Improvements relating to the Manufacture of Soap.
Year: 1892

page_text: Date of Application, 1st Dec., 1892-Accepted. 7th Jan., 1893
COMPLETE SPECIFICATION.
[Communicated from abroad by GEORG SCHICHT, of Aussig on the Elbe, in the
Empire of Austria-Hungary.]
Improvements relating to the Manufacture of Soap.
I, HENRY HARRIS LAKE, of the firm of Haseltine, Lake & Co., Patent Agents,
45 Southampton Buildings, in the County of Middlesex, do hereby declare the
nature of this invention and in what manner the same is to be performed, to be
particularly described and ascertained in and by the following statement :-
My invention relates to the manufacture of soap.
For making hard potash soap and potash-soda soap it is necessary to use a very
concentrated caustic alkali and to saponify the latter with the fat at as high a
temperature as practicable. Up to the present time this saponification has been
effected by causing the concentrated caustic potash or a mixture of potash and soda
to flow into the strongly heated fat. This however presents the inconvenience that
the fat, owing to the high temperature to which it has to be heated in order to
obtain a hard product, becomes brown and attacks by the free fatty acid, which is
either produced in consequence of the great heat necessary, or exists already in the
fat, the sides of the boiler consisting mostly of copper or iron, with formation of
sebates. Accordingly this method of causing the caustic potash or mixture of potash
and soda to flow into the heated fat, gives rise to two inconveniences, that is to say,
the finished soap, by reason of the fat becoming brown, obtains a comparatively
dark colour; and it is polluted by the sebacic metallic oxides (green copper sebate
or rust-brown iron sebate) which in the use of the soap gives rise to an insoluble
residue often colouring even the articles to be washed, particularly clothing.
In order to obviate these inconveniences I modify the customary method of
manufacturing hard potash and potash-soda soap in such a manner that the con-
centrated caustic alkali is not caused to flow into the highly heated fat, but that
a thin jet of the fat is caused to pass into the highly heated caustic alkali while
the material is rapidly stirred. Prior to being poured into the liquor the fat is
heated to a temperature below that at which the browning begins and as at the
instant when the fat meets with the large excess of the caustic alkali the saponifica-
tion takes place, the browning cannot occur subsequently, because the finished
soap can be subjected to a much higher temperature than the fat without under-
going deleterious changes. Moreover by the flow of the fat into the caustic
alkali and by the direct saponification of the fat, a contact of the fatty acids,
which may be contained in the fat or formed during the application of the heat,
with the metallic sides of the boiler is entirely obviated so that the formation
of copper sebate or iron sebate and the consequent pollution of the soap will be
prevented.
In practice my above described method may be carried out in the following
manner:
Concentrated caustic alkali is heated in the soap boiler to about 135 degrees
centigrade or weak liquor is evaporated until it reaches this boiling point. At the
same time the fat is heated in a separate vessel to from about 80 to 100 degrees
and introduced in thin jets into the caustic alkali. By means of mechanical stirrers
the entire material in the soap boiler is kept in continual motion, thereby effecting
an immediate and intimate mixing of the fat as it flows in with the alkaline liquor.
Having now particularly described and ascertained the nature of the invention
and in what manner the same is to be performed, as communicated to me by
my foreign correspondent, I declare that what I claim is :-
A method of manufacturing hard potash soap and potash soda soap, which

page_text: consists in heating a concentrated solution of caustic potash or of potash and soda
to a temperature of about 135 degrees centigrade and causing fat to pass in the
form of a thin jet into the said liquor while continually stirring, for the purpose set
forth.
Dated this 1st day of December 1892.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.