382 CHEMICAL DISCOVERY AND INVENTION 



does not reach the maximum. Nitrocellulose having the com- 

 position expressed by the formula given above contains just over 

 14 per cent of nitrogen. Gun-cotton, however, usually contains 

 somewhat less than this percentage, namely, about 13-3 per cent, 

 owing probably to the presence of small quantities of one of the 

 lower nitrates, the formula of which has already been given. 



Generally speaking the lower nitrates are soluble in a mixture 

 of ether and alcohol, while gun-cotton is not dissolved by this 

 liquid. 



The solution of these lower nitrates in ether-alcohol constitutes 

 " collodion." It must be remembered that cotton is not strictly 

 speaking a definite chemical substance, and it varies somewhat 

 in physical state, and hence that cottons from different sources, 

 under the same conditions in a bath of the same composition, 

 while yielding nitrocellulose containing the same percentage of 

 nitrogen, may vary considerably in solubility. In the early 

 days a high degree of nitration, say 12-8 per cent of nitrogen or 

 upwards, was generally associated with insolubility in ether 

 alcohol, while lower content of nitrogen corresponded with greater 

 solubility. With greater experience, however, it is now possible 

 to produce nitrocellulose with a high percentage of nitrogen and 

 complete solubility in ether-alcohol. 



Gun-cotton requires a lower temperature than gunpowder 

 for its ignition. The rate at which it burns depends on the mode 

 of ignition and the conditions under which it is fired. A mass of 

 loose gun-cotton may be ignited on the open hand without 

 burning the skin or producing more than a momentary sensation 

 of warmth, while the same cotton lightly twisted would produce 

 a burn, and if confined in any sort of strong envelope would 

 explode. The difference consists in the rate at which decom- 

 position is transmitted through the mass, and the discovery that 

 the explosion of a detonating fuse containing fulminate of mercury 

 or some similar compound in contact with a mass of gun-cotton 

 would cause it also to explode was a step of great practical 

 importance. 



Nitroglycerine, a compound similar in constitution to nitro- 

 cellulose, both being nitrates, was discovered by Sobrero, an 

 Italian chemist, in 1847. Though its explosive properties were 

 known it was regarded as dangerous, and was not generally used 

 as a blasting agent till after 1867 when Alfred Nobel discovered 

 a method of rendering it portable and less dangerous by incor 



