Improved Process of Tanning with Mineral Agents.
Year: 1895

page_text: Date of Application, 16th May, 1895-Accepted, 22nd June, 1895
COMPLETE SPECIFICATION.
Improved Process of Tanning with Mineral Agents.
We, MAX JULIUS VÖLCKER, Leather Manufacturer and MAX WILHELM
GEORG BERGMANN, Apothecary, both of Eisenberg, Duchy of Saxony-Altenburg
in the Empire of Germany, do hereby declare the nature of our said 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 a process of tanning with the aid of mineral agents
alone, its object being to treat the skins or hides of animals, without employing
any vegetable tannins, in such manner that a leather is produced which is elastic
and which, after being put, for instance, in hot water, remains elastic, strong and,
at the same time, smooth grained; a leather possessing such qualities is particularly
desirable for boot-uppers.
According to this process the hides or skins, after having been unhaired and
fleshed in the usual manner, are preferably put into a rotating tumbler-drum of
known construction and therein subjected for to 2 hours-according to the kind
of hide to the action of ammoniacal vapors. Such vapors thoroughly remove
any calcareous and sebaceous matter still adhering to the hides and thus bring
the latter into a condition for readily taking the tanning agents. At the same
time the vapors so act on the albumen, gelatine and other substances in the hide
especially on the grain-side of same, that the finished leather is rendered very
elastic, strong and at the same time soft and flexible to the touch, such qualities
being specially requisite for upper-leathers.
The
The hides thus treated are then preferably subjected to a preliminary tanning
in a tumbler drum containing a mineral solution composed of about 10% alum
and about 5% chloride of sodium and preferably maintained at a temperature
of 25° to 35° Centigrade, for effecting a more rapid and uniform treatment.
treatment with such solution lasts 3-12 hours, according to the thickness and
nature of the hide. The final tanning is effected with a 5% solution of chromic
acid or chromic salts, likewise heated, and occupies 2-4 hours.
The concen-
tration of such solution must be maintained uniform during this time.
The hides thus tanned are now passed through water, or slightly rinsed, in
order to remove the chromic acid adhering to surface of the hides and, for fixing
the tanning agents in the hide, same are finally treated with sulphide of hydrogen,
which decomposes the chromic salts and forms insoluble chromic oxide. This
treatment with sulphide of hydrogen may at the same time be utilized for dyeing
the leather; in that case it is necessary to employ a bath in which sulphide of
hydrogen (by virtue of its known reaction) precipitates a substance which serves
as the coloring matter.
The afore-described process is preferably carried out in an apparatus arranged
in series or as a battery, so that the hides may be subjected to the several
treatments in their due and unbroken succession.
The leather tanned and, if desired, dyed in the manner above-described, is now
finished in the usual way.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed I declare that what i
claim is :-
Process of tanning with mineral agents, consisting in first treating the cleaned
hides with ammoniacal vapors, subiecting same to a preliminary tanning with a

page_text: solution of alum and common salt and then with a solution of chromic acid or
chromic salts maintained at a uniform concentration and, finally, treating such
hides with sulphide of hydrogen for fixing the tanning, substantially as described.
Dated this 16th day of May 1895.
:
W. P. THOMPSON & Co.,
31, High Holborn, London, W.C., Patent Agents for the Applicants.