756 GUN-COTTON 



1. The cleansing and perfect desiccation of tho cotton previously to its immersion 

 in the mixed acids. 



2. Tho employment of the strongest acids procurable in commerce. 



3. The steeping of tho cotton in a fresh strong mixture of acids after tho first 

 immersion and partial conversion into gun-cotton. 



4. The continuance of the steeping for forty-eight hours. 



5. The thorough purification of tho gun-cotton thus produced from every traco of 

 free acid, by washing tho product in a stream of water for several weeks ; subse- 

 quently a weak solution of potash may bo used, but this is not essential. 



The prolonged application of these processes is absolutely necessary to ensure tho 

 thorough nitration of the cotton, and the subsequent purification of the product ; for 

 each cotton fibre is a long narrow tube, often twisted and even doubled up, and tho 

 acid has first to penetrate to the inmost depths of these tubes and afterwards to be 

 soaked out of them ; henco tho necessity of time. 



Sometimes, to render the gun-cotton less spontaneously explosive, and to remove tho 

 last lingering traces of free acid, it is impregnated with a solution of silicate of soda 

 (soluble glass) which is forced into it by moans of a centrifugal machine, having a 

 central tube for supplying tho solution. It is then dried by exposure to the air, 

 whereby carbonate of soda is formed, and silica separated', and the carbonate of soda is 

 afterwards washed out with water while the silica remains attached to the fibres. 



Sometimes, again, to render the fibres soft, and diminish tho danger of explosion 

 from violent friction, the gun-cotton, after being treated with soluble glass, is im- 

 mersed in a soap-ley, the excess of which is then squeezed out, and the gun-cotton 

 finally dried. 



Gun-cotton was prepared on a largo scale by a process essentially the same as 

 that of Von Lenk, at the manufactory of Messrs. Prentice at Stowmarket, previous to 

 its destruction by fire. Preparations are now (1874) being made for resuming the 

 manufacture in this place. 



Gun-cotton prepared by Von Lenk's process is not liable to explosion by percussion ; 

 it may detonate between iron and iron if a heavy blow be struck, but only that part 

 explodes which is hit, without communicating ignition to the surrounding particles, 

 If a heavy blow be struck on gun-cotton with an iron hammer, upon bronze or any 

 other comparatively soft metal, no detonation takes place. Otto found, on the other 

 hand, that pyroxyline, prepared with nitric acid ^alone, explodes like fulminating 

 mercury when struck with a hammer. 



The temperature at which gun-cotton explodes has been very accurately determined 

 by Baron von Ebner, who fixes the lowest temperature at 136 C. (2770 Fahr.); but 

 the heat required is usually stated to be greater than this. According to Melsens, 

 gun-cotton which has been washed with soda and retains a small quantity of the 

 nlkali, does not explode till heated to 180 C., and similar observations have been 

 made by Payen, Pelouze, Piobert, Vankerchoff, and others. 



Von Lenk's system of manufacturing gun-cotton is briefly as follows : 



' 1. The carded cotton is spun into a loose yarn, varying in size and strength 

 according to the applications it is to receive ; and the yarn is made up into hanks of 

 convenient size (weighing about three ounces). 



1 2. The cotton is submitted to preliminary purification, by boiling it for a few 

 minutes in a solution of potassic carbonate, of specific gravity 1*02, separating tho 

 alkaline liquid by means of & centrifugul extractor, and washing the cotton thoroughly 

 in water. 



1 3. Tho cotton is perfectly dried by artificial heat, immediately before its treatment 

 with acid. 



' 4. Tho acid used for the production of the gun-cotton is prepared by mixing one 

 part by weight of nitric acid (of specific gravity T52) with three parts of sulphuric acid 

 (of specific gravity 1*84). This mixture is allowed to become perfectly cold before use. 



J 6. The ary cotton is immersed by small quantities (about six ounces, or two hanks 

 nt one time) in a bath of tho mixed acids, which is kept as cool as possible. When 

 the cotton has become thoroughly saturated, and has been moved about in the acid 

 for a few minutes, it is removed from tho bath to a ledge placed over it, where a 

 portion of the acid absorbed is separated by gentle pressure. Tho hanks are then 

 transferred to small covered stoneware vessels, in which they are presorvod for forty- 

 eight hours ; the proportion of acid with which they aro allowed to remain saturated 

 for that period being 10*5 parts by weight to 1 of the original cotton. The vessels 

 containing the gun-cotton and acid are kept as cool as possible by being surrounded 

 with water. 



' 6. The acid removed from the bath by each successive quantity of cotton immersed 

 is replaced by the addition of a corresponding quantity of tho fresh mixture, before 

 another quantity of cotton is treated. 



