s made cold with the
required amount of dye-stuff and not too small a quantity of water, the
cotton is immersed and worked for a short time to ensure impregnation,
then the temperature is slowly raised to the boil. This operation should
be carefully carried out, inasmuch as time is an important element in
the dyeing with mordant colours; the colouring principle contained in
the dye-stuff must enter into a chemical combination with the mordant
that has been fixed on the fibre. Heat greatly assists this being
brought about, but if the operation is carried on too quickly, then
there is a tendency for uneven shades to be formed. This can only be
remedied by keeping the temperature low until the dye-stuff has been
fairly well united with the mordant, and then maintaining the heat at
the boil to ensure complete formation of the colouring lake on the
fibre, and therefore the production of fast colours.

It has been noticed in the dyeing of alizarines on both cotton and wool
that when, owing to a variety of circumstances, local overheating of the
bath happens to take place dark strains or streaks are sure to be
formed. To avoid these care should be taken that no such local heating
can occur.

It only remains to add that it is possible to dye a great range of
shades by this method, reds with alizarine and alumina; blacks with
logwood and iron; greens from logwood, fustic, or Persian berries, with
chrome and iron; blues from alizarine blues; greens from Coeruleine or
Dinitrosoresorcine, etc.

Another method of mordanting cotton for the mordant group of dye-stuffs
is that in which the cotton is impregnated with a salt of the mordant
oxide derived from a volatile acid such as acetic acid, and then
subjected to heat or steaming. This method is largely taken advantage of
by calico printers for grounds, and dyers might make use of it to a much
larger extent than they do.

There are used in this process the acetates of iron, chromium and
aluminium, and bisulphites of the same metals and a few other compounds.
Baths of these are prepared, and the cotton is impregnated by steeping
in the usual way; then it is gently wrung out and aged, that is, hung up
in a warm room overnight. During this time the mordant penetrates more
thoroughly into the substance of the fabric, while the acid, being more
or less volatile, passes off--probably not entirely, but at any rate
some of the metal is left in the condition of oxide and the bulk of it
as