te of potash is a very powerful oxidising agent. On cellulose
neutral solutions have but little action, either in the cold or when
heated. They may, therefore, be used for the bleaching of cotton or
other cellulose fibres.

Alkaline solutions of permanganate convert the cellulose into
oxycellulose, which resembles the oxycellulose obtained by the action of
the nitric acid.

Chromic acid, when used in the form of a solution, has but little action
on cellulose. In the presence of mineral acids, and used warm or
boiling, chromic acid oxidises cellulose into oxycellulose and other
products.

It is therefore always advisable in carrying out any technical process
connected with cotton which involves its treatment with oxidising agents
of any kind, and where it is desired not to alter the cotton, to allow
these actions to be as short as possible.

=Dyes and Cotton Dyeing.=--An account of the chemistry of the cotton
fibre would not be complete unless something is said about the reactions
involved in the processes of dyeing and printing cotton. This is a most
interesting subject and opens up quite a number of problems relating to
the combination of the fibre with colouring matter of various kinds, but
here only a brief outline of the principles that present themselves in
considering the behaviour of the cotton fibre as regards colouring
matter will be given.

When the question is considered from a broad point of view, and having
regard to the various affinities of the dyes for cotton; we notice (1)
that there is a large number of dye-stuffs--the Benzo, Congo, Diamine,
Titan, Mikado, etc., dyes--that will dye the cotton from a plain bath or
from a bath containing salt, sodium sulphate, borax or similar salts;
(2) that there are dyes which, like Magenta, Safranine, Auramine and
Methyl violet, will not dye the cotton fibre direct, but require it to
be mordanted or prepared with tannic acid; (3) that there are some dyes
or rather colouring matters which, like Alizarine, Nitroso-resorcine,
barwood, logwood, etc., require alumina, chrome and iron mordants; (4)
that there are some dyes which, like the azo scarlet and azo colours in
general, cannot be used in cotton dyeing; (5) that there are a few dyes,
_i.e._, indigo, which do not come under this grouping.

From the results of recent investigations into the chemistry of dyeing
it is now considered that for perfect dyeing to take place there must be
formed on the fibre a combina