obtained which may be again used in scouring (p. 029)
wool.

[Illustration: Fig. 8.--Cloth-washing Machine.]

#Bleaching Wool.#--The wool fibre has to be treated very differently
from cotton fibre. It will not stand the action of as powerful
bleaching agents, and, consequently, weaker ones must be used. This is
a decided disadvantage, for whereas with cotton the colouring matter
is effectually destroyed, so that the bleached cotton never regains
its original colour, the same is not the case with wool, especially
with sulphur-bleached wool, here the colouring matter of the fibre is,
as it were, only hidden, and will under certain circumstances return.
The two materials chiefly used for bleaching wool are sulphur and
peroxide of hydrogen.

[Illustration: Fig. 9.--Sulphur Bleach House.]

#Sulphur Bleaching.#--Bleaching wool by sulphur is a comparatively (p. 030)
simple process. A sulphur house is built, the usual size being 12 feet
high by 12 feet broad, and about 17 feet long. Brick is the most suitable
material. The house should have well-fitting windows on two sides,
and good tight doors at the ends (see fig. 9). Some houses have a (p. 031)
small furnace at each corner for burning the sulphur, two of these
furnaces are fitted with hoods, so that the sulphur gases can be
conveyed to the upper part of the chamber, but a better plan, and one
mostly adopted where the chamber is used for bleaching pieces, is to
construct a false perforated bottom above the real bottom of the chamber,
the sulphur being burnt in the space between the two floors. If yarn
is being bleached the hanks are hung on wooden rods or poles in (p. 032)
the chamber, while with pieces an arrangement is constructed so that the
pieces which are stitched together are passed in a continuous manner
through the chamber.

When all is ready the chamber doors are closed, and the furnaces are
heated, some sulphur thrown upon them, which burning evolves sulphur
dioxide gas, sulphurous acid, and this acting upon the wool bleaches
it. The great thing is to cause a thorough circulation of the gas
through every part of the chamber, so that the yarn or pieces are
entirely exposed in every part to the bleaching action of the gas.
This is effected by causing the gas to pass into the chamber at
several points, and, seeing that it passes upwards, to the ventilator
in the roof of the chamber. Generally speaking, a certain quantity of
sulphur depending upon the quant