with nitric
acid for twenty or thirty minutes. They are characterised by being more
soluble than the higher nitrates and less inflammable. They are freely
soluble in a mixture of ether and alcohol, from which solutions they are
precipitated in a gelatinous form on adding chloroform. Acetic ether,
methyl alcohol, acetone and glacial acetic acid, will also dissolve
these nitrates.

Cellulose Di-nitrate, C{6}H{8}O{5}(NO{3}){2}, is obtained when
cellulose is treated with hot dilute nitric acid, or when the high
nitrates are boiled with solutions of caustic soda or caustic potash.
Like the last-mentioned nitrates it is soluble in a mixture of alcohol
and ether, in acetic ether, and in absolute alcohol. The solution of the
pyroxyline nitrates in ether and alcohol is known as collodion, and is
used in photography and in medical and surgical work.

One of the most interesting applications of the cellulose nitrates is in
the production of artificial silk. Several processes, the differences
between which are partly chemical and partly mechanical, have been
patented for the production of artificial silk, those of Lehner and of
Chardonnet being of most importance. They all depend upon the fact that
when a solution of cellulose nitrate is forced through a fine aperture
or tube, the solvent evaporates almost immediately, leaving a gelatinous
thread of the cellulose nitrate which is very tough and elastic, and
possesses a brilliant lustre. Chardonnet dissolves the cellulose nitrate
in a mixture of alcohol and ether, and the solution is forced through
fine capillary tubes into hot water, when the solvents immediately
evaporate, leaving the cellulose nitrate in the form of very fine fibre,
which by suitable machinery is drawn away as fast as it is formed.
Lehner's process is very similar to that of Chardonnet. Lehner uses a
solution of cellulose nitrate in ether and alcohol, and adds a small
quantity of sulphuric acid; by the adoption of the latter ingredient he
is able to use a stronger solution of cellulose nitrate, 10 to 15 per
cent., than would otherwise be possible, and thereby obtains a stronger
thread which resists the process of drawing much better than is the case
when only a weak solution in alcohol and ether is employed. By
subsequent treatment the fibre can be denitrated and so rendered less
inflammable.

The denitrated fibres thus prepared very closely resemble silk in their
lustre; they are not quite so soft and supple,