s of a
solution of either salt, carbonate of soda, or silicate of soda, without
separation, and will retain its firmness. These materials are,
therefore, particularly adapted for the manufacture of marine soaps,
which often contain as much as 80 per cent. of water, and, being soluble
in brine, are capable of use in sea-water. For the same reason,
cocoa-nut oil enters largely into the constitution of hydrated soaps,
but the desired yield or grade of soap allows of a variation in the
choice of materials. Whilst marine soap, for example, is usually made
from cocoa-nut oil or palm-kernel oil only, a charge of 2/3 cocoa-nut
oil and 1/3 tallow, or even 2/3 tallow and 1/3 cocoa-nut oil, will
produce a paste which can carry the solutions of silicate, carbonate,
and salt without separation, and yield a smooth, firm soap.

The fatty materials, carefully strained and freed from particles of dirt
and fibre, are boiled with weak caustic soda lye until combination has
taken place. Saponification being complete, the solution of salt is
added, then the carbonate of soda solution, and finally the silicate of
soda solution, after which the soap is boiled. When thoroughly mixed,
steam is shut off, and the soap is ready for framing.

The marbled hydrated soap is made from cocoa-nut oil or a mixture of
palm-kernel oil and cocoa-nut oil with the aid of caustic soda lye
32-1/2 deg. Tw. (20 deg. B.). As soon as saponification is complete, the brine
and carbonate of soda solution are added, and the pan allowed to rest.

The soap is then carefully tasted as to its suitability for marbling by
taking samples and mixing with the colouring solution (ultramarine mixed
with water or silicate of soda solution). If the sample becomes blue
throughout, the soap is too alkaline; if the colour is precipitated, the
soap is deficient in alkali. The right point has been reached when the
marbling is distributed evenly. Having thus ascertained the condition of
the pan, and corrected it if necessary, the colour, mixed in water or in
silicate of soda solution, is added and the soap framed.

(D) _Treatment of Fat with Indefinite Amount of Alkali and Separation of
Waste Lye._--This is the most general method of soap-making. The various
operations are:--

(_a_) Pasting or saponification.
(_b_) Graining out or separation.
(_c_) Boiling on strength.

And in the case of milling soap base and household soaps,

(_d_) Fitting