IMPROVEMENTS IN TANNING HIDES AND SKINS
Year: 1884

page_text: I, ALEXANDER MELVILLE CLARK, of the firm of A. M. and Wm. Clark, of
53, Chancery Lane, in the County of Middlesex, Fellow of the Institute of Patent
Agents, do hereby declare the nature of the said Invention for "IMPROVEMENTS
IN TANNING HIDES AND SKINS" 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 method of obtaining from spent bark and other
tanning material a liquid by which hides and skins can be prepared for the
operation of tanning thereby utilizing an otherwise worthless material and at the
same time improving the hides so treated whilst the tan liquors treated in the
same way are made capable of tanning a much larger amount of hide than
could be tanned with the same quantity and strength of tan liquor without the
use of the auxiliary liquid whereby a great saving in the tanning material proper is
effected.
In order to produce the aforementioned desirable results I cause pure freshly
made sulphurous acid to pass into and through the "leaches" containing the
spent "bark" or used-up tanning material and from thence into the vat, bath or
receptacle set apart for the purpose of tanning and coloring the green hides
or skins.
The same liquor either after passing through the spent bark or used-up tanning
material, or without passing through the same, is mixed with the freshly
prepared tan liquor in order to render its capacity for tanning much greater.
Experience has proved that a saving of one fourth of the tanning material proper
may be made by the use of this adjunct (sulphurous acid) and not only is this
great saving in the tanning material effected, but a very considerable amount of
time is saved also, the operation of tanning being expedited nearly one fourth.
Moreover the hides or skins so treated are softer, plumper and heavier than they
would have been if they had not been subjected to the treatment abovementioned,
namely, the use of pure sulphurous acid in the tan liquors in the manner above
described.
In order that any person may use the aforementioned auxiliary, I would state
that for "coloring" sole leather I cause the hides to be "colored" in a vat or bath
containing one half liquor that has passed through the spent bark or used-up
tanning material as aforementioned, the remainder being made up with weak tai

page_text: liquor of about from 2° to 4° Twaddle whilst in the after operations the quantity
is increased one twelfth for overy 10° of volumetric density.
Thus one foot of tan liquor at 10° requires the addition of one inch of sulphurous
acid in summer. If the water be hard or contain lime or organic deposit more
sulphurous acid must be used.
For lighter stock the amount of acid must be proportionately less according to
thoir age.
In practico I find that the best way to prepare the sulphurous acid or hydrogen
sulphite is to produce and hydrate it under normal conditions of temperature and
pressure.
I am aware that sulphates and sulphides have been used in tanning operations.
Having now particularly described and ascertained the nature of my said
Invention and in what manner the same is to be performed, I declare that what
I claim is:-
The employment of sulphurous acid or hydrogen sulphite in tanning hides and
skins, for the purposes and in the manner herein set forth.