[Footnote A: Mr J.J. Sayers, in evidence before the court in the "Cordite Case," says he found 15.2 and 16.1 per cent. soluble cotton, and 13.07 and 13.08 per cent. nitrogen in two samples of Waltham Abbey gun-cotton.]
A whole series of nitrates of cellulose are supposed to exist, the highest member being the hexa-nitrate, and the lowest the mono-nitrate. Gun-cotton was at one time regarded as the tri-nitrate, and collodion-cotton as the di-nitrate and mono-nitrate, their respective formula being given as follows:—
Mono-nitro-cellulose C_{6}H_{9}(NO_{2})O_{5} = 6.763 per cent. nitrogen.
Di-nitro-cellulose C_{6}H_{8}(NO_{2}){2}O{5} = 11.11 " "
Tri-nitro-cellulose C_{6}H_{7}(NO_{2}){3}O{5} = 14.14 " "
But gun-cotton is now regarded as the hexa-nitrate, and collodion-cotton as a mixture of all the other nitrates. In fact, chemists are now more inclined to divide nitro-cellulose into the soluble and insoluble forms, the reason being that it is quite easy to make a nitro-cellulose entirely soluble in a mixture of ether-alcohol, and yet containing as high a percentage of nitrogen as 12.6; whereas the di-nitrate[A] should theoretically only contain 11.11 per cent. On the other hand, it is not possible to make gun-cotton with a higher percentage of nitrogen than about 13.7, even when it does not contain any nitro-cotton that is soluble in ether-alcohol.[B] The fact is that it is not at present possible to make a nitro-cellulose which shall be either entirely soluble or entirely insoluble, or which will contain the theoretical content of nitrogen to suit any of the above formulæ for the cellulose nitrates. Prof. G. Lunge gives the following list of nitration products of cellulose:—
[Footnote A: The penta-nitrate C_{12}H_{15}O_{5}(NO_{3})_{5} = 12.75 per cent. nitrogen.]
[Footnote B: In the Cordite Trial (1894) Sir F.A. Abel said, "Before 1888 there was a broad distinction between soluble and insoluble nitro- cellulose, collodion-cotton being soluble (in ether-alcohol) and gun-cotton insoluble." Sir H.E. Roscoe, "That he had been unable to make a nitro-cotton with a higher nitrogen content than 13.7." And Professor G. Lunge said, "Gun-cotton always contained soluble cotton, and vice versa." These opinions were also generally confirmed by Sir E. Frankland, Sir W. Crookes, Dr Armstrong, and others.]
Dodeca-nitro-cellulose C_{24}H_{28}O_{20}(NO_{2}){12} = 14.16 per cent.
nitrogen. (= old tri-nitro-cellulose)
Endeca-nitro-cellulose C{24}H_{29}O_{20}(NO_{2}){11} = 13.50 per cent.
nitrogen.
Deca-nitro-cellulose C{24}H_{30}O_{20}(NO_{2}){10} = 12.78 per cent.
nitrogen.
Ennea-nitro-cellulose C{24}H_{31}O_{20}(NO_{2}){9} = 11.98 per cent.
nitrogen.
Octo-nitro-cellulose C{24}H_{32}O_{20}(NO_{2}){8} = 11.13 per cent.
nitrogen. (= old di-nitro-cellulose)
Hepta-nitro-cellulose C{24}H_{33}O_{20}(NO_{2}){7} = 10.19 per cent.
nitrogen.
Hexa-nitro-cellulose C{24}H_{34}O_{20}(NO_{2}){6} = 9.17 per cent.
nitrogen.
Penta-nitro-cellulose C{24}H_{35}O_{20}(NO_{2}){5} = 8.04 per cent.
nitrogen.
Tetra-nitro-cellulose C{24}H_{36}O_{20}(NO_{2})_{4} = 6.77 per cent.
nitrogen. (= old mono-nitro-cellulose)
It is not unlikely that a long series of nitrates exists. It is at any rate certain that whatever strength of acids may be used, and whatever temperature or other conditions may be present during the nitration, that the product formed always consists of a mixture of the soluble and insoluble nitro-cellulose.
Theoretically 100 parts of cotton by weight should produce 218.4 parts of gun-cotton, but in practice the yield is a good deal less, both in the case of gun-cotton or collodion-cotton. In speaking of soluble and insoluble nitro-cellulose, it is their behaviour, when treated with a solution consisting of 2 parts ether and 1 of alcohol, that is referred to. There is, however, another very important difference, and that is their different solubility in nitro-glycerine. The lower nitrates or soluble form is soluble in nitro-glycerine under the influence of heat, a temperature of about 50° C. being required. At lower temperatures the dissolution is very imperfect indeed; and after the materials have been left in contact for days, the threads of the cotton can still be distinguished. The insoluble form or gun-cotton is entirely insoluble in nitro-glycerine. It can, however, be made to dissolve[A] by the aid of acetone or acetic ether. Both or rather all the forms of nitro-cellulose can be dissolved in acetone or acetic ether. They also dissolve in concentrated sulphuric acid, and the penta-nitrate in nitric acid at about 80° or 90° C.
[Footnote A: Or rather to form a transparent jelly.]