almost impossible (at any rate upon the manufacturing scale) to make pure
hexa-nitro-cellulose or gun-cotton; it is certain to contain several per
cents. of the soluble forms, i.e., lower nitrates. It often contains as
much as 15 or 16 per cent., and only from 13.07[A] to 13.6 per cent. of
nitrogen.

[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