amount which would be paid were recovery not practiced. And lastly, the
streams are not polluted; the only waste is a little sulphate of soda,
which can hardly be regarded as a nuisance, inasmuch as it is a not
unfrequent constituent of many natural waters.

Let us now return to the solid matter from which the fatty acids have
been removed by pressure. This brown, earthly-looking cake consists of
vegetable impurity washed off from the cloth, of short fibers, and of
various dye stuffs. It is divided into two lots: That which contains
indigo, and that which contains none, or which contains too small a
quantity for profitable extraction. And it may here be remarked, that it
is advisable to collect the suds from cloth dyed with indigo separate
from that to dye which no indigo has been employed. The residue from
indigo-dyed cloth has always a more or less blue shade, and if much
indigo is present, the well-known copper-color is evident. Of course,
the amount of indigo must greatly vary, but it may rise to 8 or 10 per
cent. of the total weight of the refuse.

To recover the indigo from this refuse, the somewhat hard cakes are
broken up, placed in a tank, and allowed to steep in water. When quite
disintegrated, they are transferred to another tank--a barrel may be
used for small quantities--and thus this refuse is exposed to the
reducing action of copperas and lime. The indigo is converted into
indigo-white, and is rendered soluble, and it oxidizes on the surface,
forming a layer of blue froth on the top of the liquid, while the
remainder of the impurities sinks. This process of reduction may last
for twenty-four hours, and is helped by frequent stirring.

The indigo scum is preserved, and placed in filter cloths, where it is
thoroughly washed with water two or three times. The residue which has