emicking,
and souring.

The next operation is the "grey sour," in which the goods are run
through a washing machine containing hydrochloric acid of 2 deg. Tw.
strength, with the object of dissolving out the lime which the goods
retain in considerable quantity after the lime boil. The goods are
then well washed, and are now boiled again in the ash bowking kier,
which is similar in construction to the lime kier, with soda ash (3%)
and a solution of rosin (1-1/2%) in caustic soda (1-1/4%) for eight to
ten hours. For white bleaching the rosin soap is omitted, soda ash
alone being employed.

[Illustration: FIG 5.--Roller Washing Machine.]

The pieces are now washed free from alkali and the bleaching proper or
"chemicking" follows. This operation may be effected in various ways,
but the most efficient is to run the goods in a washing machine
through bleaching powder solution at 1/2 deg.-1 deg. Tw., and allow
them to lie loosely piled over night, or in some cases for a longer
period. They are now washed, run through dilute sulphuric or
hydrochloric acid at 2 deg. Tw. ("white sour") and washed again.
Should the white not appear satisfactory at this stage (and this is
usually the case with very heavy or dense materials), they are boiled
again in soda ash, chemicked with bleaching powder at 1/8 deg. Tw. or
even weaker, soured and washed. It is of the utmost importance that
the final washing should be as thorough as possible, in order to
completely remove the acid, for if only small quantities of the latter
are left in the goods, they are liable to become tender in the
subsequent drying, through formation of hydrocellulose.

The modern processes of bleaching cotton pieces differ from the one
described above, chiefly in that the lime boil is entirely dispensed
with, its place being taken by a treatment in the kier with caustic
soda (or a mixture of caustic soda and soda ash) and resin soap. The
best known and probably the most widely practised of these processes
is one which was worked out by the late M. Horace Koechlin in
conjunction with Sir William Mather, and this differs from the old
process not only in the sequence of the operations but also in the
construction of the kier. This consists of a horizontal egg-ended
cylinder, and is shown in transverse and longitudinal sections in
figs. 6 and 7. One of the ends E constitutes a door which can be
rais