c acid taken up
be regarded as the criterion of success.

In the natural products which have just been enumerated, the tannic acid
is accompanied by some colouring matter, which is also absorbed by the
cotton; in some (sumac and galls) this colour is present in but small
quantities; in others (divi-divi, myrabolams, algarobilla), there is a
large quantity; therefore cotton treated with these comes out more or
less coloured. Now it is obvious that such forms of tannin cannot be
used when light tints are to be dyed, for such the acid itself must be
used, for medium shades sumac or galls may be used; while when dark
shades--browns, maroons, dark greens, navy blues, etc., are to be dyed,
then such tannin matters as divi-divi or myrabolams may be conveniently
and economically adopted. The quantity used varies according to
circumstances; the character of the shades that are to be dyed, the
dye-stuff used, the quality and character of the tannin matter used. For
pale shades about 1 per cent. of tannic acid may be used, deep shades
require from 3 to 4 per cent. Of tannin matters from 5 per cent. may be
used for pale shades, from 20 to 25 per cent. for deep shades. The
tannin baths are not exhausted, and may be kept standing, adding for
each succeeding lot of cotton from 1/2 to 3/4 of the above quantities of
tannin matters. Of course sooner or later the baths become unusable from
various causes, and then they may be thrown away; but old tannin baths
often work better than the new ones.

(2) =The Fixing Bath.=--Following on the tannin bath comes the fixing
bath to fix the tannin on the cotton in the form of insoluble metallic
tannates. A variety of metallic salts may be used for this purpose,
those of antimony, tin, iron, lead, etc., the substances most commonly
used being tartar emetic, antimony fluoride, oxalate of antimony, tin
crystals and copperas.

Beyond forming the insoluble tannate of antimony or tin, as the case may
be, the salts of antimony and tin have no further effect on the tanned
cotton, and they may be used to fix the tannin for all tints or shades,
from very pale to very deep. Of all these salts tartar emetic has been
found to be the best, probably because it is the least acid in its
reactions, and therefore there is no tendency to remove any tannin from
the fibre, as is the case with the other salts. Tin salt is little used
for this purpose, because of its acidity, which prevents it from fixing
the tannin as