448 GUN-COTTON AND NITRO-CELLULOSES. 



twisted into thread, it increases to 0'25; when subjected, in 

 the form of pulp, to hydraulic pressure, it becomes TO; but 

 these densities are apparent, the absolute density of gun-cotton 

 being 1'5. 



Nitrohydrocellulose prepared with cellulose disintegrated by 

 hydrochloric or sulphuric acid (A. Girard's process) has a 

 pulverulent form, which is very convenient for practical use. 

 Its composition and the force are the same as for gun-cotton. 



2. Gun-cotton is an extremely explosive compound, which is 

 ignited by contact with a heated body or by shock, or, again, 

 when it is raised to a temperature of 172. It burns suddenly, 

 with a large yellowish-red flame, but almost without smoke or 

 residue, and liberates a large volume of gas (carbonic acid, 

 carbonic oxide, nitrogen, steam, etc.). 



Compressed gun-cotton previously heated to 100 may explode 

 when ignited. It is, therefore, more liable than dynamite to 

 explode on simple inflammation. 



Gun-cotton kept at 80 to 100 decomposes slowly, and may 

 end by inflaming. 



It has been shown that a thin disc of compressed gun-cotton 

 may be pierced by a ball without explosion ; but if the thick- 

 ness of the disc be increased, or if resisting envelopes be used, 

 an explosion occurs. 



3. Sunlight causes it to undergo slow decomposition. 



4. Gun-cotton should be neutral to litmus, when it has been 

 carefully freed from all acid products by washing with alkali. 

 Nor should it emit acid fumes even, after keeping for some 

 time. A little sodium or ammonium carbonate is incorporated 

 with it to increase its stability. 



In the French navy, gun-cotton is submitted to a heat test, 

 which consists in heating it to 65, until it gives off sufficient 

 nitrous vapour to turn the iodised starch paper blue, or more 

 simply to redden litmus. It should stand this test for eleven 

 minutes. The heat test may be carried out either on the raw 

 material or on the washed product (the washing frees it from 

 alkaline carbonates), compressed between blotting paper, dried 

 at a low temperature, then left some time in the open air. 



5. The indefinite stability of gun-cotton has always been 

 regarded as doubtful, both by reason of its chemical constitution 

 and by the presence of the accessory products arising from the 

 original reaction or formed by accidental causes, which it is 

 hardly possible to avoid indefinitely. A slow decomposition 

 produced in this way sometimes becomes considerably accele- 

 rated by the heat which it liberates and by the reaction of the 

 products originally formed on the rest. It may become violent, 

 and end by exploding (see p. 45). 



Nevertheless, gun-cotton has been preserved for ten years 

 and more without any alteration. It has also been kept dry on 



