Improvements in and relating to a New and Useful Process of Chrome Tanning Leather and in and to the Article Produced thereby.
Year: 1889

page_text: COMPLETE SPECIFICATION.
Improvements in and relating to a New and Useful Process of
Chrome Tanning Leather and in and to the Article Produced
thereby.
I PETER JENSEN of 77 Chancery Lane in the County of London, Fellow of the
Institute of Patent Agents do hereby declare the nature of this invention and in
what manner the same is to be performed to be particularly described and ascer-
tained in and by the following statement, a communication to me from abroad by
David Pierson, Junior, of corner of Front and Monroe Streets, Wilmington, in the
County of Newcastle and State of Delaware, one of the United States of America,
gentleman
-
This invention relates to improvements in chrome tanned leather and in the art or
process of finishing the same, which consists in rendering it permanently soft and
flexible by charging and filling the pores with sesqui-oxide of chromium in a pure
state of minute division and perfectly cold, and causing it to receive, thoroughly and
quickly, and retain the color given to it after the filling operation, as I will now more
fully describe and explain, preparatory to a specific designation of the matters claimed
as my invention.
My invention has for its object to give a permanent softness and flexibility to tanned
leather and skins, without the aid of oils or greasy materials, and to give them a fixed
color, which will not change by contact with the air.
The process, which constitutes part of my invention, consists in the employment of
a chemical preparation, which operates upon the leather and skins in a manner entirely
different from the processes employed hitherto. For the purpose of rendering the
leather or skins soft and flexible, as well as durable, I employ the following process,
subsequent to the tanning process, viz. :---
I have various methods of obtaining the hydrated sesqui-oxide of chromium
(chromic hydrate) which forms the base of my process.
I will commence by describing the cheapest method, which consists in taking the
residue from bichromate batteries, and, by means of a carbonate of soda, precipitating
this chrome alum, which leaves the batteries, and I obtain two distinct products,
viz. a liquid sulphate of soda and a sesqui-oxide of chromium (chromic hydrate)
which by washing and decanting is rendered completely neutral; that is neither
alkaline, acid, or containing any salt. If this residue is not obtainable, I can take a
bichromate of soda, potash or ammonia, which I separate, and, by the aid of a
reducing agent, such as sugar, flour, or sawdust, and an addition of sulphuric acid,
and produce a chrome alum, which I precipitate in the same manner as the alum
from the batteries.
After having obtained this hydrated sesqui-oxide of chromium (chromic-hydrate) I
combine with it hot sulphuric acid of a specific gravity of 16 to 18 degrees Baume,
which gives me an absolutely pure sulphate of chromium.
I subject this sulphate to the same operation as the alum, the same washing and
decanting, and I have then hydrated sesqui-oxide of chromium (chromic hydrate) in
a perfect condition.
A vat or receptacle is provided of a suitable size, according to the quantity of
eather or skins to be treated, and of a depth exceeding, by two feet, the length of the
uides or skins, which are placed vertically in the vat. I thereupon make a bath of
water, adding sulphuric acid, nitric acid, or any other suitable acid to give it a specific
gravity of 4 degrees Baume, stirring the liquid well and allowing it to stand for
bout three days, for the purpose of allowing it to cool, perfectly. I next add to the
bath perfectly neutral hydrated sesqui-oxide of chromium, (chromic hydrate,) but
while I am not able to state the exact proportions of the solution and the hydrated

page_text: sesqui-oxide (chromic hydrate) I have a very easy test, as the liquid dissolves as much
as its character and affinity will permit and the surplus, exceeding its capacity, will be
deposited upon the bottom of the vat, being heavier than the liquid.
It is essential in preparing a new vat to agitate the solution for about four
consecutive days, so as to keep the hydrated sesqui-oxide of chromium (chromic
hydrate,) suspended during this entire period, and to allow the liquid time to become
fully saturated with the same.
After the new bath has been prepared in this manner, and the surplus of hydrated
sesqui-oxide (chromic bydrate) has had time to settle, I immerse the leather or skins
vertically into the liquid, and allow them to remain therein from 12 to 18. hours,
ccording to the nature of the tanning to which they have been previously subjected.
The hides or skins are then removed by any suitable means, and the liquid is imme-
diately again agitated, so that a quantity of the surplus hydrated sesqui-oxide
(chromic hydrate) at the bottom of the vat will be absorbed by the acid set free.
The organic nature of leather or skins has a great affinity for metallic oxides, which
destroy the combination in my liquid, fill the pores and cells with the hydrated sesqui-
oxide of chromium (chromic hydrate,) and free the acid, which will drop off when the
skins are suspended in space.
In contra-distinction to all other processes heretofore employed for tanning, my
process consists of softening leather and skins, rendering them absolutely flexible and
giving them a fixed color.
After leaving my solution and after all the liquid has run off from the skins, they
are subjected to the action of a solution of warm logwood, which permanently sets the
sesqui-oxide of chromium in said skins. The leather or skins remain for a space of
time, governed by the nature of said leather or skins, and of the tanning which
they have received in said solution, of which there is a surplus supply, for the
purpose of introducing into the pores and cells of their organic matter a sufficient
quantity of sesqui-oxide of chromium which prevents by its presence, the gelatine
therein from combining and keeps them continually soft and flexible.
Under my process of finishing leather, it is rendered much more impervious
than by any of the finishing operations usually practiced, which consist of stuffing
leather and rendering it pliable by means of greasy, oily, and similar matters, since,
by my process, the oxide of chromium is introduced and firmly set in the pores
of the leather, so that it cannot be removed therefrom under atmospheric influences,
and thus an article is produced which is impermeable as long as it lasts.
The manner of operating or practising with my process is as follows :-
The leather after being tanned in any suitable, previously known manner, is first
dipped into a solution containing the sesqui-oxide of chromium (chromic-hydrate) in
solution which is renewed by agitating the surplus of the finely divided sesqui-oxide
of chromium (chromic oxide) the oxide of chromium is then permanently set in the
pores of the leather by treating the latter with a solution of logwood, so as to
render it impermeable to water, and then finally, coloring the leather, fixing its color
and protecting it against the oxidizing effects of the atmosphere. This will complete
one set of skins; then the process is continued in the same vat for fresh sets of skins
by agitating the solution and its surplus of hydrated oxide of chromium (chromic
hydrate,) previous to each fresh treatment of skins, the subsequent steps being
continued, as before mentioned until the sesqui-oxide of chromium (chromic hydrate)
is entirely consumed.
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 as the invention communicated to me is :-
1. The process herein described of treating leather after tanning, for the purpose of
softening, coloring, and fixing the color thereof, the same consisting in subjecting the
leather to a cold solution of sesqui-oxide of chromium (chromic hydrate) then
subjecting it to the action of a bath of logwood, substantially as described.
2. The process herein described of successively restoring the cold solution of

page_text: sesqui-oxide of chromium (chromic hydrate,) by agitating a surplus body thereof at
the bottom of said solution, previous to treating each batch of leather, so that the
cold solution will reabsorb and hold in solution the proper proportion of said chromic
hydrate, substantially as described.
3. As a new article of manufacture, a skin previously tanned with vegetable tanning
matter and impregnated with the oxide of chromium, substantially as described.
4. As a new article of manufacture, a skin previously tanned with vegetable
tanning matter and having its pores impregnated with oxide of chromium and dyed
with a color partly combined with said oxide of chromium as a mordant, substantially
as described.