is finished, the dye-bath is charged with a large quantity
of colouring matter in an unusable form which has to be thrown away,
thus at once adding to the pollution of the river into which it is
run, and to the cost of the process of dyeing. As attention is being
directed more and more to the question of the prevention of pollution
of rivers, and as the waste liquors from dye-works add to the apparent
pollution to a very considerable extent, dyers will have to develop
other modes of dyeing than that of stuffing and saddening in one bath.

The principle of dyeing by stuffing and saddening may be carried (p. 076)
out by the use of two separate baths; in fact, it is done in the case
of dyeing a cutch brown from cutch and bichromate of potash. The goods
are first treated in a bath of the dye-wood for a short time, then
rinsed, and the colour is developed by padding into a saddening bath
of the mordant. By this method the baths, which are never quite
exhausted, can be retained for future use, only requiring about 1/2 to
3/4 of the original quantities to be added for each succeeding batch
of the goods, in fact, in some cases, as in cutch, old baths work
better than new ones.

The advantage attached to this method of working is that arising from
economy of dye-stuff and mordant, and the reduction of the pollution
of the stream on which the works are situated. The disadvantages are
that the cost of labour is increased by there being two baths instead
of one, and that the shades obtained are not always so full as with
the one-bath method. This, of course, can be remedied by running the
goods through the baths again, which, however, adds to the cost of the
process, but there is this much to be said, the shade can be better
brought up than by the one-bath process. In some cases the methods of
mordanting, dyeing and saddening are combined together in the dyeing
of wool, thus, for instance, a brown can be dyed by first mordanting
with bichrome, then dyeing with camwood and saddening in the same bath
with copperas. The shades obtained are fairly fast and will stand
milling. The disadvantages of this process are the same as those
attached to the dyeing and saddening in one bath.

Now we come to the last method of dyeing wool with mordant and colours,
that in which the operation is carried out in one bath. This can only
be done in those cases where the colour lake that is formed is somewhat
soluble in dye-liquors, which usually ha