must never be
omitted, even for dark shades, as the traces of grease which the fibre
contains are the causes of nearly irremediable stains in the dyeing
operations. Even in dyeing black wool it is of the greatest importance
to have the fibre suitably scoured.

The fatty matters which the fibre contains may belong to the
components of the fibre itself and be natural matters, but in the case
of wool yarns and cloths they are mostly dressing oils, from which the
dyer cannot be too anxious to free the wool before dyeing. Some
practical methods of preparatory treatment of the fibres before dyeing
may therefore be described here with advantage.

Cotton is boiled off at actual boiling heat for two hours, with 8 per
cent. of its weight of carbonate of soda and a little soft soap, which
treatment is sufficient for dark colours.

For light colours it is necessary that the cotton be bleached. Wool is
scoured with soda and soap in the proportion of 10 lb. soda and 2 lb.
Marseilles soap for 100 lb. wool. Silk is scoured by boiling for one
and a half hours in a boiling bath with 30 per cent. of its weight of
soap. For light colours a second boiling should be given, with 15 per
cent.

The careful cleaning of wool previous to dyeing is of exceptional
importance. Raw wool is cleaned with carbonate of soda and ammonia. For
50 lb. wool to be cleaned 6 lb. carbonate of soda and 1-1/2 lb. (p. 079)
ammonia are added to a bath of 150 gallons water. The wool is laid
down in it for twenty minutes at 35 deg. C., taken up, squeezed, treated
for fifteen minutes in another bath, with 5 lb. carbonate of soda and
then rinsed. The first bath must be renewed as often as possible,
because it contains all the impurities. In the case of woollen yarn
30 lb. require two tubs of 40 gallons capacity. The first tub is to
contain 35 gallons water and 2 lb. ammonia at 10 deg. Be. After working
the skeins for three minutes in it they are left to stand for fifteen
minutes, then wrung out, and the operation is repeated in the second
tub. Finally, the yarn is rinsed several times in soft water.

Woollen piece goods are treated in a large wooden tub at 40 deg. C. with
4 lb. carbonate of soda and 2 lb. carbonate of ammonia for 80 lb.
material. The pieces are moved about for twenty minutes, laid down in
the bath overnight, again turned for ten minutes and hydro-extracted.
They may also be handled for forty minutes in a bath of 2 oz. ammonia
for 100 lb. wool at