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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
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