d a limited use for
intermixing with soft soaps.

It will be readily understood that hard and fast rules cannot be laid
down for "liquoring" soap, and the correct solution to be employed can
only be ascertained by experiment and experience, but the above
suggestions will prove useful as a guide towards good results. A smooth,
firm soap of clear, bright, glossy appearance is what should be aimed
at.

_Filling._--Some low-grade soaps contain filling, which serves no useful
purpose beyond the addition of weight. Talc is the most frequently used
article of this description. It consists of hydrated silicate of
magnesium and, when finely ground, is white and greasy to the touch. The
addition of this substance to the hot soap is made by suspending it in
silicate of soda solution.

Whatever filling material is used, it is important that the appearance
of the soap should not be materially altered.

_Neutralising, Colouring and Perfuming._--The free caustic alkali in
soap, intended for toilet or laundry purposes, is usually neutralised
during the cleansing, although some soap manufacturers prefer to
accomplish this during the milling operation. Various materials have
been recommended for the purpose, those in most general use being sodium
bicarbonate, boric acid, cocoa-nut oil, stearic acid, and oleic acid.

The best method is the addition of an exact quantity of sodium
bicarbonate (acid sodium carbonate), which converts the caustic alkali
into carbonate. The reaction may be expressed by the equation:--

NaOH + NaHCO_{3} = Na_{2}CO_{3} + H_{2}O
Caustic soda Bicarbonate of soda Carbonate of soda Water

Boric acid in aqueous or glycerine solutions, and borax (biborate of
soda) are sometimes used, but care is necessary in employing these
substances, as any excess is liable to decompose the soap.

The addition of cocoa-nut oil is unsatisfactory, the great objection
being that complete saponification is difficult to ensure, and, further,
there is always the liability of rancidity developing. Stearic and oleic
acids are more suitable for the purpose, but oleic acid has the
disadvantage that oleates are very liable to go rancid.

A large number of other substances have been proposed, and in many
instances patented, for neutralising the free caustic alkali. Among
these may be mentioned--Alder Wright's method of using an ammoniacal
salt, the acid radicle of which neutralises the caustic alkali,