IMPROVEMENTS IN CONVERTING SKINS INTO LEATHER
Year: 1880

page_text: PROVISIONAL SPECIFICATION left by Richard Brown at the Office of
the Commissioners of Patents on the 11th September 1880.
RICHARD BROWN, of Ayr, in the County of Ayr, North Britain, Manufacturing
Chemist. "IMPROVEMENTS IN CONVERTING SKINS INTO LEATHER."
This Invention comprises improved processes to be substituted for the ordinary
tanning process of converting skins into leather, and it consists principally in
forming in the substance of the skins an insoluble chromate of lead or other
suitable metal.
In carrying out the Invention in the case of moderately thick skins, these are
first unhaired and subjected to the preliminary treatment usually employed
preparatory to tanning. The skins are first steeped for about 20 hours in a weak
solution of sulphuric, hydrochloric, oxalic, or acetic acid, the solution containing
about one part acid in one hundred parts water.
In the second stage the skins are steeped in a solution of five to tea parts
bichromate of potash or of soda in one hundred parts water, which is maintained
at a temperature of 80 to 100 degrees Fahrenheit. This steeping is continued for
about 24 hours, the skins being repeatedly turned over or suspended or otherwise
held or moved so as to insure thorough and uniform permeation of the solution.
The temperature is maintained by preference by a jet or jets of steam which has
also the advantage of agitating the liquid.
At the third stage the skins which have been treated as hereinbefore described
for the second stage are steeped in a solution of five to ten parts of acetate, or
nitrate, or chloride of lead, in a hundred parts water, which is maintained at a
temperature of 80 to 100 degrees Fahrenheit, maintained by preference by a jet or
jets of steam. This steeping may be continued for 24 to 48 hours, after which the
skins are treated with a very weak solution of a salt of iron, such as the sulphate.
Or this treatment with a salt of iron may be applied between the second and third
stages.
The skins are afterwards dried very slowly.
When at the first stage the skins are treated with hydrochloric, oxalic, or acetic
acid, the second and third stages may be transposed, the treatment with the
bichromate being made subsequent to that with a lead salt.

page_text: In some cases chlride of barium may be substituted for the lead salt, and when
hydrochloric acid is used at the first stage the treatment with chloride of barium
should precede that with bichromate of potash or of soda, but may follow it in other
cases.
The combinations of processes herein before described are suitable for heavy
leather, but when light or upper" leather is to be made the first stage treatment
with acid should be omitted, and in all cases the strengths and temperature of the
solutions and the durations of the steepings must be modified to suit differences in
the thickness or quality of the skins.
A bisulphate may be substituted for sulphuric acid in the first stage, and a
chromate may be substituted for the bichromate, allowance being made for the
different percentage of chromic acid therein, also in some cases chromic acid may
be used instead of a salt thereof.
Leather prepared according to any of the modifications hereinbefore described may
be subsequently treated with vaseline, or mineral oil, or petroleum, or an oil of
suitable consistency obtained therefrom.