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 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 ascertained 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 1-1/4 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 covering 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 cartridge 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 of tonite varying from 1 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, however, 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 preparation 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 substitute 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, 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, whilst mixtures of solids and liquids may be employed when the product is to be used at high temperatures. By means of rollers steam heated, the incorporation 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, proposed to use celluloid for cartridge cases, and thus to lighten ammunition, and prevent 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 pyroxyline (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 dissolving 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. The paper, either in small pieces or in 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 camphor.
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 1 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, 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 surrounding the rollers is then cut away and again pressed, the resulting cake, which is now about 1 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.