gths.

The saponification by means of carbonated alkali may be performed in an
open vat containing a steam coil, or in a pan provided with a removable
agitator.

It is usual to take soda ash (58 deg.), amounting to 19 per cent. of the
weight of fatty acids to be saponified, and dissolve it in water by the
aid of steam until the density of the solution is 53 deg. Tw. (30 deg. B.); then
bring to the boil, and, whilst boiling, add the molten fatty acids
slowly, but not continuously.

Combination takes place immediately with evolution of carbonic acid gas,
which causes the contents of the vat or pan to swell, and frequently to
boil over. The use of the agitator, or the cessation of the flow of
fatty acids, will sometimes tend to prevent the boiling over. It is
imperative that the steam should not be checked but boiling continued
as vigorously as possible until all the alkali has been absorbed and the
gas driven off.

The use of air to replace steam in expelling the carbonic acid gas has
been patented (Fr. Pat. 333,974, 1903).

A better method of procedure, however, is to commence with a solution of
64 deg. Tw. (35 deg. B.) density, made from half the requisite soda ash (9-1/2
per cent.), and when this amount of alkali has all been taken up by the
fatty acids (which have been added gradually and with continuous
boiling), the remaining quantity of soda ash is added in a dry state,
being sprinkled over each further addition of fatty acid.

This allows the process to be more easily controlled and boiling over is
avoided.

It is essential that the boiling by steam should be well maintained
throughout the process until all carbonic acid gas has been thoroughly
expelled; when that point is reached, the steam may be lessened and the
contents of the vat or pan gently boiled "on strength" with a little
caustic lye until it ceases to absorb caustic alkali, the soap being
finished in the manner described under (D).

It is extremely difficult to prevent discoloration of fatty acids, hence
the products of saponification in this way do not compare favourably in
appearance with those produced from the original neutral oil or fat.

(B) _Treatment of Fat with Definite Amount of Alkali and no Separation
of Waste Lye._--Cold-process soap is a type of this class, and its
method of production is based upon the characteristic property which the
glycerides of the lower fatty acids (members of the cocoa-nut-oil class)
possess of readily