Improvements in the Art or Process of Tanning Hides or Skins.
Year: 1893

page_text: Date of Application, 19th Dec., 1893-Accepted, 9th June, 1894
COMPLETE SPECIFICATION.
Improvements in the Art or Process of Tanning Hides or Skins.
I, WILLIAM ZAHN, of Nos. 309 to 327 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 my invention, and in what manner
the same is to be performed, to be particularly described and ascertained in and
by the following statement :-
The invention relates to a novel process for tanning skins or hides, and consists
in subjecting the skins or hides to the action of certain metallic compounds, which
are offered to the skins in two baths, and whereby, by exposing the skins or hides
to the action of the chemical compositions, the leather is rendered not only water-
proof, soft and flexible, but a leather of higher superiority in quality is the result,
than leather made by other similar processes.
In order that a clear understanding may be had of my present invention and the
manner in which the same is to be put into practice, I will now give a description
of the same.
For preparing the skins and hides and producing a strong, flexible and water-
proof leather in a much shorter time than heretofore, I subject the skins or hides,
after the raw hide has been prepared in the ordinary manner for tanning, to two
baths. The first bath consists of a weak, preferably a % solution of chromic
acid or its equivalent. The previously prepared skins or hides are placed in this
solution, and after they have been left therein for from one to three hours or more,
according to the thickness of the skins so as to be thoroughly impregnated by the
solution, they are removed therefrom and drained and the surplus water is
pressed out.
The skins or hides are then transferred to the second bath, which consists
essentially of a chromic oxide salt and a sulphide of an alkali, or a suitable sulphide
of an earth alkali.
For the chromic oxide salt I prefer to use chrome alum and for the sulphide I
may use sulphide of sodium or sulphide of potassium.
The required amount of chrome alum, about 70 or 80 pounds, for one thousand
pounds of skin, is dissolved in as much water as is necessary to cover the skins.
The said skins are now placed into this bath and while the wheels of a paddle are
put in motion, the sulphide of an alkali or an earth alkali is added. The sulphide
converts the chrome alum into a basic salt and the sulphuretted hydrogen which is
liberated, reduces the chromic acid absorbed by the skin, in the first bath, to
chromic oxide, and which oxide in "statu nascendo" combines with the basic salt
and forms chromium hydrate.
The hides or skins are left in this bath from 10 to 15 hours according to their
thickness, and are then removed, washed and finished in the ordinary manner.
The liquor in which the skins are placed may be analyzed after their removal
therefrom and brought to the proper concentration required, when the baths can
be used for the treatment of the second batch of skins or hides, as will be evident.
The leather produced in this manner is very soft, elastic, strong and water-
proof.
Of course I am aware that some of the substances named hereinabove have been
used before, but never before, to my knowledge, in the combination hereinabove
described, and the sulphide of an alkali or earth alkali has not been used before for
the purposes herein set forth.

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 :-
1. In the art of tanning hides or skins, the herein described process, which
consists in treating the same with a bath comprising therein a composition consisting
of chromic oxide salts and adding a sulphide of an alkali or an earth alkali, for the
purposes set forth.
2. In the art of tanning skins or hides, the herein described composition
consisting of chrome alum, sulphide of sodium and sulphide of potassium,
substantially as set forth.
3. In the art of tanning skins or hides, the herein described composition
consisting of chrome alum, and a sulphide of an alkali or earth alkali, substantially
as set forth.
DL
1 1
7
1009
WILLIAM ZAHN.
Haseltine, Lake & Co.,
45, Southampton Buildings, London, Agents for the Applicant.