There must be no iron about the working parts, and the bearings must be carefully looked to.
FIG. io<*.— MR M'RoBERTs' FORM OF MIXER FOR GELATINE EXPLOSIVES.
A suitable masticating machine for this purpose is supplied by Messrs Werner & Pfleiderer of London (Fig. 9), or George M'Roberts'* machine (Fig. 10, a and ft)
* Seejmtr. Soc. Chem. Ind., 1890, 267.
MIXING MACHINES.
59
may be used. This latter is the form of mixer that is used at Nobel's factories.
If it is intended to make gelignite, or gelatine
0L_ Ufa
wr
FIG. T.ob. — PLAN OF THE Box CONTAINING THE EXPLOSIVE, IN M 'ROBERTS' MACHINE.
dynamite, it is at this point that the proper proportions of wood-pulp* and potassium nitrate should be added,
* Most of the wood-pulp used in England is obtained from pine- trees, but poplar, lime, birch, and beech wood is also used. It is chiefly imported as wood-pulp. The pulp is prepared as follows : — The bark and roots are first removed, and the logs then sawn into boards, from which the knots are removed. The pieces of wood are afterwards put through a machine which breaks them up into small pieces about an inch long, which are then crushed between rollers. These fragments are finally boiled with a solution of sodium bisul- phite, under a pressure of about 90 Ibs. per square inch, the duration of the boiling being from ten to twelve hours. Sulphurous acid has also been used. Pine-wood yields about 45 per cent, and birch about 40 per cent, of pulp when treated by this process. The pulp is afterwards bleached and washed, &c. The following analysis of woods are by Dr H. Miiller : —
Birch. Beech. Lime. Pine. Poplar.
Cellulose - 55-52 45.47 53.09 56.99 62.77 Per cent.
Resin - - 1.14 0.41 3.93 0.97 1.37 „
Aqueous extract 2.65 2.47 3.56 1.26 2.88 „
Water 12.48 12.57 10.10 13.87 12.10 „
Lignine - 28.21 39.14 29.32 26.91 20.88 „
60 NITRO-EXPLOSIVES.
and the whole well mixed for at least half an hour, until the various ingredients are thoroughly incorporated. These mixing machines can either be turned by hand, or a shaft can be brought into the house and the machine worked by means of a belt at twenty to thirty revolu- tions per minute. The bearings should be kept con- stantly greased and examined, and the explosive mixture carefully excluded. When the gelatine mixture has been thoroughly incorporated, and neither particles of nitrate or wood meal can be detected in the mass, it should be transferred to wooden boxes and carried away to the cartridge-making machines to be worked up into cartridges.
The application of heat in the manufacture of the jelly from collodion-cotton and nitro-glycerine is abso- lutely necessary, unless some other solvent is used besides the nitro-glycerine, such as acetone, acetic ether, methyl, or ethyl alcohol. (They are all too expensive, with the exception of acetone and methyl alcohol, for use upon the large scale.) These liquids not only dissolve the nitro-cellulose in the cold, but render the resulting gelatine compound less sensitive to concussion, and reduce its quickness of explosion (as in cordite). They also lower the temperature at which the nitro- glycerine becomes congealed, i.e., they lower the freezing point* of the resulting gelatine.
The finished gelatine paste, upon entering the car- tridge huts, is at once transferred to the cartridge-making machine, which is very like an ordinary sausage-making machine-f- (Fig. 1 1). The whole thing must be made of gun-metal or brass, and it consists of a conical case con-
* It has been proposed to mix dynamite with amyl alcohol for this purpose.
t G. M 'Roberts, /<wr. Soc. Chcm. Ind., 3ist March 1890, p. 266.
CARTRIDGE-MAKING MACHINE.
6l
taining a shaft and screw. The revolutions of the shaft causes the thread of the screw to push forward the gelatine introduced by the hopper on the top to the nozzle, the apex of the cone-shaped case, from whence the gelatine issues as a continuous rope. The nozzle is of course of a diameter according to the size of cartridge required.
The issuing gelatine can of course be cut off at any length. This is best done with a piece of hard wood planed down to a cutting edge, i.e., wedge-shaped. Mr Trench has devised a kind of brass frame, into which the gelatine issuing from the nozzle of the cartridge machine is forced, finding its way along a series of grooves. When the frame is full, a wooden frame, which is hinged
FIG. ii.— CARTRIDGE-MAKING MACHINE FOR GELATINE EXPLOSIVES.
to one end of the bottom frame, and fitted with a series of brass knives, is shut down, whereby cut.ting the gelatine up into lengths of about 4 inches.
It is essential that the cartridge machines should have no metallic contacts inside. The bearing for the screw shaft must be fixed outside the cone containing the gelatine. One of these machines can convert from 5 to 10 cwt. of gelatine into cartridges per diem, depend- ing upon the diameter of the cartridges made.
After being cut up into lengths of about 3 inches, the gelatine is rolled up in cartridge paper. Waterproof
62 NITRO-EXPLOSIVES.
paper is generally used. The cartridges are then packed away in cardboard boxes, which are again packed in deal boxes lined with indiarubber, and screwed down air tight, brass screws or zinc or brass nails being used for the purpose. These boxes are sent to the magazines. Before the boxes are fastened down a cartridge or so should be removed and tested by the heat test, the liquefaction test, and the test for liability to exudation. (Appendix, p. 6, Explosives Act, 1875.) A cartridge also should be stored in the magazine in case of any subsequent dispute after the bulk of the material has left the factory.
The object of the liquefaction test is to ensure that the gelatine shall be able to withstand a fairly high tem- perature (such as it might encounter in a ship's hold) without melting or running together. The test is carried out as follows : — A cylinder of the gelatine dynamite is cut from the cartridge of a length equal to its diameter. The edges must be sharp. This cylinder is to be placed on end on a flat surface (such as paper), and secured by a pin through the centre, and exposed for 144 consecutive hours to a temperature of 85° to 90° F., and during such time the cylinder should not diminish in height by more than one-fourth of an inch, and the cut edges should remain sharp. There should also be no stain of nitro- glycerine upon the paper.
The exudation test consists in freezing and thawing the gelatine three times in succession. Under these conditions there should be no exudation of nitro- glycerine. All the materials used in the manufacture of gelatine explosives should be subjected to analytical examination before use, as success largely depends upon the purity of the raw materials. The wood-pulp, for instance, must be examined for acidity.
RP '
*
or THE
PROPERTIES OF THE GELATINE EXPLOSIVES. 63
Properties of the Gelatine Compounds. — Blast- ing gelatine is generally composed of 93 to 95 parts nitro-glycerine, and 5 to 7 parts of nitro- cellulose, but the relative proportions of explosive base and nitro-glycerine, &c., in the various forms of the gelatine explosives do not always correspond to those necessary for total combustion, either because an in- complete combustion gives rise to a greater volume of gas, or because the rapidity of decomposition and the law of expansion varies according to the relative pro- portions and the conditions of application. The various additions to blasting gelatine generally have the effect of lowering the strength by reducing the amount of nitro-glycerine, but this is sometimes done in order to change a shattering agent into a propulsive force. If this process be carried too far, we of course lose the advantages due to the presence of nitro-glycerine. There is therefore a limit to these additions.*
The homogeneousness and stability of the mixture are of the highest "importance. It is highly essential that the nitro-glycerine should be completely absorbed by the substances with which it is mixed, and that it should not subsequently exude when subjected to heat or damp. It is also important that there should be no excess of nitro-glycerine, as this may diminish instead of augment the strength, owing to a difference in the mode of the propagation of the explosive wave in the liquid and in the mixture. Nitro-glycerine at its freezing point has a tendency to separate from its absorbing material, in fact to exude. When frozen, too, it requires a more powerful detonation to explode it, but it is less sensitive to shock.
* Mica is said to increase the rapidity of explosion when mixed with gelatine.
64 NITKO-EXPLOSIVES.
The specific gravity of blasting gelatine is 1.5 (*>., nearly equal to that of nitro-glycerol) ; that of gun-cotton (dry) is i.o.
Blasting gelatine burns in the air when unconfined without explosion, at least in small quantities and when not previously heated, but it is rather uncertain in this respect. It can be kept at a moderately high tempera- ture (70° C.) without decomposition. At higher tem- peratures the nitro-glycerine will partially evaporate. When slowly heated, it explodes at 204° C. If, however, it contains as much as 10 per cent, of camphor, it burns without exploding. According to Berthelot,* gelatine composed of 91.6 per cent, nitro-glycerine and 8.4 per cent. of nitro-cellulose, which are the proportions correspond- ing to total combustion, produces by explosion I77CO2
He takes C24H22(NO3H)0On as the formula of the nitro-cellulose, and 5iC3H2(NO3H)3 + C24H22(NO3H)0O11 as the formula of the gelatine itself, its equivalent weight being 12,360 grms. The heat liberated by its explosion is equal to 19,381 calories, or for I kilo. 1,535 calories. Volume of gases reduced temperature equals 8,950 litres. The relative value •)• of blasting gelatine to nitro-glycerine is as 1.4 to 1.45, kieselguhr dynamite being taken as i.o.
Cordite. — The British smokeless powder, cordite, is the patent of Sir F. A. Abel and Professor Devvar, and is somewhat similar to blasting gelatine. It is chiefly manufactured at the Royal Gunpowder Factory at Waltham Abbey, but also at one or two private factories. It consists of gun-cotton, 37 per cent; nitro-glycerine, 58
* Berthelot, " Explosives and their Powers." t Roux and Sarrau.
MANUFACTURE OF CORDITE. 65
per cent. ; and vaseline, 5 per cent. The gun-cotton used is the hexa-nitrate, which is not soluble in nitro-glycerine. It is therefore necessary to use some solvent such as acetone, in order to form the jelly with nitro-glycerine.
The process of manufacture of cordite is very similar, as far as the chemical part of the process is concerned, to that of blasting gelatine, and is briefly as follows : — The gun-cotton is first dried in the form of p-oz. primers down to about I per cent, of moisture ; 27f Ibs. are then placed in a brass-lined box, and 43 J Ibs. of nitro-glycerine are carefully added ; the whole is then mixed by hand, and afterwards taken to the incorporating machine, and thoroughly mixed. During the mixing, 15^- Ibs. of acetone is poured over the charge, and the whole worked into a dough ; 3 J Ibs. of vaseline are also added, and the incorporation continued for seven hours in the form of kneading machine * shown in Fig. 9, which consists of a trough, composed of two halves of a cylinder, in each of which is a shaft which carries a revolving blade. These blades revolve in opposite directions, and one makes about half the number of revolutions of the other. As the blades very nearly touch the bottom of the trough, any material brought into the machine is divided into two parts, kneaded against the bottom, then pushed along -the blade, turned over, and completely mixed. The machine is generally water jacketed, and the top closed in with a glass door, in order to prevent as far as possible the evaporation of the solvent.
When the various ingredients are formed into a
* The incorporating machines of Messrs Werner & Pfleiderer, which are largely used by the manufacturers of smokeless powders, are probably the most perfect ever designed for the purpose.
E
66 NITRO-EXPLOSIVES.
homogeneous mass, the material is taken to the press house, where by means of specially designed presses it is squirted into threads. The plastic mass is pressed into a steel cylinder, at the bottom of which is a small hole, through which it is squirted by means of a plunger or piston pressing on the other end of the cylinder. The cords thus obtained are then wound on a metal drum. Three of these threads are then wound on one drum, and finally six strands are afterwards reeled on a single drum. This is done in order to obtain a uniform blending of the material. With cordite of a larger diameter, the cord is at once cut into lengths of 12 inches. The drums are then taken to the drying house, where the cordite is subjected to a temperature of 100° Fahr. for three to nine days, in order to evaporate off the solvent.
CHAPTER IV. NITRO-CELLULOSE, &c.
Cellulose Properties — Discovery of Gun-Cotton — Properties of Gun-Cotton — Varieties of Soluble and Insoluble Gun-Cottons — Manufacture of Gun-Cotton — Dipping and Steeping — Whirling out the Acid — Washing — Boiling — Pulping — Compressing — The Walthani Abbey Process — Le Bouchet Process — Granulation of Gun-Cotton—Collodion-Cotton Manufacture — Acid Mixture used — Cotton used, &c. — Nitrated Gun- Cotton Tonite — Dangers in Manufacture of Gun-Cotton — Trench's Fire-Extinguishing Compound — Uses of Collodion-Cotton — Celluloid — Manufacture, &c. — Nitro-Starch, Nitro-Jute, and Nitro-Mannite.
The Nitro-Celluloses. — The substance known as cellulose forms the groundwork of vegetable tissues. The cellulose of the woody parts of plants was at one time supposed to be a distinct body, and was called lignine, but they are now regarded as identical. The formula of cellulose is (C6H10O5)X, and it can be ex- tracted in the pure state, from young and tender portions of plants by first crushing them, to rupture the cells, and then extracting with dilute hydrochloric acid, water, alcohol, and ether in succession, until none of these solvents remove anything more. Fine paper or cotton wool yield very nearly pure cellulose by similar treat- ment.
Cellulose is a colourless, transparent mass, absolutely insoluble in water, alcohol, or ether. It is, however, soluble in a solution of cuprammonic solution, prepared from basic carbonate or hydrate of copper and aqueous
68 NITRO-EXPLOSIVES.
ammonia. The specific gravity of cellulose is 1.25 to 1.45. According to Schulze, its elementary composition is expressed by the percentage numbers :—
Carbon 44.0 per cent. 44.2 per cent.
Hydrogen - 6.3 „ 6.4 „
Oxygen 49.7 „ 49.4 ,.
These numbers represent the composition of the ash free cellulose. Nearly all forms of cellulose, however, con- tain a small proportion of mineral matters, and the union of these with the organic portion of the fibre or tissue is of such a nature that the ash left on ignition preserves the form of the original. " It is only in the growing point of certain young shoots that the cellulose tissue is free from mineral constituents" (Hofmeister).
Cellulose is a very inert body. Cold concentrated sulphuric acid causes it to swell up, and finally dissolves it, forming a viscous solution. Hydrochloric acid has little or no action, but nitric acid has, and forms a series of bodies known as nitrates or nitro-celluloses. Cellulose has some of the properties of alcohols, among them the power of forming etherial salts with acids. When cellulose in any form, such as cotton, is brought into contact with strong nitric acid at a low temperature, a nitrate or nitro product, containing nitryl, or the NO9 group, is produced. The more or less complete replace- ment of the hydroxylic hydrogen by NO2 groups depends partly on the concentration of the nitric acid used, partly on the duration of the action. If the most con- centrated nitric and sulphuric acids are employed, and the action allowed to proceed for some considerable time, the highest nitrate, known as hexa-nitro-cellulose or gun-cotton, C12H14O4(O.N(X)6, will be formed; but with weaker acids, and a shorter exposure to their action, the tetra and penta and lower nitrates will be formed.
GUN-COTTON. 69
The discovery of gun-cotton is generally attributed to Schonbein (1846), but Braconnot (in 1832) had previously nitrated starch, and six years later Felouse prepared nitro cotton and various other nitro bodies, and Dumas nitrated paper, but Schonbein was apparently the first chemist to use a mixture of strong nitric and sulphuric acids. Many chemists, such as Piobert in France, Morin in Russia, and Abel in England, studied the subject ; but it was in Austria, under the auspices of Baron Von Lenk, that the greatest progress was made. Lenk used cotton in the form of yarn, made up into hanks, which he first washed in a solution of potash, and then with water, and after drying dipped them in the acids. The acid mixture used consisted of 3 parts by weight of sulphuric to I part of nitric acid, and were prepared some time before use. The cotton was dipped one skein at a time, stirred for a few minutes, pressed out, steeped, and excess of acid removed by washing with water, then with dilute potash, and finally with water. Von Lenk's process was used in England at Faversham (Messrs Hall's Works), but was given up on account of an explosion (1847).
Sir Frederick Abel, working at Stowmarket and Waltham Abbey, introduced several very important improvements into the process, the chief among these being pulping. Having traced the cause of its instability to the presence of substances caused by the action of the nitric acid on the resinous or fatty substances con- tained in the cotton fibre, he succeeded in eliminating them, by boiling the nitro-cotton in water, and by a thorough washing, after pulping the cotton in poachers.
Although gun-cottons are generally spoken of as nitro-celluloses, they are more correctly described as cellulose nitrates, for unlike nitro bodies of other series,
70 NITRO-EXPLOSIVES.
they do not yield, or have not yet done so, amido bodies, on reduction with nascent hydrogen.* The equation of the formation of gun-cotton is as follows :—
2(C6H1005)+6HN03=C12H1404(N03)C+60H2.
Cellulose. Nitric Acid. Gun-Cotton. Water.
The sulphuric acid used does not take part in the re- action, but its presence is absolutely essential to combine with the water set free, and thus to prevent the weaken- ing of the nitric acid. The acid mixture used at Waltham Abbey consists of 3 parts by weight of sulphuric acid of 1.84 specific gravity, and I part of nitric acid of 1.52 specific gravity. The same mixture is also used at Stowmarket (the New Explosive Company's Works). The use of weaker acids results in the formation of collo- dion-cotton and the lower nitrates generally.
The nitrate which goes under the name of gun-cotton is generally supposed to be the hexa-nitrate, and to con- tain 14.14 per cent, of nitrogen ; but a higher percentage than 13.7 has not been obtained from any sample. It is almost impossible (at any rate upon the manufacturing scale) to make pure hexa-nitro-cellulose or gun-cotton ; it is certain to contain several per cents, of the soluble forms, i.e., lower nitrates. It often contains as much as 15 or 1 6 per cent., and only from 13.07"!" to 13.6 per cent, of nitrogen.
A whole series of nitrates of cellulose are supposed to exist, the highest member being the hexa-nitrate, and the lowest the mono-nitrate. Gun-cotton was at one
* " Cellulose," by Cross and Bevan, ed. by W. R. Hodgkinson, p. 9.
t Mr J. J. Sayers, in evidence before the court in the " Cordite Case," says he found 15.2 and 16.1 per cent, soluble cotton, and 13.07 and 13.08 per cent, nitrogen in two samples of Waltham Abbey gun-cotton.
THE NITRO-CELLULOSES. 71
time regarded as the tri-nitrate, and collodion-cotton as the di-nitrate and mono-nitrate, their respective formula being given as follows : —
Mono-nitrocellulose - C(JH9(NO2)O5= 6.763 percent, nitrogen. Di-nitro-cellulose C«H^(NO«)tQ8=II.II „ „
Tri-nitro-cellulose C,5Hr(NO2)3O5= 14.14 „ „
But gun-cotton is now regarded as the hexa-nitrate, and collodion-cotton as a mixture of all the other nitrates. In fact, chemists are now more inclined to divide nitro- cellulose into the soluble and insoluble forms, the reason being that it is quite easy to make a nitro-cellulose entirely soluble in a mixture of ether- alcohol, and yet containing as high a percentage of nitrogen as 12.6; whereas the di-nitrate * should theoretically only contain i i.i I per cent. On the other hand, it is not possible to make gun-cotton with a higher percentage of nitrogen than about 13.7, even when it does not contain any nitro- cotton that is soluble in ether-alcohol. t The fact is that it is not at present possible to make a nitro-cellulose which shall be either entirely soluble or entirely in- soluble, or which will contain the theoretical content of nitrogen to suit any of the above formulae for the cellu- lose nitrates. It is not unlikely that a long series of nitrates exists. It is at any rate certain that whatever strength of acids may be used, and whatever tempera-
* The penta-nitrate CiiHiBO8(NOs)8 =13.75 per cent, nitrogen.
t In the Cordite Trial (1894), Sir F. A. Abel said, "Before 1888 there was a broad distinction between soluble and insoluble nitro-cellulose, collodion-cotton being soluble (in ether-alcohol) and gun-cotton insoluble." Sir H. E. Roscoe, "That he had been unable to make a nitro-cotton with a higher nitrogen content than 13.7." And Prof. G. Lunge said, "Gun-cotton always con- tained soluble cotton, and vice versa:' These opinions were also generally confirmed by Dr E. Frankland, Mr W. Crookes, Dr Armstrong, and others.
72 NITRO-EXPLOSIVES.
ture or other conditions may be present during the nitration, that the product formed always consists of a mixture of the soluble and insoluble nitro-cellulose.
Theoretically too parts of cotton by weight should produce 218.4 parts of gun-cotton, but in practice the yield is a good deal less, both in the case of gun-cotton or collodion-cotton. In speaking of soluble and insoluble nitro-cellulose, it is their behaviour, when treated with a solution consisting of 2 parts ether and I of alcohol, that is referred to. There is, however, another very important difference, and that is their different solubility in nitro- glycerine. The lower nitrates or soluble form is soluble in nitro-glycerine under the influence of heat, a tempera- ture of about 50° C. being required. At lower tem- peratures the dissolution is very imperfect indeed ; and after the materials have been left in contact for days, the threads of the cotton can still be distinguished. The insoluble form or gun-cotton is entirely insoluble in nitro- glycerine. It can, however, be made to dissolve* by the aid of acetone or acetic ether. Both or rather all the forms of nitro-cellulose can be dissolved in acetone or acetic ether. They also dissolve in concentrated sulphuric acid, and the penta-nitrate in nitric acid at about 80° or 90° C.
The penta-nitrate may be obtained in a pure state by the following process, devised by Eder : — The gun-cotton is dissolved in concentrated nitric acid at 90° C., and re- precipitated by the addition of concentrated sulphuric acid. After cooling to o° C., and mixing with a larger volume of water, the precipitated nitrate is washed with :- . water, then with alcohol, dissolved in ether-alcohol, and again precipitated with water, when it is obtained pure.
* Or rather to form a transparent jelly.
THE NITRO-CELLULOSES. 73
This nitrate is soluble in ether-alcohol, and slightly in acetic acid, easily in acetone, acetic ether, and methyl- alcohol, insoluble in alcohol. Strong potash (KOH) solution converts into the di-nitrate C12H18O8(NO3)2. The hexa-nitrate is not soluble in acetic acid or methyl- alcohol.
The lower nitrates known as the tetra- and tri-nitrates are formed together when cellulose is treated with a mixture of weak acids, and allowed to remain in contact with them for a very short time (twenty minutes). They cannot be separated from one another, as they all dis- solve equally in ether-alcohol, acetic ether, acetic acid, methyl-alcohol, acetone, &c.
As far as the manufacture of explosive bodies is con- cerned, the two forms of nitro- cellulose used and manu- factured are gun-cotton or the hexa-nitrate (once regarded as tri-nitro-cellulose), which is also known as insoluble gun- cotton, and the soluble form of gun-cotton, which is also known as collodion, and consists of a mixture of several of the lower nitrates. It is probable that it chiefly consists, however, of the next highest nitrate to gun-cotton, as the theoretical percentage of nitrogen for this body, the penta-nitrate, is 12.75 Per cent, and analyses of com- mercial collodion-cotton, entirely soluble in ether-alcohol, often give as high a percentage as 12.6.
We shall only describe the manufacture of the two forms known as soluble and insoluble, and shall refer to them under their better known names of gun-cotton and collodion-cotton. The following would, however, be the formulae * and percentage of nitrogen of the complete series : —
* Berthelot takes C24H40O20 as the formula of cellulose ; and M. Vieille regards the highest nitrate as (C2iH18(NO3H)nO9). Compt. Rend., 1882, p. 132.
74 NITRO-EXPLOSIVES.
Hexa-nitro-cellulose - - Ci2H14O4(NO3)6 14.14 per cent, nitrogen.
Penta- „ C12H15O5(NO3)5 12.75
Tetra- „ C12H]6Ofi(NO3)4 u.ii
Tri- „ C12H1707(N03)3 9.13 „
Di- „ C12H1808(N03)2 7-65 „
Mono- „ - - C]2H1UO9(NO3) 3.80
Properties of Gun-Cotton. — The absolute density of gun-cotton is 1.5. When in lumps its apparent density is O.I ; if twisted into thread, 0.25 ; when subjected, in the form of pulp, to hydraulic pressure, i.o. Gun-cotton preserves the appearance of the cotton from which it is made. It is, however, harsher to the touch ; it is only slightly hydroscopic (dry gun-cotton absorbs 2 per cent, of moisture from the air). It possesses the property of becoming electrified by friction. It is soluble in acetic ether and acetone, insoluble in water, alcohol, ether, ether-alcohol, methyl-alcohol, &c. It is very explosive, and is ignited by contact with an ignited body, or by shock, or when it is raised to a temperature of 172° C. It burns with a yellowish flame, almost without smoke, and leaves little or no residue. The volume of the gases formed is large, and consists of carbonic acid, carbonic oxide, nitrogen, and water gas. Compressed gun-cotton when ignited often explodes if previously heated to 100° C.
Gun-cotton kept at 80° to 100° C. decomposes slowly, and sunlight causes it to undergo a slow decomposition. It can, however, be preserved for years without under- going any alteration. It is very susceptible to explosions by influence. For instance, a torpedo, even placed at a long distance, may explode a line of torpedoes charged with gun-cotton. The velocity of the propagation of the explosion in metallic tubes filled with pulverised gun-cotton has been found to be from 5,000 to 6,000
PROPERTIES OF GUN-COTTON. 75
mms per second in tin tubes, and 4,000 in leaden tubes (Sebert).
Gun-cotton loosely exposed in the open air burns eight times as quickly as powder (Piobert). A thin disc of gun-cotton may be fired into from a rifle without explosion ; but if the thickness of the disc be increased, an explosion may occur. The effect of gun-cotton in mines is very nearly the same as that of dynamite for equal weights. It requires, however, a stronger detonator, and it gives rise to a larger quantity of carbonic oxide gas. Gun-cotton should be neutral to litmus, and should stand the Government heat test — temperature of 1 50° F. for fifteen minutes (see page 235). In the French navy gun-cotton is submitted to a heat test of 65° C. (= 149° F.) for eleven minutes. It should contain as small a per- centage of soluble nitro -cotton and of non-nitrated cotton as possible.
The products of perfectly detonated gun cotton may be expressed by the following equation :—
2CJ2HU04(NOS)0= r8CO + 6C02 + i4H2O+ I2N.
It does not therefore contain sufficient oxygen for the complete combustion of its carbon. It is for this reason that when used for mining purposes a nitrate is gene- rally added to supply this defect (as, for instance, in tonite). It tends also to prevent the evolution of the poisonous gas, carbonic oxide. The success of the various gelatine explosives is due to this fact, viz., that the nitro- glycerine has an excess of oxygen, and the nitro-cotton too little, and thus the two explosives help one another.
In practice the gases resulting from the explosion of gun-cotton are: — Carbonic oxide, 28.55; carbonic acid, 19.1 1 ; marsh gas (CH4), 11.17; nitric oxide, 8.83 ; nitro- gen, 8.56; water vapour, 21.93 Per cent. The late Mr
76 NITRO-EXPLOSIVES.
E. O. Brown, of Woolwich Arsenal, discovered that per- fectly wet and uninflammable compressed gun-cotton could be easily detonated by the detonation of a priming charge of the dry material in contact with it. This ren- dered the use of gun-cotton very much safer for use as a military or mining explosive.
As a mining explosive, however, gun-cotton is now chiefly used under the form of tonite, which is a mixture of half gun-cotton and half barium-nitrate. This material is sometimes spoken of as " nitrated gun-cotton." The weight of gun-cotton required to produce an equal effect either in heavy ordnance or in small arms is to the weight of gunpowder in the proportion of I to 3, i.e., an equal weight of gun-cotton would produce three times the effect as gunpowder. Its rapidity of combustion, how- ever, requires to be modified for use in firearms. Hence the lower nitrates are generally used, or such compounds as nitro-lignose, nitrated wood, &c., are used.
The initial pressure produced by the explosion of gun- cotton is very large, equal to 18,135 atmospheres, and 8,740 kilogrammes per square centimetre for I kilo., the heat liberated being 1,075 calories (water liquid), or 997.7 cals. (water gaseous), but the quantity of heat liberated changes with the equation of decomposition. According to Berthe- lot,* the heat of formation of collodion-cotton is 696 cals. for 1,053 grms-j or 66i.cals. for I kilo. The heat liber- ated in the total combustion of gun-cotton by free oxy- gen at constant pressure is 2,633 ca^s- f°r M43 gnus., or for I kilo, gun-cotton 2,302 cals. (water liquid), or 2,177 cals- (water gaseous). The heat of decomposition of gun-cotton in a closed vessel, found by experiment at a low density of charge (0.023), amounts to 1,071 cals.
* "Explosives and their Power," trans, by Hake and M'Nab.
MANUFACTURE OF GUN-COTTON. 77
for I kilo, of the substance, dry and free from ash. To obtain the maximum effect of gun-cotton it must be used in a compressed state, for the initial pressures are thereby increased. Wet gun-cotton is much less sensitive to shock than dry. Paraffin also reduces its liability to explode, so also does camphor.
The substance known as celluloid, a variety of nitro- cellulose nearly corresponding to the formula C24H24 (NO3H)8O12, to which camphor and various inert sub- stances are added, so as to render it non-sensitive to shock, may be worked with tools, and turned in the lathe in the same manner as ivory, instead of which material celluloid is now largely used for such articles as knife handles, combs, &c. Celluloid is very plastic when heated towards 150° C, and tends to become very sensitive to shock, and in large quantities might become explosive during a fire, owing to the general heating of the mass, and the consequent evaporation of the camphor. When kept in the air bath at 135° C., celluloid decomposes quickly. In an experiment (made by M. Berthelot) in a closed vessel at 135° C., and the density of the charge being 0.4, it ended in exploding, developing a pressure of 3,000 kilos. A large package of celluloid combs also ex- ploded in the guard's van on one of the German railways a few years ago. Although it is not an explosive under ordinary circumstances, or even with a powerful detonator, considerable care should be exercised in its manufacture.
The Manufacture of Gun-Cotton. — The method used for the manufacture of gun-cotton is that of Abel (Spec. No. 1 102, 20. 4. 65). It was worked out chiefly at Stowmarket* and Waltham Abbey ,f but has in the
* The New Explosive Co. Works. t Royal Gunpowder Factory.
78 NITRO-EXPLOSIVES.
course of time undergone several alterations. These modifications have taken place, however, chiefly upon the Continent, and relate more to the apparatus and machinery used than to any alteration in the process itself. The form of cellulose used is cotton-waste,* which consists of the clippings and waste material from cotton mills. After it has been cleaned and purified from grease, oil, and other fatty substances by treatment with alkaline solutions, it is carefully picked over, and every piece of coloured cotton-rag or string carefully removed. The next operation to which it is submitted has for its object the opening up of the material. For this purpose it is put through a carding machine, and afterwards through a cutting machine, whereby it is reduced to a state suitable for its subsequent treatment with the acids, that is, it has been cut into short lengths, and the fibres opened up and separated from one another.
Drying the Cotton. — This operation is performed in either of two ways. The cotton may either be placed upon shelves in a drying house, through which a current of hot air circulates, or dried in steam-jacketed cylinders. It is very essential that the cotton should be as dry as
* Costs from ^10 to ^25 a ton. In his description of the " Preparation of Cotton-waste for the Manufacture of Smokeless Powder," A. Hertzog states that the German military authorities require a cotton which when thrown into water sinks in two minutes ; when nitrated, does not disintegrate ; when treated with ether, yields only 0.9 per cent, of fat ; and containing only traces of chlorine, lime, magnesia, iron, sulphuric acid, and phosphoric acid. If the cotton is very greasy, it must be first boiled with soda-lye under pressure, washed, bleached with chlorine, washed, treated with sulphuric acid or HC1, again washed, centrifugaled, and dried ; if very greasy indeed a preliminary treatment with lime-water is desirable. See also " Inspection of Cotton Waste for Use in the Manufacture of Gun-cotton, by C. E. Munroe, J. Am. Chem. Soc.^ 1895, 1.7, 783.
METHODS OF DRYING THE COTTON.
79
<\J1
possible before dipping in the acids, especially if a wholly J " insoluble " nitro-cellulose is to be obtained. After dry- ing it should not contain more than 0.5 per cent, of moisture, and less than this if possible. The more general method of drying the cotton is in steam-jacketed tubes, i.e., double cylinders of iron, some 5 feet long and \\ feet wide. The cotton is placed in the central chamber (Fig. 12), while steam is made to circulate in the surrounding jacket, and keeps the whole cylin- der at a high temperature (steam pipes may be coiled round the outside of an iron tube, and will answer equally well). By means of a pipe which communicates with a compressed air reservoir, a current of air enters at the bottom,
and finds its way up through the cotton, and helps to remove the moisture that it contains. The raw cotton generally contains about 10 per cent, of moisture, and should be dried until it contains only J per cent, or less. For this it will generally have to remain in the drying cylinder for about five hours. At the end of that time a sample should be taken from the top of the cylinder, and dried in the water oven (100° C.*) for an hour to an hour and a half, and reweighed, and the moisture then remaining in it calculated.
It is very convenient to have a large copper water oven, containing a lot of small separate compartments, large enough to hold about a handful of the cotton, and
* It is dried at 180° C. at Waltham Abbey, in a specially con- structed drying chamber,
FIG. 12. — COTTON DRYER.
80 NITRO-EXPLOSIVES.
each compartment numbered, and corresponding to one of the drying cylinders. The whole apparatus should be fixed against the wall of the laboratory, and may be heated by bringing a small steam pipe from the boiler house. It is useful to have a series of copper trays, about 3 inches by 6 inches, numbered to correspond to the divisions in the steam oven, and exactly fitting them. These trays can then be taken by a boy to the drying cylinders, and a handful of the cotton from each placed in them, and afterwards brought to the laboratory and weighed (a boy can do this very well), placed in their respective divisions of the oven, and left for one to one and a half hours, and reweighed.
When the cotton is found to be dry the bottom of the drying cylinder is removed, and the cotton pushed out from the top by means of a piece of flat wood fixed on a broom-handle. It is then packed away in galvanised-iron air-tight cases, and is ready for the next operation. At some works the cotton is dried upon shelves in a drying house through which hot air cir- culates, the shelves being of canvas or of brass wire netting. The hot air must pass under the shelves and through the cotton, or the process will be a very slow one.
Dipping and Steeping. — The dry cotton has now to be nitrated. This is done by dipping it into a mixture of nitric and sulphuric acids. The acids used must be strong, that is, the nitric acid must be at least of a gravity of 1.53 to 1.52, and should contain as little nitric oxide as possible. The sulphuric acid must have a specific gravity of 1.84 at 15° C, and contain about 97 per cent, of the mono-hydrate (H2SO4). In fact, the strongest acids obtainable should be used when the product required is gun-cotton, /.£., the highest nitrate.
DIPPING AND STEEPING THE COTTON.
Si
The sulphuric acid takes no part in the chemical re- action involved, but is necessary in order to combine with the water that is liberated in the reaction, and thus to maintain the strength of the nitric acid. The reaction which takes place is the following : —
378
Cellulose.
594
1 08
Gun-Cotton.
Theoretically,* therefore, I part of cellulose should form 1.8 parts of gun-cotton. Practically, however, this is never obtained, and 1.6 Ibs. from I Ib. of cellulose is very good working. The mixture of acids used is generally I to 3, or 25 per cent, nitric acid to 75 per cent, sulphuric acid.
The dipping is done in cast-iron tanks (Fig. 13), a series of which is arranged in a row, and cooled by a stream of cold water flowing round them. The tanks hold about 12 gallons, and the cotton is dipped in por- tions of I Ib. at a time. It is thrown into the acids, and
FIG. 13.— TANK FOR DIPPING COTTON.
the workman moves it about for about three minutes with an iron rabble. At the end of that time he lifts it up on to an iron grating, just above the acids, fixed
OF THE
•0NIVERSI-J
OF
82
NITRO-EXPLOSIVES.
at the back of the tank, where by means of a movable lever he gently squeezes it, until it contains about ten times its weight of acids (the I Ib. weighs 10 Ibs.). It is then transferred to earthenware pots to steep.
The above-described process is in use in nearly all the gun-cotton works in England, but on the Continent other processes have been devised. Messrs Selwig & Lange, of Brunswick, for instance, have introduced what they term "a centrifugal nitrating apparatus," which consists of a perforated revolving basket in a centrifugal machine, which is arranged inside the acid
FIG. 14 — HYDRO-EXTRACTOR.
tank. The cotton, straw, &c., is nitrated within the machine, and after the acids are run off, the nitro- cellulose can be dried by centrifugal force. The ad- vantages of these nitrating machines do not appear to be very great, and it is doubtful if as uniform a nitration is obtained as dipping the cotton in small portions at a time.
Steeping. — The nitrated cotton, when withdrawn
S-TEEPING AND WASHING, ETC. 83
from the dipping tanks, and still containing an excess of acids, is put into earthenware pots of the shape shown in Fig. 15. The lid is put on, and the pots placed in rows in a wooden tank, about a foot deep, through which a stream of water is constantly flowing. This tank forms the floor of the steep- ing house. The cotton remains in these pots for a period of forty-eight hours, and must be kept cool. Between 18° and 19° C. is the highest temperature FIG _COTTON desirable, but the cooler the pots are kept STEEPING POT. the better. At the end of forty-eight hours the chemical reaction is complete, and the cotton is or should be wholly converted into nitro-cellulose ; that is, there should be no unnitrated cotton.
Whirling Out the Acid. — The next operation is to remove the excess of acid. This is done by placing the contents of two or three or more pots into a centrifugal hydro-extractor (Fig. 14), making 1,000 to 1,500 revolu- tions per minute. The hydro-extractor consists of a machine with both an inner cylinder and an outer one, both revolving in concert and driving outwardly the liquid to the chamber, from which it runs away by a discharge pipe. The wet cotton is placed around the inner cone. The cotton, when dry, is removed, and at once thrown into a large tank of water, and the waste acids are -collected in a tank.*
* Care must be taken in hot weather that the gun-cotton does not fire, as it does sometimes, directly the workman goes to remove it after the machine is stopped. It also occurs more often in damp weather. Dr Schiipphaus, of Brooklyn, U.S.A., proposes to treat the waste acids from the nitration of cellulose by adding to them sulphuric anhydride and nitric acid. The sulphuric anhydride added converts the water liberated from the cellulose into sulphuric acid.
84 NITRO-EXPLOSIVES.
Washing". — The cotton has now to be carefully washed. This is done in a large wooden tank filled with water. If, however, a river or canal runs through the works, a series of wooden tanks, the sides and bottoms of which are pierced with holes, so as to allow of the free cir- culation of water, should be sunk into a wooden platform that overhangs the surface of the river in such a way that the tanks are immersed in the water, and of course always full. During the time that the cotton is in the water a workman turns it over constantly with a wooden paddle. A stream of water, in the form of a cascade, should be allowed to fall into these tanks. The cotton may then be thrown on to this stream of water, which, falling some height, at once carries the cotton beneath the surface of the water. This proceeding is necessary because the cotton still retains a large excess of strong acids, and when mixed with water gives rise to considerable heat, especially if mixed slowly with water. After the cotton has been well washed, it is again wrung out in a centri- fugal machine, and afterwards allowed to steep in water for some time.
Boiling. — The washed cotton is put into large iron boilers with plenty of water, and boiled for some time at 1 00° C. In some works lead-lined tanks are used, into which a steam pipe is led. The soluble impurities of unstable character, to which Sir F. A. Abel traced the liability of gun-cotton to instability, are thereby removed. These impurities consist of the products formed by the action of nitric acid on the fatty and resinous substances contained in the cotton fibres. The water in the tanks should be every now and again renewed, and after the first few boilings the waters should be tested with litmus paper until they are no longer found to be acid.
PURIFYING AND PULPING THE GUN-COTTON. 85
Pulping. — The idea of pulping is also due to Abel. By its means a very much more uniform material is obtained. The process is carried out in an apparatus known as a "Beater" or "Hollander" (Fig. 16). It
FIG. i6«.— THE BEATER FOR GuN-Cora-ON.
consists of a kind of wooden tank some 2 or 3 feet deep of an oblong shape, in which a wheel carrying a series of knives is made to revolve, the floor of the tank being sloped up so as to almost touch the re- volving wheels. This part of the floor, known as the "craw," is a solid piece of oak, and a box of knives is fixed into it, against which the knives in the revolving wheel are
FIG. 16^.— WHEEL OF BEATEK.
86
NITRO-EXPLOSIVES.
pressed. The beater is divided into two parts — the wording side, in which the cotton is cut and torn between the knife edges in the revolving cylinder and those in the box ; and the running side, into which the cotton passes after passing under the cylinder. The wheel is generally boxed in to prevent the cotton from being thrown out during its revolution. The cotton is thus in constant motion, continually travelling round, and passing between the knives in the revolving cylinder and those in the box fixed in the wooden block beneath it. The beater is kept full of water, and the cotton is gradually reduced to a condition of pulp. The wheel • revolves at the rate of 100 to 150 times a minute.
When the gun-cotton is judged to be sufficiently fine, the contents of the beater are run into another very
FIG. ija. — POACHER FOR PULPING GUN-COTTON.
similar piece of machine, known as the " poacher " (Fig. 1 7, a, b, c\ in which the gun-cotton is continuously agitated together with a large quantity of water, which can be easily run off and replaced as often as required. When the material is first run into the poacher from the beater, the water with which it is then mixed is first run away and clean water added. The paddle wheel is then set in motion, and at intervals fresh water is added. There is a strainer at the bottom of the poacher which enables the water to be drawn off without disturbing the cotton pulp. After the gun-cotton has been in the poacher for
BEATERS AND POACHERS. 8/
some time, a sample should be taken by holding a rather large mesh sieve in the current for a minute or so. The pulp will thus partly pass through and partly be caught upon the sieve, and an average sample will be thus obtained. The sample is squeezed out by hand, bottled, and taken to the laboratory to be tested by the heat test
FIG 17^. — PLAN OF THE POACHER.
for purity. It first, however, requires to be dried. This is best done by placing the sample between coarse filter paper, and then putting it under a hand-screw press,
FIG. ijc.— ANOTHER FORM OF POACHER.
where it can be subjected to a tolerably severe pressure for about three minutest It is then rubbed up very finely with the hands, and placed upon a paper tray, about 6 inches by 4^ inches, which is then placed inside
88 NITRO-EXPLOSIVES.
a water oven upon a shelf of coarse wire gauze, the temperature of the oven being kept as near as possible to 120° F. (49° C.), the gauze shelves in the oven being kept about 3 inches apart. The sample is allowed to remain at rest for fifteen minutes in the oven, the door of which is left wide open. After the lapse of fifteen minutes the tray is removed and exposed to the air of the laboratory (away from acid fumes) for two hours, the sample being at some point within that time rubbed upon the tray with the hand, in order to reduce it to a fine and uniform state of division. Twenty grains (1.296 grms.) are used for the test. (See Heat Test, page 239.) If the gun-cotton sample removed from the poacher stands the heat test satisfactorily, the machine is stopped, and the water drained off. The cotton is allowed some little time to drain, and is then dug out by means of wooden spades, and is then ready for pressing. The poachers hold about 1,000 Ibs. of material, and as this represents the products of many hundred distinct nitrating operations, a very uniform mixture is obtained. Two per cent, of carbonate of soda is sometimes added, but it is not really necessary if the cotton has been properly washed.
Compressing Gun-Cotton. — The gun-cotton, in the state in which it is removed from the poacher, contains from 28 to 30 per cent, of water. In order to remove this, the cotton has to be compressed by hydraulic power. The dry compressed gun-cotton is packed in boxes con- taining 2,500 Ibs. of dry material. In order to ascertain how much of the wet cotton must be put into the press, it is necessary to determine the percentage of water. This may be done by drying 2,000 grains upon a paper tray (previously dried at 100° C.) in the water oven at
THE WALTHAM ABBEY PROCESS. 89
1 00° C. for three hours, and reweighing and calculating the percentage of water. It is then easy to calculate how much of the wet gun-cotton must be placed in the hopper of the press in order to obtain a block of compressed cotton of the required weight. Various forms of presses are used, and gun-cotton is sent out either as solid blocks, compressed discs, or in the form of an almost dry powder, in zinc-lined, air-tight cases. The discs are often soaked in water after compression until they have absorbed 25 per cent, of moisture.
The Waltham Abbey Process.— At the Royal Gun- powder Factory, Waltham Abbey, the manufacture of gun-cotton has been carried out for many years under the direction of Sir Frederick A. Abel. The process used differs but little from that used at Stowmarket. The cotton used is of a good quality, it is sorted and picked over to remove foreign matters, &c., and is then cut up by a kind of guillotine into 2-inch lengths. It is then dried in the following manner. The cotton is placed upon an endless band, which conducts it to the stove, or drying closet, a chamber heated by means of hot air and steam traps to about 180° F. ; it falls upon a second endless band, placed below the first ; it travels back again the whole length of the stove, and so on until delivered into a receptacle at the bottom of the 'farther end, where it is kept dry until required for use. The speed at which the cotton travels is 6 feet per minute,and as the length of the band travelled amounts to 1 26 feet, the operation of drying takes twenty-one minutes. One and a quarter Ibs. are weighed out and placed in a tin box ; a truck, fitted to receive a number of these boxes, carries it along a tramway to a cool room, where it is allowed to cool.
Dipping. — Mixed acids are used in the proportion
9O NITRO-EXPLOSIVES.
of I to 3, specific gravity nitric acid 1.52, and sulphuric acid 1.84. The dipping tank is made of cast iron, and holds 220 Ibs. of mixed acids, and is surrounded on three sides by a water space in order to keep it cool. The mixed acids are stored in iron tanks behind the dipping tanks, and are allowed to cool before use. During the nitration, the temperature of the mixed acids is kept at 70° F., and the cotton is dipped in quantities of i-| Ibs. at a time. It is put into a tin shoot at the back of the dipping tank, and raked into the acids by means of a rabble. It remains in the acids for five or six minutes, and is then removed to a grating at the back, pressed and removed. After each charge of cotton is removed from the tank, about 14 Ibs. of fresh mixed acids are added, to replace amount removed by charge. The charge now weighs, with the acids retained by it, 1 5 Ibs. ; it is now placed in the pots, and left to steep for at least twenty-four hours, the temperature being kept as low as possible, to prevent the formation of soluble cotton, and also prevent firing. The proportion of soluble formed is likely to be higher in hot weather than cold. The pots must be covered to prevent the absorption of moisture from the air, or the accidental entrance of water, which would cause decom- position, and consequent fuming off, through the heat generated by the action of the water upon the strong acids.
The excess of acids is now extracted by means of hydro-extractors, as at Stowmarket. They are worked at 1,200 revolutions per minute, and whirled for five minutes (loj Ibs. of waste acids are removed from each charge dipped). The charge is then washed in a very similar manner to that previously described, and again wrung out in a centrifugal extractor (1,200 revolutions per minute). The gun-cotton is now boiled by means of
MOULDING AND COMPRESSING GUN-COTTON. 91
steam in wooden tanks for eight hours ; it is then again wrung out in the extractors for three minutes, boiled for eight hours more, and again wrung out ; it is then sent to the beater and afterwards to the poacher. The poachers hold 1,500 gals, each, or 18 cwt. of cotton. The cotton remains six hours in the poachers. Before moulding, 500 gals, of water are run into the poacher, and 500 gals, of lime water containing 9 Ibs. of whiting and 9 gals, of a caustic soda solution. This mixture is of such a strength that it is calculated to leave in the finished gun-cotton from I to 2 per cent, of alkaline matter.
The pulp is now drawn off and up into the stuff chest by means of vacuum pressure. This chest is a large cylindrical iron tank, sufficiently elevated on iron standards to allow room for the small gauge tanks and moulding apparatus below. It holds the contents of one poacher (18 cwt), and is provided with revolving arms to keep the pulp stirred up, so that it may be uniformly suspended in water.
Moulding1. — By means of the small measuring tank above referred to, the gun-cotton pulp is drawn off from the stuff chest, and run into moulds of the shapes and sizes required. Thence a large proportion of the water is drawn off by means of tubes Connected with the vacuum engine, the moulds having bottoms of fine wire gauze, in order to prevent the pulp from passing through. Hydraulic pressure of about 34 Ibs. on the square inch is then applied, which has the effect of compressing the pulp into a state in which it has sufficient consistency to enable it to be handled with care, and also expels a portion of the remaining water.
Compressing. — The moulded gun-cotton is now
92 NITRO-EXPLOSIVES.
taken to the press house, which is situated at some dis- tance from the rest of the factory. Here the moulds are subjected to powerful hydraulic pressure, from 5 to 6 tons per square inch, and is compressed to one-third of its previous bulk. The slabs or discs thus formed are kept under pressure for a short time, not exceeding a minute and a half, to give the requisite density. It should, when removed, be compact, and just sink in water, and should perceptibly yield to the pressure of the ringers. There are perforations in the press blocks, to allow of the escape of gases, if formed, by reason of suffi- cient heat being generated. The men working the press are placed under cover, behind strong rope mantlets having eye tubes which command a view of the press.
Packing. — The finished slabs and discs are dipped into a solution of soda and carbolic acid, and packed in special wood metal-lined cases. When it is to be sent abroad, the metal lining, which is made of tinned copper, is soldered down, but both the outer wooden case and inner metal one are fitted with air-tight screw-plugs, in order that when necessary water can be added without unfastening the cases.
Reworked gun-cotton does not make such good discs as new pulped gun-cotton, probably because the fibrous tenacity of the gun-cotton has been destroyed by the amount of pressure it has previously undergone, so that when repulped it resembles fine dust, and a long time is required to press it into any prescribed form. It is generally boiled for eight hours to open up the fibre and remove alkali, then broken up by hand with wooden mallets, pulped, and then used with fresh gun-cotton in the proportion of I to 5 parts.
THE LE BOUCHET PROCESS. 93
Manufacture at Le Bouchet. — At Le Bouchet gun- cotton was made thus : 200 grms. of cotton were steeped for an hour in 2 litres of a mixture of I volume con- centrated nitric and 2 volumes sulphuric acid. The cotton was then removed and pressed, whereby y^ths of the waste acids was recovered. After this it was washed for one to one and a half hours in running water, strongly pressed again ; allowed to lie for twenty-four hours in wood-ash lye ; then well washed in running water ; pressed, and finally dried on a wide linen sheet, through which was forced air heated to 60° C. The average yield from 100 parts of cotton was 165 parts of gun-cotton. The strong pressings of the gun-cotton, while still impregnated with acids, caused subsequent washings to be difficult and laborious.
Granulation of Gun-Cotton. — Gun-cotton is often required in the granulated form for use either alone or with some form of smokeless powder. This is done under the patent of Sir Frederick Abel in the following manner : — The gun-cotton from the poacher is placed in a centrifugal machine, very similar to the hydro-extractors before mentioned, and used for wringing out the acids. In this machine it loses water until it only contains 33 per cent., and is at the same time reduced to a more or less fibrous state. It is then taken to the granulating room, where it is first passed through sieves or perfora- tions, which break up the mass into little pieces like shot. The material is then transferred to a revolving drum made of wood or stout leather, which is kept con- stantly revolving for some time. The material is occa- sionally sprinkled with water. The drum in turning, of course, carries the granules partially round with it, but the action of gravity causes them to descend constantly
94 NITRO-EXPLOSIVES.
to the lowest point, and thus to roll over one another continually. The speed of the drum must not be too rapid. None of the granules must be carried round by centrifugal force, but it must be fast enough to carry them some little distance up the side of the drum. After removal from the drum the granules are dried upon shelves in the drying house.
Gun-cotton is also dissolved in acetone or acetic acid until it has taken the form of a jelly. It is then rolled into thin sheets, and when dry cut up into little squares. In the manufacture of smokeless powders from nitro- cellulose, nitro-lignine, &c., the various substances are mixed with the gun-cotton or collodion-cotton before granulating.
Collodion-Cotton. — In the manufacture of collodion or soluble cotton the finer qualities of cotton waste are used, and the acids used in the dipping tanks are much weaker. The manufacture of collodion-cotton has become /of more importance than gun-cotton, by reason of its use / for the manufacture of the various forms of gelatine, such / as gelatine dynamite, gelignite, forcite, &c., and also on I account of its extensive use in the manufacture of many I of the smokeless powders. It is also used for the manu- facture of " collodion," which is a solution of collodion- cotton in ether-alcohol ; for the preparation of celluloid, and many other purposes. It is less explosive than gun- cotton, and consists of the lower nitrates of cellulose. It is soluble in nitro-glycerine, and in a mixture of 2 parts of ether and I of alcohol ; also in acetone, acetic ether, and other solvents. MM. Menard and Domonte were the first to prepare a soluble gun-cotton, and its investigation was carried on by Bechamp, who showed that its properties and composition were different to those of gun-cotton.
RSIT MANUFACTURE OF COLLODION-COTTON. 95
Manufacture. — The cotton used is cotton waste.* It is thought by some that Egyptian cotton is preferable, and especially long fibre varieties. The strength of the acids used is, however, of more importance than the quality of the cotton. The percentage composition of the acid mixture which gives the best results is as follows : — Nitric acid, 23 per cent. ; sulphuric acid, 66 per cent. ; and water, u per cent; and has a specific gravity of 1.712 (about). It can be made by mixing sulphuric acid of specific gravity 1.84 with nitric acid of specific gravity 1.368 in the proportions of 66 per cent, and 34 per cent, respectively. (The production of the penta-nitro-cellulose is "aimed at if the collodion-cotton is for use as an ex- plosive.) If the acids are much weaker than this, or potassium nitrate and sulphuric acid is used, the lower nitrates will be formed. The product, while being entirely soluble in ether-alcohol or nitro-glycerine, will have a low nitrogen content, whereas a material with as high a nitrogen as 12 or 12.6 is to be aimed at.
The cotton should not be allowed to remain in the dipping tanks for more than five minutes, and the acid mixture should be kept at a temperature of 65° C. or thereabouts ; and the cotton should be removed after a few minutes, and should not be pressed out, as in the case of gun-cotton, but at once transferred to the pots and allowed to steep for forty-eight hours. (Some prefer twenty-four hours, but there is more chance in this case of the product containing non-nitrated cellulose.) When the nitration is complete, the collodion-cotton is removed from the pots, and treated in exactly the same manner as described under gun-cotton. The produce should be entirely soluble in ether-alcohol and nitro-glycerine, and
* Raw cotton is often used.
96 NITRO-EXPLOSIVES.
contain as near 12.7 per cent, of nitrogen as possible. The theoretical nitrogen is for the penta-nitro-cellulose 12.75 Per cent. This will, however, seldom if ever be obtained. The following are some of the results I have obtained from different samples —
(i.) (2.) (3-)
German make 11.64 11.48 1 1.49 per cent.
Stowmarket 12.57 12.60 11.22 „
Walsrode - 11.61 12.07 Ir-99 »
Faversham 12.14 11.70 11.60 „
and the following was the analysis of a sample (No. i) of German made collodion-cotton, which made very good blasting gelatine : —
Soluble cotton (collodion) QQ.I 18 p. cent. 1
Gun-cotton 0.642 „ } Nitrogen- 1 ..64 p. cent.
Non-nitrated cotton - 0.240 „ Total ash - 0.25 „
It should contain as little non-nitrated or unconverted cotton and as little gun-cotton as possible, as they are both insoluble in nitro-glycerol. The quality and com- position of any sample of collodion-cotton can be quickly inferred by determining the percentage of nitrogen by means of the nitrometer and the use of the solubility test* A high nitrogen content coupled with a high solubility is the end to be aimed at ; a high nitrogen with a low solubility shows the presence of gun-cotton and a low nitrogen, together with a low solubility, the presence of unnitrated cotton.
Mr T. R. France claims to have invented some im- provements in the manufacture of soluble nitro-cellulose. His object has been to produce an article as uniform as possible. His explanation of the imperfect action of the
* See Analysis of Explosives, p. 203.
NITRATED GUN-COTTON. 97
acids is that, however uniform the mixed acids may be in strength and proportions, and however carefully the operations of nitrating, &c., may be conducted, there are variable elements found in different samples of cotton. The cotton fibre has for its protection a glazed surface. It is tubular and cellular in structure, and contains a natural semi-fluid substance composed of oil or gum, which varies in nature according to the nature of the soil upon which the cotton is grown. The tubes of the fibre seem to be open at one end only when the fibre is of normal length. When, therefore, the cotton is subjected to the action of the mixed acids, the line of least resist- ance seems to be taken by them, viz., the insides of the tubes, constituting the fibre of the cotton into which they are taken by capillary attraction, and are subject to change as they progress, and to the increased resistance from the oil or gum, &c., in their progress, and therefore to modified action, the result of which is slower and slower action, or chemical change. He also thinks it is possible that the power of capillary attraction is balanced in the tubes by air contained therein, after a little, suffi- ciently so to prevent the acids from taking full effect. To get over this, Mr France uses his cotton in a fine state, almost dust, in fact, and then nitrates in the usual mixture of acids at 40° to 90° F., the excess of acids being removed by pressure. He says he does not find it neces- sary to wash this fine cotton dust in an alkaline solution previous to nitration. His mixed acids consist of 8 parts HNO3 = 42° B, and 12 parts H2SO4 = 66° B., and he stirs in the dipping tank for fifteen minutes, the temperature being 50° F. to 100° F., the temperature preferred being 75° F.
Nitrated Gun-Cotton. — The nitrates that are or
G
98 NITRO-EXPLOSIVES.
have been mixed with gun-cotton in order to supply oxygen are potassium nitrate, ammonium nitrate, and barium nitrate (tonite). The total combustion of gun- cotton by potassium nitrate corresponds to the equa- tion : —
or 828 grms. of nitrate for 1,143 gnus. of gun-cotton, or 42 per cent, nitrate and 58 per cent, gun-cotton. The explosive made at Faversham by the Cotton Powder Company, and known as tonite No. i, consists of very nearly half gun-cotton and half barium nitrate. The relations by weight of total combustion would be 5.1.6 of gun-cotton to 48.4 of barium nitrate. The average com- position of tonite I have found by analysis to be 51.0 per cent, gun-cotton to 49.0 per cent, barium nitrate. The heat liberated is practically the same as for an equivalent weight of KNO3 ; but the barium nitrate mixture weighs 2,223 grms. instead of 1,971 grms., or one-eighth more. The advantage in mixing a nitrate with gun-cotton is that it supplies oxygen, and by con- verting all the carbon into carbonic acid, prevents the formation of the poisonous gas carbonic oxide (CO).
The Manufacture of Tonite. - - The explosive tonite was patented by Messrs Trench, Faure, and Mackie, and is manufactured at Faversham and Melling at the works of the Cotton Powder Company, and at San Francisco by the Tonite Powder Company. It consists of finely divided and macerated gun-cotton incorporated with finely ground nitrate of barium which has been carefully recrystallised. It is made by acting upon carbonate of barium * with nitric acid. The wet
* Witherite (BaCO:,)BaCO34-2HNO,-Ba(NO.,),
TONITE MANUFACTURE AND PROPERTIES. 99
and perfectly purified, finely pulped gun-cotton is intimately mixed up between edge runners with about the same weight of nitrate, and the mixing and grinding continued until the whole has become an intimately mixed paste. This paste is then compressed into cartridges, formed with a recess at one end for the pur- pose of inserting the detonator. The whole is then covered with paraffined paper.
The tonite No. 2 consisted of gun-cotton, nitrates of potash and soda, charcoal and sulphur. Tonite No. 3* is composed as follows : — Gun-cotton, 19 per cent. ; di-nitro-benzol, 13 per cent. ; and barium nitrate, 68 per cent, or similar proportions. It is a yellowish colour, and being slower in its explosive action, is better adapted for blasting soft rock.
Tonite is extensively used in torpedoes and for sub-/ marine blasting, also for quarries, &c. Large quantities/ were used in the construction of the Manchester Ship Canal. Among its advantages are, that the English railways will take tonite on the same footing as gun- powder ; it is a very dense material ; if wetted it can easily be dried in the sun ; it very readily explodes by the use of a proper detonator ; while it burns very slowly and without the least danger ; the cartridges being water- proofed, it can be employed in wet bore "holes, and it can j be tamped with water ; and finally, as it contains sufficient oxygen to oxidise the carbon, no carbonic oxide (CO)j gas is formed, t.e.t its detonation is perfect. It is a very, safe explosive to use, being little susceptible to eitheri blows or friction.
Quite lately a committee, composed of Prof. P.
* Tonite No. i was patented by Messrs Trench, Faure, and Mackie, and tonite Nos. 2 and 3 by Trench alone.
IOO NITRO-EXPLOSIVES.
Bedson, Drs Drummond and Hume, Mr T. Bell, one of H.M. Inspectors of Coal Mines, and others, in considering the problem whether the fumes produced by the com- bustion of tonite were injurious to health, carried out a series of experiments in coal mines for this purpose. The air at the " intake " was analysed, also the air of the " return," and the smoky air in the vicinity of the shot holes. The cartridge was surrounded by the flame- extinguishing mixture, and packed in a brown paper bag. During the first experiment nineteen shots were fired ( = 6.29 Ibs. tonite). The "return" air showed only a trace of carbonic oxide gas (CO). At the second experi- ment thirteen shots were fired ( = 4.40 Ibs. tonite), and analysis of the air of the " return " showed that CO was present in traces only, whilst the fumes contained only 1.9 to 4.8 parts per 10,000.
Dangers in connection with the Manufacture of Gun-cotton, &c. — Of all the nitro compounds, the least dangerous to manufacture are gun-cotton and collodion- cotton. The fact that the Stowmarket Factory is within five minutes' walk of the town shows how safe the manu- facture of this explosive is regarded. With the exception of the nitration and the compression into blocks or discs, the whole process is worked with a large excess of water, and the probability of an explosion is thus reduced to a minimum. Among the precautions that should, however, be taken, are — first, the careful extraction of the resinous and soluble substances from the cotton before nitration, as it was shown many years ago by Sir F. A. Abel that the instability of the gun-cotton first manufactured in England and Austria was chiefly due to these com- pounds. They are generally removed by boiling the cotton in a soda solution.
DANGERS IN CONNECTION WITH GUN-COTTON. IOI
The actual nitration of cotton is not a dangerous operation, but the operations of wringing in the hydro- extractors, and washing the nitro-cotton after it leaves the first centrifugal machine, are somewhat so. Great care should be taken that the wrung out nitro-cotton at once comes in contact with a large excess of water, i.e., is at once immersed entirely in the water, since at this stage it is especially liable to decomposition, which, once started, is very difficult to stop. The warmer the mixture and the less water it contains, the more liable it is to decomposition ; hence it is that on warm and damp days the centrifugal machines are most likely to fire. The commencement of decomposition may be at once detected by the evolution of red fumes. Directly the gun-cotton is immersed in the large quantity of water in the beater and poacher it is safe.
In order that the final product may be stable and have good keeping qualities, it is necessary that it should be washed completely fregjrnm arid The treatment in the beater and poacher, by causing the material to assume the state of a fine pulp, in contact with a large quantity of water, does a good deal to get rid of the free acid, but the boiling process is absolutely necessary. It has been proposed to neutralise the free acid with a dilute solution of ammonia ; and Dr G. O. Weber has published some experiments bearing upon this treat- ment. He found that after treatment with ammonia, the pyroxyline assumed a slightly yellowish tinge, which was a sure sign of alkalinity. It was then removed from the water, and roughly dried between folds of filter paper, and afterwards dried in an oven at 70° C. After three hours, however, an explosion took place, which entirely destroyed the strong copper oven in which the nitro- cotton (about I oz.) had been drying. The explosion
102 NITRO-EXPLOSIVES.
was in some respects remarkable. The pyroxyline was the di-nitro-cellulose (or possibly the penta-nitro ?), and the temperature was below the igniting point of this material (40° C. would have been a better temperature). Dr Weber determined the ignition point of his di-nitro- cellulose, and found it to be 194° to 198° C., and he is therefore of opinion that the explosion was due to the treatment of the partially washed material with ammonia. A certain quantity of ammonium nitrate was probably formed, and subsequently dried upon the nitro-cellulose, in a state of very fine subdivision. The faintest trace of acid would then be sufficient to bring about the explosive ignition of the ammonium nitrate, v The drying of gun-cotton or collodion-cotton is also /a somewhat dangerous operation. A temperature of | 40° C. (104° F.) should not be exceeded, and thermometers should be placed in the nitro-cotton, and the temperature frequently observed. An electric alarm thermometer is also a useful adjunct to the cotton drying house. Great care must also be taken that there are no exposed hot- water pipes or stoves in the drying house, as the fine gun- cotton dust produced by the turning or moving of the material upon the shelves would settle upon such pipes or stoves, and becoming hot, would be very sensitive to the least friction. The floor also should be covered with linoleum or indiarubber. When hot currents of air are made to pass over the surface of gun-cotton, the gun- cotton becomes electrified. It is important, therefore, to provide some means to carry it away. Mr W. F. Reid, F.I.C., was the first to use metal frames, carriers, and sieves, upon which is secured the cloth holding the gun- cotton, and to earth them.
The compression of gun-cotton into blocks, discs, &c., is also attended with considerable risk. Mr O. Guttmann,
DANGERS IN CONNECTION WITH GUN-COTTON. 103
in an interesting paper upon "The Dangers in the Manu- facture of Explosives" (Jour. Soc. C/iem. hid., No. 3, vol. xi., 1892), says: "The compression of gun-cotton into cartridges requires far more care than that of. gun- powder, as this is done in a warm state, and gun-cotton even when cold, is more sensitive than gunpowder. When coming out of the centrifugal machines, the gun- cotton should always pass first through a sieve, in order to detect nails or matches which may by chance have got into it. What has been said as to gunpowder presses applies still more to those for gun-cotton, although the latter are always hydraulic presses. Generally the pistons fit the mould perfectly, that is to say, they make aspira- tion like the piston of a pump. But there is no metal as yet known which for any length of time will stand the constant friction of compression, and after some time the mould will be wider in that part where the greatest com- pression takes place. The best metal for this purpose has proved to be a special steel made by Krupp, but this also is only relatively better ; for pistons I prefer hard cast iron. If the position of the moulds and pistons is not exactly the same in all cases, what the Germans call ' Ecken ' (English ' binding ') will take place, viz., the mould will stand obliquely to the piston, and a dangerous friction will result.'' " Of course, it is necessary to protect the man working the hydraulic valves during compression. At Waltham Abbey they have a curtain made of ship's hawsers, which is at the same time elastic and resistant." Mr Guttmann has found that a partition wall 12 inches thick, made of 2-inch planks, and filled with ground cinders, gives very effective protection. A door in this partition enables the workman to get to the press, and a conical tube penetrates the wall, enabling the man to see the whole work from a safe standpoint. The roof, or
IO4 NITRO-EXPLOSIVES.
one side of the building, should* be of glass, so as to give the explosion a direction.
Trench's Fire-extinguishing Compound is manu- factured by the Cotton Powder Company at Faversham, and is the invention of Mr George Trench, F.C.S., the manager of the Company. The object of the invention is to surround the cartridges of tonite, when used in coal mines, with a fire-extinguishing compound. If a charge of tonite, dynamite, or gelatine dynamite is put inside a few ounces of this mixture, and then fired, not the least trace of flame can be observed, and experiments appear
FIG. 18.— TRENCH'S FIRE-EXTINGUISHING CARTRIDGE.
to show that there is no flame at all. The compound consists of sawdust impregnated with a mixture of alum and chlorides of sodium and ammonia. Fig. 18 shows the manner of placing the tonite cartridge in the paper bag, and surrounding it with the fire-extinguishing com- pound, a a. The attachment of the fuse and detonator is also shown.
The following report (taken from the Faversham News, 22nd Oct. 1887) of experiments conducted in the presence of several scientific and mining men will show its value : — " A large wrought-iron tank, of 45 cubic feet capacity, had been sunk level with the ground in the middle of the yard ; to this tank the gas had been laid on, for a purpose that will be explained later on. The
TRENCH'S FIRE-EXTINGUISHING COMPOUND. 105
charges were fired by means of electricity, a small dynamo-firing machine being placed from 30 to 40 yards away from the * mine.' " Operations were commenced by the top of the tank being covered over and plastered down in order to make it air tight ; then a sufficient quantity of coal gas was placed in it to make it highly inflammable and explosive, the quantity being ascer- tained by a meter which had been fixed specially for the purpose. Whilst the gas was being injected the cartridge was prepared.
The first experiment was to try whether a small charge of tonite — fired without the patent extinguisher — would ignite the gas. The gas having been turned on, a miner's lamp was placed in the " tank," but this was extinguished before the full quantity of gas had gone through the meter. However, the gas being in, the charge of ij oz. tonite was placed in the "mine," the detonator was connected by means of long wires to the dynamo machine, and the word was given to " fire." With a tremendous report, and a flash of fire, the cover- ing of the mine flew in . all directions, clearly showing that the gas had exploded. The next cartridge (a similar charge) was prepared with the patent compound. First of all a brown paper case of about 2 inches diameter was taken, and one of the -tonite cartridges was placed in the centre of it, the intervening space between the charge and the case being packed with the " fire-extinguishing compound." The mine having had another supply of gas injected, the protected car- tridge was placed inside and fired. The result was astonishing, the explosion not being nearly so loud, whilst there was not the least flash of fire. " Protected " and " unprotected " charges were fired at intervals, gas being turned into the tank on each occasion. Charges
106 NITRO-EXPLOSIVES.
of tonite varying from I to 6 oz. were also used with the compound. The report was trifling, whilst no flash could be seen.
Uses of Collodion-Cotton. — The collodion or soluble gun-cotton is used for a variety of purposes. The chief use is, however, for the manufacture of the various explosive gelatine compounds, of which blasting gelatine is the type. It is also very extensively used in the manufacture of smokeless powders, both military and sporting — in fact, very few of them do not contain it. In some, how- ever, nitro-lignose or nitrated wood is used instead. This, however, is chemically the same thing, viz., nitro-cellulose, the cellulose being derived from the wood fibre. It is more used in this connection than the higher nitrate gun-cotton. Another use to which it has been applied very extensively, of recent years, is in the manufacture of " celluloid." It is used in photography for the prepara- tion of the films on the sensitised plates, and many other purposes. Dissolved in a solution of two parts ether and one of alcohol, it forms the solution known as collodion, used for a variety of purposes, such as a varnish, as a paint for signals ; in surgery, for uniting the edges of wounds.
Quite lately, Mr Alfred Nobel, the well - known inventor of dynamite, has patented the use of nitro- cellulose, hydro- or oxy-cellulose, as an artificial sub- stitute for indiarubber. For this purpose it is dissolved in a suitable non-volatile or slightly volatile "solvent," such as nitro-naphthalene, di-nitro-benzene, nitro-toluene, or its homologues ; products are obtained varying from a gelatinous consistency to the hardness of ebonite. The proportions will vary from about 20 per cent, of nitro- cellulose in the finished product, forming a soft rubber,
USES OF COLLODION-COTTON AND CELLULOID. 10?
to 50 per cent, nitrating celluloid, and the "solvent" chosen will depend on the use to which the rubber substitute is to be put, the liquids giving a more elastic substance, while mixtures of solids and liquids may be employed when the product is to be used at high tem- peratures. By means of rollers steam heated, the incor- poration may be accomplished without the aid of a volatile liquid, or the nitro-cellulose may be employed wet, the water being removed after " solution."
It is advisable to use the cellulose nitrated only just enough to render it suitable, in order to reduce the inflammability of the finished product. Mr W. Allen, M.P., of Gateshead, proposes' to use celluloid for car- tridge cases, and thus to lighten ammunition, and pre- vent jambing, for the case will be resolved into gases along with the powder. Extractors will also be done away with.
Celluloid is an intimate mechanical mixture of pyr- oxyline (gun-cotton or collodion-cotton) with camphor, first made by Hyatt, of Newark, U.S.A., and obtained by adding the pyroxyline to melted camphor, or by strongly compressing the two substances together, or by dissolv- ing the constituents in an appropriate solvent, e.g., alcohol or ether, and evaporating to dryness. ' A combination of the two latter methods, i.e., partial solution, with pressure, is now usually adapted. The pyroxyline employed is generally the tetra- and penta-nitrated cellulose, the hexa-nitrate (gun-cotton) being but seldom used on account of its explosive properties.
Care is taken to prevent the formation of the hexa- nitrate by immersing the cellulose in only moderately strong nitric acid, or in a warm mixture of nitric and sulphuric acids. Thin paper, either in small pieces or in
IO8 NITRO-EXPLOSIVES.
sheets, is immersed for about twenty-five minutes in a mixture of 2 parts of nitric acid and 5 parts of sulphuric acid, at a temperature of about 30° C, after which the nitrated cellulose is thoroughly washed with water to remove the last traces of free acid, pressed, and whilst still moist, mixed with the cam- phor.
In the process of Trebouillet and De Besancele, the cellulose, which may be in the form of paper, cotton, or linen, is twice nitrated — first in the acid mixture employed in a previous operation ; and secondly, in a fresh mixture of 3 parts sulphuric acid of 1.83 specific gravity, and 2 parts concentrated nitric acid containing nitrous acid. After each nitration the mass is subjected to pressure, and is then carefully washed with water, to which, at the last, a small quantity of ammonia or caustic soda is added to remove the final traces of acid. The impregnation of the pyroxyline with the camphor is effected in a variety of ways.
The usual proportion of the constituents is 2 parts pyroxyline and I part camphor. In Trebouillet and De Besancele's process, 100 parts of pyroxyline are intimately mixed with from 40 to 50 parts camphor, and moulded together by strong pressure in a hot press, and afterwards dried by exposure to air, desiccated by calcium chloride or sulphuric acid. The usual method is, however, to dissolve the camphor in the least possible quantity of alcohol, and sprinkle the solution over the dry pyroxyline, which is then covered with a second layer of pyroxyline, and the whole again treated with the camphor solution, the addition of pyroxyline and camphor solution being repeated alternately until the requisite amount of celluloid mixture is obtained.
The mass, which sinks together in transparent lumps,
CELLULOID.
is worked for about an hour between cold iron rollers, and then for the same period between rollers which can be gently heated by steam. The layer of celluloid surround- ing the rollers is then cut away and again pressed, the resulting cake, which is now about I cm. thick, being cut into plates of about 70 cm. long and 30 cm. broad. These are placed one above the other, and strongly pressed together by hydraulic pressure at a temperature of about 70° for twenty-four hours. The thick cakes are once more cut into plates of the desired thickness, and placed in a chamber heated from 30° to 40° for eight to fourteen days, whereby they become thoroughly dry, and are readily made into various articles either by being moulded while warm under pressure, cut, or turned. Occasionally other liquids, e.g., ether and wood spirit, are used in place of alcohol as solvents for the camphor.
Celluloid readily colours, and can be marbled for manufacturing purposes, Sac. It is highly inflammable and not explosive even under pressure, and may be worked under the hammer or between rollers without risk. It softens in boiling water, and may be moulded or pressed. Its specific gravity varies slightly with its composition and with the degree of pressure it has received. It is usually 1.35. It appears to be merely a mixture of its components, since by treatment with appropriate solvents the camphor may be readily ex- tracted, and on heating the pyroxyline burns away while the camphor volatilises.
The manufacture of pyroxyline for the purpose of making celluloid has very much increased during recent years, and with this increase of production improved methods of manufacture have been invented. A series of interesting papers upon the manufacture of pyroxyline has been published by Mr Walter D. Field, of New
I 10 NITRO-EXPLOSIVES.
York, in the Journal of the American Chemical Society* from which the following particulars are taken : —
Selection of the Fibre. — Cotton fibre, wood fibre, and flax fibre in the form of raw cotton, scoured cotton, paper, and rags are most generally used, and give the best results. As the fibres differ greatly in their structure, they require different methods of nitrating. The cotton fibre is a flattened hollow ribbon or collapsed cylindrical tube, twisted a number of times, and closed at one end to form a point. The central canal is large, and runs nearly to the apex of the fibre. Its side walls are mem- braneous, and are readily penetrated by the mixed acids, and consequently the highest nitration results. In the flax fibre the walls are comparatively thick, the central canal small ; hence it is to be presumed that the nitration must proceed more slowly than in the case of cotton. The New Zealand flax gives the most perfectly soluble nitrates of any of the flaxes. Cotton gives a glutinous collodion, and calico a fluid collodion. One of the largest manufacturers of pyroxyline in the States uses the " Memphis Star " brarid of cotton. This is an upland cotton, and its fibres are very soft, moist, and elastic. Its colour is light creamy white, and is retained after nitration. The staple is short, and the twist inferior to other grades, the straight, ribbon-like filaments being quite numerous. This cotton is used carded, but not scoured. This brand of cotton contains a large quantity of half and three-quarter ripe fibre, which is extremely thin and transparent, distributed throughout the bulk of the cotton (Monie., Cotton Fibre, 67). Mr Field says,
* Vol. xv., No. 3, 1893 ; Vol. xvi., No. 7, 1894 ; Vol. xvi., No. 8, 1894. Figs. 19, 20, 21, 22, and 23 are taken from Mr Field's paper.
MANUFACTURE OF CELLULOID. I I I
"This is a significant fact when it is known that from this cotton an extremely soluble pyroxyline can be produced."
Pyroxyline of an inferior grade as regards colour only can be produced from the cotton wastes of the trade. They must be scoured before they are fit for nitrating. Paper made from the pulps of sulphite and sulphate processes is capable of yielding a very soluble pyroxyline. It can be nitrated at high temperatures and still yield good results. Tissue paper made from flax fibre is also used after being cut into squares.
Mowbray (U.S.P., No. 443, 105, 3rd December 1890) says that a pure cotton tissue paper less than -^ inch in thickness, thin as it is, takes on a glutinous or colloid surface, and thus requires some thirty minutes to enable the nitration to take place. With a thicker paper only the surface would be nitrated. He therefore uses a fibre that has been saturated with a solution of nitrate of soda, and afterwards dried slowly, claim- ing that the salt crystallises in the fibre, or enters by the action termed osmose, and opens up the fibre to the action of the acid. This process would only be useful when the cotton is to be nitrated at a low tem- perature. At a high temperature it would be unnecessary.
Dietz and Wayne (U.S. P., No. 133, 969) use ramie, rheca, or China grass for producing a soluble pyroxyline. That made from ramie is always of uniform strength and solubility, and requires a smaller quantity of solvent to dissolve it than that made from cotton. Mr Field's experience, however, is entirely contrary to this state- ment. Such is the influence of the physical form of the fibre on the process of nitration, that when flax fibre and cotton fibre are nitrated with acid mixtures of exactly the same strength, and at the same temperature, the solution of the first is glutinous or thick, and the second
TtTO'T VET3fiTr
112 N1TRO-EXPLOSIVES.
fluid or thin. By simply nitrating at a higher tempera- ture than the cotton, the flax will yield a pyroxyline giving an equally fluid collodion.
The presence of chlorine in the fibre must be carefully avoided, as such a fibre will yield an acid product which cannot be washed neutral. The fibre must be dry before nitration ; and this is best done, according to Mr Field, by using the form of drier used in drying wool.
Nitration of the Fibre. — Mixed cotton and flax fibre in the form of paper, from TT^o to y^y inch thick, and cut into i -inch squares, is nitrated by the Celluloid Manufac- turing Company, and the same paper, left in long strips, I -inch wide, is used for nitration by the Xylonite Manu- facturing Company, of North Adams, Mass. (U.S.A.).
The Celluloid Company introduce the cut paper into the mixed acids by means of a hollow, rapidly revolving tube, flared at the lower end, and immersed in the mixed acids. The centrifugal force of the revolving tube throws the paper towards the sides of the vessel, leaving the centre of the vessel ready for fresh paper.
The Xylonite Company simply cut the paper into long strips, and introduce it into the mixed acids by means of forks. The arrangement used by this Com- pany for holding the mixed acids is a cylindrical vessel divided into a number of sections, the whole revolving like a turntable, thus allowing the workman to nitrate successively each lot of paper at a given point. This Company did not remove the acid from the paper after its immersion, but plunged it immediately into the water, thus losing a large proportion of the waste acid. The Celluloid Company, by using the paper in smaller pieces, and more paper to a pound of acid, and wringing the mixed acid from the paper before immersion in water, had a better process of nitration.
CELLULOID — THE APPARATUS USED.
113
FIG. 19. — VESSEL FOR NITRATING COTTON OR PAPER.
Other manufacturers use earthenware vessels, and glass or steel rods, hooked at one end, having small pieces of rubber hose pulled over the other end to pre- vent the hand from slipping. The form of vessel in general use is that given in Fig. 19. It is large enough to nitrate I Ib. of cotton at a time. The hook at one end of the rod enables the workman to pull the pyroxyline apart, and thus ensures saturation of the fibre. In the winter the room in which the nitrating is done must be kept at a temperature of about 70° F. in order to secure equality in the batches.
The nitrating apparatus of White and Schupphous (U.S.P., No. 418, 237, 89) Mr Field considers to be both novel and excellent. The cage (Fig. 21), with its central perforated cylinder (Fig. 20), is intended to ensure
B'
FIG. 20. — CENTRAL PERFORATED FIG. 21. — THE CAGE.
CYLINDER. WHITE AND SCHUPPHOUS' NITRATING APPARATUS.
the rapid and perfect saturation of the tissue paper used for nitrating. The patentees say that no stirring is required with their apparatus. This, says Mr Field, might be true when paper is used, or even cotton, when the temperature of nitration is from 30° to 35° C., but would not be true if the temperature were raised to 50°
H
NITROEXPLOSIVES.
to 55° C. The process is as follows: — The paper is nitrated in the cage (Fig. 20), the bottom of which is formed by the flanged plate C, fastened to the bottom of the internal cylinder B. After nitration the cage is
FIG. 22<i.— CELLULOID NITRATING POT.
FIG. 22^. — ANOTHER VIKW.
carried to a wringer, which forms the basket, and the acids removed. Finally, the cage is taken to a plunge tank, where the paper is removed from the cage by simply pulling out the central perforated cylinder B. Fig. 22 shows the nitrating pot, with its automatic
FIG. 23.— PLUNGE TANK.
cover. The plunge tank is shown in section and plan in Fig. 23. This apparatus is suitable for the nitration of cotton fibre in bulk at high or low temperatures. Other methods that have been patented are Mowbray's (U.S. P.,
ACID MIXTURE FOR MAKING CELLULOID. 115
No. 434, 287), in which it is proposed to nitrate paper in continuous lengths, and Hyatt's (U.S. P., No. 210, 611).
The Acid Mixture. — Various formulae have been published for producing soluble nitro -cellulose. In many instances, although the observations were correct for the single experiment, a dozen experiments would have produced a dozen different products. The com- position of the acids used depends upon the substance to be nitrated, and the temperature at which the nitration will be worked. Practically there are three formulae in general use — the one used by the celluloid manufac- turers ; another in which the cotton is nitrated at high temperatures ; and a third in which the temperature of the immersion is low, and the time of nitration about six hours. Of the three, the best method is the last one, or the one in which the cotton is immersed at a low tem- perature, and then the reaction allowed to proceed in pots holding from 5 to 10 Ibs. of cotton. The formula used by the celluloid manufacturers for the production of the low form of nitrated product which they use is : — Sulphuric acid - - - - 66 parts by weight.
Nitric acid 17 „ „
Water - - 17 „ „
Temperature of immersion, 30° C. Time, twenty to thirty minutes.
The cellulose is used in the form of tissue paper T<foo m°h thick, i Ib. to 100 of acid mixture. The nitro-cellulose produced by this formula is very insoluble in the compound ethers and other solvents of pyroxyline, and is seemingly only converted or gelatinised by the action of the solvent. The next formula produces a mix- ture of tetra- and penta-nitro-celluloses hardly soluble in methyl-alcohol (free from acetone), but very soluble in anhydrous compound ethers, ketones, and aldehydes: —
N ITRO-EXPLOSI VES.
Nitric acid, sp. gr. 1.435 - - - 8 Ibs.
Sulphuric acid, sp. gr. 1.83 - 15! „
Cotton - 14 oz.
Temperature of nitration, 60° C. Time of immersion, forty-five minutes.
The 60° of temperature is developed by mixing the acids together. The cotton is allowed to remain in the acid until it feels " short " to the rod.
The following table, due to Mr W. D. Field, shows very plainly the great variation in the time of the immer- sion and the temperature by seemingly very slight causes. It extends over fourteen working days, during which time it rained four days. The formula used is that given above, except that the specific gravity of the nitric acid is somewhat lower. The product obtained differs only from that produced by using nitric acid of specific gravity 1.43 in being soluble in methyl-alcohol. From 30 to 35 Ibs. of pyroxyline were produced in each of the fourteen days.
|
Specific Gravity. |
Time. |
Temp., Deg. C. |
3ercentage. |
|||||||
|
H2S04- |
HNO3. |
Hours. |
Minutes. |
S2 § K |
Minutes. |
i h |
£ |
Increase. |
4 S |
|
|
i Clear |
1.838 1.837 1.837 1.837 I.S377 1.8391 1.835 1.835 1.824 1.83 1.832 1.822 1.8378 1.837 |
.4249 .4249 .4226 .420 .42 .422 .4226 .422 .4271 .4271 .425 .425 •4257 .4257 |
I I |
20 20 45 20 15 35 20 35 20 IO 10 10 50 56 |
4 2 2 2 I I I I 4 |
2O 40 35 10 25 5o 20 40 40 |
57° 60° 60° 60° 58° 58° 62° 60° 50° 58° 58° 58° 50° 5o° |
62° 62° 62° 63; 62 62° 64° 62° 60° 60° 60° 60° 58° 60° |
It 7 o 15 5 "s 20 16 |
0 2 10 3 IO IO |
|
2. ,, 3. Cloudy 4. Rain 5. Clear 6. Rainy 7. Cloudy g Clear |
||||||||||
|
9. Partly clear 10. 11. Cloudy 12. Rainy 13. Partly clear 14. Cloudy |
FIELD ON CELLULOID MANUFACTURE. 117
A careful examination of this table will prove very instructive. The increase in yield varies from 31 per cent, to nothing, and the loss runs as high as 10 per cent, yet care was taken to make the product uniform in quality. On the days it rained there was a loss, with the exception of the fourth day, when there was neither a loss nor a gain. On the days it was partly clear, as just before or after rain, the table shows a loss in product. We can explain this fact by reason of the moisture- absorbing qualities of the cotton. On the rainy days it would absorb the moisture from the air until, when im- mersed in the acids, they were weakened, and the fibre dissolved more or less in weakened acid, producing what is known as " burning " in the batch. It will also be noticed that on days which show a loss, the time of the immersion was correspondingly short, as on the tenth, twelfth, and seventh days.
The lesson this table teaches is, that it is almost im- possible to nitrate cellulose in small quantities, and get uniform results, when the nitration is carried on at high temperatures. As regards the solubility of pyroxyline, Parks found that nitro-benzene, aniline, glacial acetic acid, and camphor, dissolved in the more volatile solvents methyl-alcohol and alcohol-ether, were much the best solvents for producing a plastic, as they are less volatile, and develop greater solvent action under the influence of heat. Nitro-benzene gives a solution that is granular ; it seems to merely convert the pyroxyline, and not to dissolve it ; but on the addition of alcohol, a solution is at once obtained, and the granular appearance disappears, and the solution becomes homogeneous. The acid mixture and the method of nitrating have much to do with the action of the various solvents, so also has the presence of water.
1 1 8 NITRO-EXPLOSIVES.
Dr Schupphous found that propyl and isobutyl alco- hols with camphor were active solvents, and the ketones, palmitone, and stearone in alcohol solution, also alpha and beta-naphthol, with alcohol and anthraquinone (dipheny- lene diketone) in alcoholic solution, and also iso-valeric aldehyde and its derivatives, amyliden-dimethyl and amyliden-diethyl ethers.
August Sayer (U.S. P., No. 470, 451) finds diethyl- ketone, dibutyl-ketone, di-pentyl-ketone, and the mixed ketones,* methyl-ethyl, methyl -propyl, methyl-butyl, methyl-amyl, and ethyl-butyl ketones are active solvents of pyroxyline ; and Paget finds that although methyl- amyl oxide is a solvent, that ethyl-amyl oxide is not.
The solvents of pyroxyline can be divided into general classes — First, those which are solvents without the aid of heat or solution in alcohol ; second, those that are solvents when dissolved in alcohol. These solvents are those which also develop a solvent action when heated to their melting point in combination with pyroxyline.
Mr W. D. Field groups the solvents of pyroxyline into classes thus : — Two of the monohydric alcohols ; compound ethers of the fatty acids with monohydric alcohols, aldehydes ; simple and mixed ketones of the fatty acid series. These four classes include the greater number of the solvents of pyroxyline. Those not included are as follows : — Amyl-nitrate and nitrite, methylene-di- methyl ether, ethidene-diethyl ether, amyl-chloracetate,
* Ketones are derived from the fatty acids by the substitution of the hydroxyl of the latter by a monad positive radical. They thus resemble aldehydes in constitution. The best-known ketone is acetone CH3.CO.CH3. Mixed ketones are obtained by dis- tilling together salts of two different fatty acids. Thus potassic butyrate and potassic acetate form propyl-methyl-ketone —
rc(c.2H5) ICO.CH,
CELLULOID. 119
nitro-benzene and di-nitro-benzene, coumarin, camphor, glacial acetic acid, and mono-, di-, and tri-acetin.
Richard Hale uses the following solvent : — Amyl- acetate, 4 volumes ; petroleum naphtha, 4 volumes ; methyl-alcohol, 2 volumes ; pyroxylin, 4 to 5 ounces to the gallon of solvent. Hale used petroleum naphtha to hasten the drying qualities of- the varnish, so that it would set on the article to be varnished before it had a chance to run off. It is, however, the non-hygroscopic character of the solvent that makes the varnish success- ful. This formula is very largely used for the production of pyroxyline varnish, which is used for varnishing pens, pencils, &c., also brass-work and silver-ware.
The body known as oxy-cellulose* is formed by the action of nitric acid upon cellulose when boiled with it. The quantity formed is about 30 per cent, of cellulose acted upon. When washed free from acid, it gelatinises. It is then soluble in dilute alkalies, and can be re- precipitated from solution by alcohol, acids, or saline solutions. Messrs Cross and Bevan assign to it the formula C18H26O16. It dissolves in concentrated sulphuric acid, and with nitric acid forms a nitro body of the formula C18H23O163(NO2), which is prepared as follows : —The gelatinous oxy-cellulose is washed with strong nitric acid until free from water, and is then diffused through a mixture of equal volumes of strong sulphuric and nitric acids, in which it quickly dissolves. The solu- tion, after standing for about an hour, is poured in a fine stream into a large volume of water, by which the " nitro " body is precipitated as