Total ash 0.25 "

The soluble cotton, which is a mixture of the tetra- and penta-nitrates,
is soluble in ether-alcohol, and also in nitro-glycerine, and many other
solvents, whereas the hexa-nitrate (gun-cotton),
C_{12}H_{14}O_{4}(ONO_{2})_{6}, is not soluble in the above liquids,
although it is soluble in acetone or acetic ether. It is very essential,
therefore, that the nitro-cotton used in the manufacture of the gelatine
explosives should be as free as possible from gun-cotton, otherwise little
lumps of undissolved nitro-cotton will be left in the finished gelatine.
The non-nitrated or unconverted cotton should also be very low, in fact
considerably under 1/2 per cent.

The nitro-cotton and the nitro-glycerine used should always be tested
before use by the heat test, because if they do not separately stand this
test, it cannot be expected that the gelatine made from them will do so.
It often occurs, however, that although both the ingredients stand this
test separately before being mixed, that after the process of manufacture
one or other or both fail to do so.

The nitro-cotton most suitable for gelatine making is that which has been
finely pulped. If it is not already fine enough, it must be passed through
a fine brass wire sieve. It will be found that it requires to be rubbed
through by hand, and will not go through at all if in the least degree
damp. It is better, therefore, to dry it first. The percentage of nitrogen
in the nitrated cotton should be over 11 per cent. It should be as free as
possible from sand or grit, and should give but little ash upon ignition,
not more than 0.25 per cent. The cotton, which is generally packed wet in
zinc-lined wooden boxes, will require to be dried, as it is very essential
indeed that none of the materials used in the manufacture of gelatine