separate the two layers, the tank is provided with an exit in the side,
near the bottom, closed by a sluice or valve. This valve is opened, and
the watery portion is allowed to escape into a sand filter bed.

The filter serves to retain any solid impurities which may still remain
suspended in the water; but it will be found that the escaping water is
nearly pure.

The dark brown fatty acid is mixed with a large amount of impurity, such
as short wool fibers, burrs, sand, and dye stuffs washed from the wool.
To remove water more completely, the semi-fluid mass is pumped from the
tank, and delivered into hair-cloth filters; the liquid which drains
from these bags finds its ways to the sand filters joining the drainage
which formerly passed out from the tank through the sluice. After being
turned over in the filter several times, the residue is transferred to
canvas sacks. These sacks are placed in a filter press, where they are
exposed to pressure while heated to a temperature sufficient to melt
the fat. The solid impurities remain in the bags, while the fatty acids
escape, and are received in a barrel or tank for the purpose. The fatty
acids, when cold, are of a deep brown color, and of the consistency
of butter. The residue is kept, and the method of treating it for the
recovery of indigo will afterward be described.

The fatty acids are now ready for conversion into soap. It may here be
remarked that, on distillation, they yield a nearly white fatty mass,
which, when treated with soda-lye, is capable of yielding a perfectly
white soap. But, for the clothworker's purpose, this purification is
unnecessary.

The conversion into soap is a very simple matter. As the fats are