Year: 1886

page_text: I, WILLIAM RICHARD EARP of Runcorn in the County of Chester, Chemical
Manufacturer and Analyst do hereby declare the nature of this invention to be as
follows:-
This invention has for its object certain improvements in tanning.
First in depilating, which is generally accomplished by liming or other processes
which have a tendency especially when too prolonged to injure the hide, I quicken
the process, and make it far more effectual by adding to the lime vat an alkaline
sulpharsenate sulpharsenite, disulpharsenate disulpharsenite, persulpharsenate or
persulpharsenite, or I form one or more of these salts in the vat by the use of such
chemicals in equivalent quantities, as will form the same, such as by adding to an
alkaline sulphide arsenious or arsenic acid with one third of its weight of sulphur,
and then passing sulphuretted hydrogen through the whole liquor, or preferably
by adding to an alkaline sulphide, a per sulphide of arsenic with one fourth of its
weight of sulphur, and then passing sulphuretted hydrogen through the whole
liquor as before.
Or instead of adding these substances to the lime vat, I steep the hides in an
alkaline solution of one or more of the said sulpharsenical salts.
The depilated hides are now steeped in the tanning solution, but this solution
I first purify by the addition of sulphurous acid either in the gaseous form or
preferably added in solution. The sulphurous acid appears to form sulphites in
the vat which themselves have a beneficial effect with the liberation of tannic acid,
and possibly the reconversion of any gallic acid into tannic acid, and the pre-
cipitation of deleterious colouring matter.
Hides depilated by means of the sulpharsenical salts instead of lime, not having
lime in their pores are very much quicker and more economically acted upon by
the tannic acid than ordinary limed hides and the use of injurious acids to wash
off the lime is avoided, and by the use of sulphurous acid in the liquors from which
it precipitates objectionable matter, the time taken for tanning is thereby much
further shortened. The sulphurous acid, instead of having any detrimental effect
on the pelt, tends the other way and enables a better grain to be got, and also a
better colour.

page_text: Considerable advantages are gained by the use of this process. The loss of
tannic acid, except what is taken up by the hide will be found to be very slight, if
any objectionable matter is precipitated from the liquors, a better colour is
obtained, and the time employed in tanning will be greatly reduced. I estimate
the increase of weight in the leather will be about 4 lbs. in a 70 lb. hide, and a
leather with a better grain and firmer will be produced, without any appearance of
what is known as "Sago" fermentation, and consequent loss is avoided, the tannic
acid taken up by the lime or other base is liberated, and becomes available to be
taken up by the hide, and the tendency is to form tannic acid from gallic acid
rather than the contrary.

page_text: Improvements in the Manufacture of Leather.
I, WILLIAM RICHARD EARP of Runcorn in the County of Chester, Chemical
Manufacturer and Analyst, 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 :-
I depilate the hides by steeping them in an alkaline solution of a sulpharsenate,
sulpharsenite, disulpharsenate or disulpharsenite or a mixture of these, I prefer the
soda salts.
The quantities I prefer are by weight from five to eight parts of the sulpharsenical
salt to 100 of water. In place of forming the salt first, and adding it to the vat,
I may form one or more of these salts in the vat itself, as by adding an alkaline
sulphide and arsenious or arsenic acid in equivalent proportions and saturating
with sulphuretted hydrogen.
The hides depilated by this means are free from lime in their pores, they are
therefore much more speedily and economically acted upon by the tannic acid of
the tan pit. To however still further increase the activity of the tan pit, and at
the same time utilize all the tannic acid in the materials, I add sulphurous acid,
either in the gaseous form or in solution to the tan liquor, this causes a pre-
cipitation of colouring matter, liberates the combined tannic acid, appears even to
have some action in converting gallic acid into tannic, and lastly forms sulphites
in the liquor which are of great assistance to the whole operation of tanning. The
exact quantity of sulphurous acid required varies with the quality and quantity of
tan liquor, but for an average tan pit of say 7 × 5 × 5 feet deep I put in a gallon
of 4 Twaddle, where divi is used more will be required. It is obvious that my
improvements can in whole or in part be added to the present process with
advantage, thus the sulpharsenical salt or salts can be added to the lime vat
greatly improving the same, and sulphurous acid in lesser quantity than necessary
to precipitate all the precipitable colouring matter, or liberate all the tannic acid
can be added to almost any tan pit with advantage. In conclusion, I am well
aware that weak acid baths have been used to extract the lime from the pores of
the leather after liming, that sulphuric acid and hydrochloric acid have been pro-
posed for additions to the tan pits, to liberate additional quantities of tannic acid,
but they act very deleteriously on the leather, and I make no claim for their use,
restricting myself to sulphurous acid or such compounds as bisulphites which easily
give off sulphurous acid in the vat.
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:-
1. The improvements in the process of manufacturing leather which consist in
depilating the skins in a solution of a sulpharsenical salt, such as described, and
then tanning them in an ordinary tanning solution or solutions to which sulphurous
acid has been added.

page_text: 2. The improvement in the depilating of skins, which consists in treating them
with an alkaline solution of one or more of the sulpharsenical salts above set forth.
3. The improvement in the depilating of skins, which consists in forming a
sulpharsenical salt, such as described in an alkaline depilating vat and exposing
the skins therein.
4. The addition to a lime depilating vat of a solution of one or more of the
sulpharsenic salts herein before enumerated.
5. The addition to a lime depilating vat of such substances as by their mutual
decomposition or combination form one or more of the sulpharsenical salts herein-
before described.
6. The improvement in the process of tanning which consists in adding to one
or more of the tanning vats, sulphurous acid or bisulphite and treating the skins
therewith.
7. The improvement in the process of tanning which consists in exposing the
depilated skins to sulphurous acid and to ordinary tanning materials.
8. The process of precipitating the colouring matter of tanning solutions without
injury to the same for tanning purposes, which consists in adding sulphurous acid,
substantially as described.
A
T
1000