~Collodion-Cotton.~--In the manufacture of collodion or soluble cotton the
finer qualities of cotton-waste are used and the acids used in the dipping
tanks are much weaker. The manufacture of collodion-cotton has become of
more importance than gun-cotton, by reason of its use for the manufacture
of the various forms of gelatine, such as gelatine dynamite, gelignite,
forcite, &c., and also on account of its extensive use in the manufacture
of many of the smokeless powders. It is also used for the manufacture of
"collodion," which is a solution of collodion-cotton in ether-alcohol; for
the preparation of celluloid, and many other purposes. It is less
explosive than gun-cotton, and consists of the lower nitrates of
cellulose. It is soluble in nitro-glycerine, and in a mixture of 2 parts
of ether and 1 of alcohol; also in acetone, acetic ether, and other
solvents. MM. Ménard and Domonte were the first to prepare a soluble gun-
cotton, and its investigation was carried on by Béchamp, who showed that
its properties and composition were different to those of gun-cotton.

~Manufacture.~--The cotton used is cotton-waste.[A] It is thought by some
that Egyptian cotton is preferable, and especially long fibre varieties.
The strength of the acids used is, however, of more importance than the
quality of the cotton. The percentage composition of the acid mixture
which gives the best results is as follows:--Nitric acid, 23 per cent.;
sulphuric acid, 66 per cent.; and water, 11 per cent; and has a specific
gravity of 1.712 (about). It can be made by mixing sulphuric acid of
specific gravity 1.84 with nitric acid of specific gravity 1.368 in the
proportions of 66 per cent. and 34 per cent. respectively. (The production
of the penta-nitro-cellulose is aimed at if the collodion-cotton is for
use as an explosive.) If the acids are much weaker than this, or potassium
nitrate and sulphuric acid is used, the lower nitrates will be formed. The
product, while being entirely soluble in ether-alcohol or nitro-glycerine,