~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 1 to 5 parts.
~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 1 volume concentrated nitric and 2 volumes sulphuric acid. The cotton was then removed and pressed, whereby 7/10ths 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 perforations, 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 constantly revolving for some time. The material is occasionally 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 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 ether 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 account of its extensive use in the manufacture of many of the smokeless powders. It is also used for the manufacture 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 1 of alcohol; also in acetone, acetic ether, and other solvents. MM. Ménard and Domonte were the first to prepare a soluble gun- cotton, and its investigation was carried on by Béchamp, who showed that its properties and composition were different to those of gun-cotton.
~Manufacture.~—The cotton used is cotton-waste.[A] 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, 11 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 explosive.) 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.
[Footnote A: Raw cotton is often used.]
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 28° 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 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:—
Nitrogen.
(1.) (2.) (3.)
German make 11.64 11.48 11.49 per cent.
Stowmarket 12.57 12.60 11.22 "
Walsrode 11.61 12.07 11.99 "
Faversham 12.14 11.70 11.60 "
and the following was the analysis of a sample (No. 1) of German-made collodion-cotton, which made very good blasting gelatine:—