incorporated with a soap of a lower grade than the one
from which it was obtained. In this case a system is generally adopted;
for example, soap of the best quality is made in a clean pan, the nigre
remaining is worked up with fresh material for soap of the next quality,
the nigre from that boil, in its turn, is admixed with a charge to
produce a batch of third quality, and the deposited nigre from this is
again used for a fourth quality soap--the nigre obtained from this
latter boil would probably be transferred into the cheapened "washer" or
perhaps if it was dark in colour into the brown soap-pan.

(3) The nigre may be fitted and produce a soap similar to the original
soap from which it was deposited. It is advisable to saponify a little
fat with it.

(4) Nigres from several boils of the same kind of soap can be collected,
boiled, and fitted. The settled portion may be incorporated with a new
charging to keep the resultant soap uniform in colour--unless this is
done, the difference in colour between boils from new materials alone,
and those containing nigre, is very noticeable. The nigre settled from
this fitted nigre boil would be utilised in brown soap.

(5) According to its colour, and consistence, a nigre may be suitable
for the production of disinfectant, or cold-water soaps.

(6) Nigre may be bleached by treatment with a 20 per cent. solution of
stannous chloride--1 cwt. of this solution (previously heated) is
sufficient to bleach 20 tons of nigre.

_Transparent Soaps._--The production of transparent soaps has recently
been fully studied, from a theoretical point of view, by Richardson
(_J. Amer. Chem. Soc._, 1908, pp. 414-20), who concludes that the
function of substances inducing transparency, is to produce a jelly and
retard crystallisation.

The old-fashioned transparent soap is prepared by dissolving, previously
dried, genuine yellow soap in alcohol, and allowing the insoluble saline
impurities to be deposited and removed. The alcoholic soap solution is
then placed in a distillation apparatus, or the pan containing the
solution is attached by means of a still head to a condenser, and the
alcohol distilled, condensed and regained. The remaining liquid soap,
which may be coloured and perfumed, is run into frames and allowed to
solidify.

The resultant mass is somewhat turbid, but after storage in a room at
95 deg. F. (35 deg. C.) for several months, becomes transparent.

The formation of the transp