An Improved Process of Tawing Hides for making Kid-leather.
Year: 1892

page_text: Date of Application, 12th Apr., 1892-Accepted, 21st May, 1892
COMPLETE SPECIFICATION.
An Improved Process of Tawing Hides for making Kid-leather.
I, WILLIAM ZAHN, of No. 325 Academy Street, in the City of Newark, County
of Essex, and State of New Jersey, United States of America, Manufacturer
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 :-
This invention relates to an improved process of tawing hides for the purpose of
making kid-leather, which process consists in treating the hides with a solution of
chrome-salt and then subjecting the same to the action of sulphuretted hydrogen
either in the form of a gas or an aqueous solution of the same.
In carrying out the invention 100 pounds of well prepared hides are first immersed
into a solution composed of five pounds of bi-chromate of potash and two pounds of
common salt dissolved in five gallons of water, to which are added two and one half
pounds of commerical hydrochloric acid.
The hides remain in solution until the same appear to be well soaked, which
takes from three to five hours, or in the case of thin skins even less than three
hours. The excess of this preparatory liquor is then removed by spreading and
pressing, after which the skins are ready for the next treatment, which consists in
the application of the sulphuretted hydrogen, either alone or in conjunction with
other compounds. The sulphuretted hydrogen may be used either in gaseous form
or in an aqueous solution. If it be applied in the form of a gas, the skins are
suspended in a closed chamber, or in a series of chambers which are so connected
that each successive chamber receives the surplus of gas from the preceding one.
If a series of chambers is used, the surplus gas passes from the first chamber into
the second, from the second into the third, fourth, and so on. When the skins in
the first chamber are finished, which is indicated by the change of the yellow color
of the skins into a bluish color, the supply of the sulphuretted hydrogen to the first
chamber is interrupted and the same supplied to the second chamber. The skins
are then removed from the first chamber, which is refilled with untreated skins,
after which the chamber is connected with the fourth chamber so as to receive the
overflow of the third chamber, it becoming thereby the last chamber of the series
and receiving the overflow of the sulphuretted hydrogen.
The second chamber is next emptied and refilled with untreated skins after
which the connection with the first chamber is made so that the second chamber
becomes the last chamber, and so on, so that each chamber becomes in rotation the
first and last one of the series.
If the sulphuretted hydrogen be applied in an aqueous solution, the hides
after being treated as before described with a bi-cromate of potash solution,
are, after the excess of liquor has been removed, placed into a bath composed
of two pounds of yellow sulphuret of potash of commerce which are dissolved
in twelve gallons of water. To this solution are slowly added four pounds of
dilued sulphuric acid which is produced by mixing one pound of sulphuric acid
with five pounds of water. After the skins have been in this solution for some
time one pound of potassium sulphuret is added for the reason that if the entire
quantity of sulphuret should be directly dissolved in the bath, a too great
quantity of sulphuretted hydrogen would be liberated at once, so that a con-
siderable part of the same would be lost into the air owing to the limited
solubility of the sulphuretted hydrogen in water.
The skins are finished when their yellow color has been gradually changed
throughout into a bluish color. If it be desired to work alum into the skin,
the alum may be added to this bath.

page_text: Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
The process herein described of tawing hides, which consists in first treating
the same with a bath containing a chrome-salt, and the subjecting them to the
action of sulphuretted hydrogen, substantially as set forth.
Dated this 11th ...
M1000
WILLIAM ZAHN.
Haseltine, Lake & Co.,
45, Southampton Buildings, London, Agents for the Applicant.