iquor it absorbs mechanically some of it,
and this amount may be roughly put down as about its own weight; thus
100 lb. weight of cotton will take up 10 gallons of liquor and carry
that quantity out of the bath. To some extent this may be minimised by a
previous wetting out of the cotton, which will then have in it as much
liquor as it will take up, and so practically no more will be taken up
from the dye-bath. Any loss of volume which may thus occur can be
remedied by the addition of water.

The dye-baths containing in solution, in addition to the dye-stuff,
salt, or Glauber's salt, or any other added substance, the cotton in
taking up the dye liquor will of course take up some of these in
proportion to the volume of liquor absorbed. The amount may range from 4
oz. to 1 lb. per gallon of liquor, and if 100 lb. cotton is being dyed
and takes up from 10 to 15 gallons of liquor, it is obvious that it must
absorb from 3 to 10 lb. of saline matter, and as the salinity of the dye
liquor is of some importance in dyeing direct colours, in making up the
bath for the next lot of cotton this must be allowed for and suitable
additions made. In order to do this properly it is a good plan to rely
upon the Twaddell.

The dyer should take the Twaddell of his bath before use and always make
up his baths to that strength. This will be found to range from 3 deg. to
12 deg. Tw.

Thus, for instance, a dye-bath made from 120 gallons of water with 20
lb. to 25 lb. common salt or Glauber's salt with the dye-stuffs will
stand at 4 deg. Tw., one made with 50 lb. common salt or Glauber's salt at
8 deg. Tw., while one which is made with 80 lb. to 100 lb. salt will stand
at 12 deg. to 13 deg. Tw. If the dyer always maintains his liquors at one
uniform degree Twaddell he can invariably depend upon getting uniform
shades from his dye-baths. This uniform strength is attained by adding
more salt or more water as the case may require.

Of course the continuous working of dye-baths cannot go on for ever;
sooner or later the baths become thick and dirty, and then they must be
thrown away and a new bath started.

(2) DIRECT DYEING FOLLOWED BY FIXATION WITH METALLIC SALTS.

It is an acknowledged principle in dyeing that to produce colours fast
to washing, soaping and rubbing, there must be produced on the fibre an
insoluble coloured substance. Now as the direct dyes do not essentially
produce such insoluble bodies when dyed on the cotton, the colou