The Dyeing of Cotton Fabrics | Page 6

and magnesium chlorides, etc., in the
treatment of cotton fabrics; as in finishing processes, where the goods
are dried afterwards, there is a great liability to form hydrocellulose
with the accompaniment of the tendering of the goods.
ACTION OF NITRIC ACID.
The action of nitric acid on cellulose is a variable one, depending on
many factors, strength of acid, duration of action and temperature.
Naturally as nitric acid is a strong oxidising agent the action of nitric
acid on cellulose is essentially in all cases that of an oxidant, but the
character of the product which is obtained varies very much according
to the conditions just noted. When cellulose or cotton in any form is
immersed in nitric acid of 1.4 to 1.5 specific gravity for a moment, and
the fibre be well washed, there is a formation of hydrate of cellulose
which has a gelatinous nature. This is deposited on the rest of the
material, which is not materially affected so far as regards strength and
appearance, but its power of affinity for dyes is materially increased.
There is some shrinkage in the size of the cotton or paper acted upon.
Nitric acid changes all kinds of cellulose into nitro products, the
composition of which depends upon the strength of the acid, the
duration of treatment, and one or two other factors. The nitrocelluloses
are all highly inflammable bodies, the more highly nitrated burning
with explosive force. They are produced commercially and are known
as "gun cotton" or "pyroxyline". The most highly nitrated body forms
the basis of the explosive variety; the least highly nitrated forms that of
the soluble gun cotton used for making collodion for photographic and
other purposes.
The products formed by the action of nitric acid are usually considered
to be nitrocelluloses. It would appear that they are more correctly
described as cellulose-nitrates, for analysis indicates the presence of the
NO{3} group, which is characteristic of nitrates, and not of the NO{2}
group, which is the feature of nitro bodies in general. Further, nitro

compounds, when subject to the action of reducing agents, are
converted into amido compounds, as is the case, for instance, with
nitro-benzene, C{6}H{5}NO{2}, into aniline, C{6}H{5}NH{2}, or
with nitro-naphthalene, C{10}H{7}NO{2}, which changes into
naphthylamine, C{10}H{7}NH{2}.
But the nitric acid derivatives of cellulose are not capable of conversion
by reducing agents into similar amido compounds. They have the
following properties, which accord more closely with nitrates than with
nitric bodies: alkalies remove the nitric acid; cold sulphuric acid expels
the nitric acid, cellulose sulphates being formed; boiling with ferrous
sulphate and hydrochloric acid causes the elimination of the nitric acid
as nitric oxide (on which reaction a method for determining the degree
of nitration of gun cotton is based). It is best therefore to consider them
as cellulose nitrates. Several well-characterised cellulose nitrates have
been prepared, but is an exceedingly difficult matter to obtain any one
in a state of purity, the commercial articles being always mixtures of
two or three. Those that are best known and of the most importance are
the following:--
Cellulose Hexa-nitrate, C{6}H{4}O{5}(NO{3}){6}. This forms the
principal portion of the commercial explosive gun cotton, and is made
when a mixture of strong nitric acid and strong sulphuric acid is
allowed to act on cotton at from 50 to 55° F. for twenty-four hours. The
longer the action is prolonged, the more completely is the cotton
converted into the nitrate, with a short duration the finished product
contains lower nitrates. This hexa-nitrate is insoluble in ether, alcohol,
or in a mixture of those solvents, likewise in glacial acetic acid or in
methyl alcohol.
Cellulose Penta-nitrate, C{6}H{5}O{5}(NO{3}){5}, is found in
explosive gun cotton to a small extent. When gun cotton is dissolved in
nitric acid and sulphuric acid is added, the penta-nitrate is thrown down
as a precipitate. It is not soluble in alcohol, but is so in a mixture of
ether and alcohol, it is also slightly soluble in acetic acid. Solutions of
caustic potash convert it into the di-nitrate.
Cellulose Tetra-nitrate, C{6}H{6}O{5}(NO{3}){4}, and Cellulose

Tri-nitrate, C{6}H{7}O{5},(NO{3}){3}, form the basis of the
pyroxyline or soluble gun cotton of commerce. It has not been found
possible to separate them owing to their behaviour to solvents being
very similar. These nitrates are obtained by treating cotton 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