Illustration: CUTTING SOAP.
Illustration: COPPERS FOR THE MIXING PROCESS.
This very useful article is produced by a combination of tallow or
oil with soda or potash; with soda, hard soap is formed; with potash,
soft soap. The yellow soap of commerce has also an addition of resin
or turpentine, and often palm oil, these give it its yellow color
and peculiar smell; pure white soap is made by boiling a solution of
soda with tallow or olive oil; ordinary soaps are generally made by
mixing a solution of the soda of commerce, (carbonate of soda) with
quick lime, this takes away the carbonic acid and makes the soda what
is called “caustic;” this solution is drawn off, and kitchen stuff,
tallow, turpentine, and sometimes palm oil, are added and boiled
together, until all is converted into soap, but a large quantity of
water remaining, it is necessary to separate the soap from this, for
this purpose salt is added until the water becomes so heavy that the
soap rises to the surface, whence it is removed into moulds or frames
and allowed to cool, when it is cut into bars for sale.
Illustration: FILLING YELLOW SOAP.
Illustration: MOTTLED SOAP FRAMES.
Soft soap is made in the same way, using potash instead of soda,
and, generally, a large quantity of train-oil. Castile soap is pure
soda soap, and the blueish or red mottled appearance is produced by
stirring in some sulphate of iron (green vitriol); when new it is of
a blueish color, but gets red by exposure to the air.
Oils and fats combine with the oxides of several of the metals, and
a combination of oxide of lead with olive oil forms a firm solid
substance, or plaister, which, with the addition of a little resin,
is used in surgery, and when spread upon linen or calico, forms the
common adhesive plaister.
Oils and fats all consist of a combination of organic acids,
(stearic, oleic, and margaric), with glycerine. When these fats
are boiled with soda, potash, or metallic oxides, a combination of
the oxide and fatty acid takes place, and this constitutes soap.
The glycerine is then set free, and, when purified, forms a sweet,
oily, colorless fluid, very similar to syrup, but not so sweet; it
has lately been used for several purposes, especially as a remedy
for chapped hands; a soap called “glycerine soap,” has lately been
used for the same purpose; it is a soap made without separating the
glycerine.
Illustration: MACHINE FOR CUTTING SOAP IN BARS.
The above illustration represents an ingenious contrivance for the
purpose of cutting soap.