Improvements in Tanning and Currying Hides and Skins.
Year: 1886

page_text: Improvements in Tanning and Currying Hides and Skins.
I, WILLIAM PHILLIPS THOMPSON, Fel. Inst. P.A. of the Agency for Foreign
Patent Solicitors, 6 Lord Street, Liverpool, in the County of Lancaster, and
323 High Holborn, in the County of Middlesex, Civil Engineer, do hereby declare
the nature of this invention (a communication from abroad by John W. Fries of
Salem, County of Forsyth, State of North Carolina, United States of America,
Manufacturer) and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement :-
This invention consists in a novel method or process of tanning, hereinafter more
fully set forth, the invention relating to those operations performed subsequent to
the liming and unhairing of the hides.
It has long been known that copperas (sulphate of iron) would tan hides but
the quality of leather produced by its use has not been such as to cause its general
adoption.
This invention is designed to secure a better quality of leather than has hitherto
been possible through the use of copperas, and is carried into effect as follows:
The hides previously limed and unhaired in the ordinary way for tanning with
oak bark or by sweating or by the aid of sulphide of sodium, or other process are
placed in a bath of carbonate of iron, where they should be suspended in a rocker
handler" for two days, more or less, and agitated from time to time.
.
"
For this bath the inventor employs carbonate of protoxide of iron, dissolved in
water, and it is not material from what source or agents this is obtained nor is it
important to observe closely any stated quantity of chemicals used to a given
quantity of water,
The water even when saturated with carbonic acid, will dissolve but a limited
quantity of the carbonate, but for this reason there should always be an ample
supply of undissolved sulphate of iron in the bottom of the tank.
If carbonated well water is used which contains usually a considerable amount
of carbonic acid in solution naturally a good working proportion of chemicals
would be:

page_text: Copperas
3 lbs. }
Bicarbonate of Soda 2 lbs, per cubic foot of water.
To this liquid may be added sugar, in the proportion of, say one half pound of
sugar to each pound of copperas, for the purpose of preventing the protoxide of
iron from passing into the sesquioxide, but the use of saccharine matter is not
essential to the process.
In the continual use of the same vat, with the addition of copperas and soda
from time to time, the liquor soon becomes super-saturated with sulphate of soda,
and it therefore becomes desirable to allow the liquor to settle from time to time,
and to draw off the clear portion which contains the sulphate of soda in solution,
saving the carbonate of iron precipitate at the bottom of the vat and filling up with
clear water.
To this is added enough sulphuric acid to cause it to effervesce, and it should be
kept near the point of effervescence by further additions of sulphuric acid every
day or two, more or less, but care should be taken not to add the acid in such
quantity nor to continue the effervescing action so long as to drive off the carbonic
acid of the carbonate.
The liquor should be kept constantly saturated with carbonic acid.
After the hides have been fully acted on by this carbonate solution, which
requires only two or three days, they are transferred to another liquor consisting
of copperas and common salt dissolved in water.
It is not material that these salts be in very exact and definite proportions to
each other or to the quantity of water in which they are dissolved, but in practice
no disadvantage is found in employing a strong solution, and as there is no waste
or deterioration it is advisable to make the solution strong to ensure efficient
action, say-
Copperas 25 to 40 lbs.
Common Salt 15 to 25 lbs.
}
per cubic foot of water.
In this, as in the first liquor, it is desirable to have the hides suspended as in a
rocker handler, and agitated from time to time so that the liquor shall have free
access to and come into contact with all parts of the hide.
Two or three days in this liquor are sufficient to complete the tanning.
When taken from this liquor the hides do not have the appearance of leather
tanned by ordinary processes, but on being hung up to dry, the iron throughout
the body of the hide becomes thoroughly oxidized, and the leather becomes firm,
fibrous, and of a yellowish brown color.
The currying of this leather may be similar to that of bark tanned leather in a
general way, but must be varied somewhat as to details. Thus ordinary tanners'
fish oil is not readily absorbed by leather tanned as above, but tends to make it
hard and dark, and glazes its surface, giving the appearance of a coat of varnish.
A mixture of beef tallow with paraffine oil, answers well, and hogs' lard and
cotton seed oil also give good results.
Various experiments have shewn however that castor oil and alcohol mixed
together give results superior to any other preparation or substances known to the
inventor for currying and finishing hides treated in the manner above set forth.
The peculiar advantage of the castor oil and alcohol preparation consists in the
fact that it will penetrate the leather while the latter is drying, whereas with the
exception of glycerine, other substances have been found incapable of so doing.
Glycerine is so hygroscopic that in some conditions of the atmosphere leather
treated with it becomes quite wet.
:
Without this it is found necessary therefore to dry the hides after taking them
from the copperas liquor or solution, and to apply the oil thereto after the
drying is completed, In many cases the leather in drying becomes harsh and
brittle and no subsequent treatment will restore its pliability; but by employing

page_text: the castor oil and alcohol to the hides as they are taken from the copperas solution
the difficulties previously encountered are entirely obviated.
The proportions of alcohol and castor oil will depend somewhat on the purpose
for which the leather is designed: fifty per cent of each ingredient is a good
proportion in most cases.
Having now particularly described and ascertained the nature of the said
invention, and in what manner the same is to be performed, as communicated to
me by my foreign correspondent, I declare that what I claim is :-
1. The method of tanning leather, which consists in subjecting the hide to the
action of a bath containing carbonate of iron.
2. The process of tanning or finishing hides for the production of leather, which
consists first in liming and unhairing the hides, then subjecting them to a bath or
solution containing carbonate of iron; next subjecting them to a solution of
copperas and common salt dissolved in water; and finally treating them with
cotton-seed oil or other oil or fatty substance capable of readily entering the
pores of the leather.
3. In a tanning and finishing process, the steps which consist in first liming and
unhairing the hides in any usual or convenient manner; second, subjecting the
hides to a bath of water containing carbonate of iron in solution, and third,
removing the hides from the carbonate solution and subjecting them to the action
of a bath of copperas and common salt dissolved in water, substantially as set
forth.
4. The herein described process of tanning and finishing hides, consisting in first
liming and unhairing the hides in any usual or convenient manner; second
subjecting the hides to a bath of water containing carbonate of iron in solution;
third, removing, them from the carbonate solution and subjecting them to the
action of a bath of copperas and common salt dissolved in water; fourth, bringing
them under the action of the atmosphere whereby the ferrous oxide contained in
the pores of the hide is changed to a ferric oxide, and fifth, treating the leather
thus formed with cotton seed oil or other fatty substance substantially as and for
the purpose set forth.
5. The step in the treatment of hides which have been previously treated in
solutions containing respectively carbonate of iron, and copperas and common salt
dissolved in water, which consists in applying to them a mixture of castor oil and
alcohol.
6. The method of treating leather after treatment in solutions containing
respectively carbonate of iron, and copperas and salt; which consists in applying
to said hides while they are wet with the last solution, a mixture of castor oil and
alcohol.