Improvements in and relating to Tanning Hides and Skins.
Year: 1892

page_text: This Print is in accordance with the Original Specification as it stands after
Amendment (under Section 18 of the Patents, &c. Act, 1883) as allowed
by the decision of the Comptroller General of the 12th day of November 1898..
Date of Application, 4th May, 1892-Accepted, 4th June, 1892
[A communication from abroad by DURIO BROTHERS, of Turin, in the Kingdom
of Italy, Tanners.]
Improvements in and relating to Tanning Hides and Skins.
I, HENRY HARRIS LAKE, of the Firm of Haseltine, Lake & Co., Patent Agents,
45, Southampton Buildings, in the County of Middlesex, 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:-
It is well known that leather suitable for numerous industrial purposes are
obtained by tanning hides or skins treated after a certain preparation with
different reagents having a base of tannin, and persons experienced in this art
know perfectly well how long this operation takes which, up to a few years
ago, was carried on exclusively in tubs or pits where the hides or skins remained
for months in contact with solutions of tannin at first very weak and then a little
stronger. It is true that with the object of hastening this operation and above
all of diminishing the enormous capital required by this industry owing to its
immobilisation for so long a time, more rapid processes have been adopted for
some time, founded either upon a species of working or drumming or mechanical
fulling in receptacles which may be either closed or open, in order to reinforce
the action of the solutions of tannin on the hides or skins by constantly renewed
contact, or upon the addition of various substances (different acids, turpentine
and other materials) to the solutions of tannin to render the action more ener-
gètic, or lastly upon the passing of an electric current through the material under
treatment in order to render it more suitable for undergoing the action of the
tannin.
By the drumming or fulling and especially by electricity, when used conjointly
with the drumming, the duration of the operation has already been considerably
shortened; but the drumming or fulling alone is still far from giving the desired
results, and electricity necessitates such great cost of installation and working
that the economic advantage of the shortened operation is lost to a great extent.
As to the addition of the substances mentioned or other similar substances, trials
have shown its perfect uselessness.
On the other hand the process which forms the subject of the present invention,
while profiting by the drumming or mechanical fulling (which as above stated has
heretofore not given sufficiently satisfactory results with regard to rapidity and,
production), enables a greater production to be obtained and the tanning to be
effected with such promptitude as has not heretofore been suspected. Owing on
the one hand to the theories taught, and on the other hand to the fear of burning
or otherwise damaging the hides or skins, tanners have up to the present time

page_text: used altogether too weak solutions of tannin, whatever may be the system
employed, and they subdivide, as it were, the operation into several consecutive
stages, either by introducing successively and always for a long time the material
to be treated into several receptacles wherein it comes in contact with solutions
that are each time weaker, or they withdraw from time to time the solution
which has been used in order to replace it by another which is slightly more
concentrated. But they commence with solutions of tannin of about I degree
or at most 2 degrees Baumé in order to come gradually to the maximum of from
3 degrees to about 4 degrees Baumé.
י
The present improved process is based upon the simultaneous employment of
violent drumming or fulling in à receptacle of suitable form and of solutions
of tannin having a very high degree of concentration, incomparably above those
the use of which has heretofore been authorized by theory and custom.
The receptacle may be an ordinary cask or barrel mounted upon its axis, or a
parallelopipedic case mounted at two diagonally opposite corners (their rotation
producing the fulling); or perhaps a fuller or other apparatus which by its move-
ment is capable of mixing and working energetically the material of the hides or
skins to be treated. I prefer however, as better answering the requirements of
the operation, a cask or barrel adapted to rotate upon its axis and which is large
enough but not too large, and practice has shown that it is preferable to give
the same on the average an inner diameter and an inner length of six and a half
feet each, these dimensions being sufficient for treating about 10 to 12 cwts. of
hides and even more. But it will be readily understood that I do not limit myself
to these dimensions which must of course be greatly varied according to the
number of hides or skins to be treated.
Into the cask barrel or other apparatus is poured a solution of tannin of about
6 degrees Baumé, so that its upper level will be about 3/4 inch below the rotary
axis. Any good tannic extract is likewise suitable, and also any material
containing tannin in sufficient quantity for giving the solution to be employed
the desired degree of concentration. It is not absolutely necessary to add any other
substance or reagent (such as sulphuric or other acid, turpentine and the like),
for the prompt action upon the hides or skins is produced in the present process
solely by tannin of a high degree of concentration. These other materials are
considered inert, and no importance is attached to them in connection with this
process, which is carried out irrespective of the presence or absence of such
materials in the solution employed. To ascertain whether the tannie extracts of
commerce might contain acids or other substances, to which the shortening of the
tanning might be attributed, a concentrated extract of pure tannin has been pre-
pared in the cold state from chestnut wood. A trial has demonstrated a greater
reduction in the duration of the operation and at the same time a greater yield
in the weight of the product treated with this extract of really pure tannin.
I introduce into the cask or barrel a suitable number of hides or skins which
need not undergo any special preliminary preparation, except the ordinary
unhairing, fleshing and puring, known by the name of river work; the cask or
barrel is closed and it is then rotated at a velocity which may be varied, but I
use as the most suitable velocity about 10 revolutions per minute.
The operation takes place alone without any necessity for either heat or cold,
an increase of pressure, the production of a vacuum, or the passage of electric
currents, so that these various physical facts are here considered useless and not
prejudicial to the present process, which is entirely independent as regards
their co-operation and their non-intervention in the operation. When the opera-
tion commences the absorption of the tannin by the hides or skins is very rapid
at first and then diminishes naturally. From time to time the movement is
stopped for taking small proofs of the liquid, which is brought back according
to requirement not only to the initial density but to a slightly higher density by
the addition each time of a suitable quantity of extract of concentrated tannin.
In this manner, after the complete tanning of the first number of hides which

page_text: are removed from the cask or barrel, the solution is quite ready for the next
operation. It will however be expedient to filter it after five or six operations
for freeing it from the residues.
As will be seen, the operation is effected in a single receptacle without changing
either the hides or skins or the liquid from one receptacle to another, and it is
continuous (excepting the slight interruptions in the movement for testing and
correcting the solution), in order to accelerate the work, but if any unexpected
interruption should occur it would have no other deleterious effect upon the opera-
tion than that of prolonging it a time equal to its own duration.
This operation of tanning effected according to the improved process naturally
requires a variable time by reason of the quality and nature of the hides or skins.
From 2 to 4 hours are sufficient for small hides or skins such as for example those
of sheep and the like, and from 20 to 30 hours are not exceeded for the heavy and
very thick bull or ox hides, with intermediate durations for other hides such as
calf, cow and similar hides. In the experiments made it has been ascertained
that with a slight increase in the duration of the operation the hides or skins
may be attacked with weaker solutions, for example from 3 to 4 degrees Baumé,
strengthening them little by little. But it has always been found that not only
is it not at all needful to commence with a solution having a low degree of con-
centration but that it will be much better to commence at least with from G
to 6 degrees and even with 8 degrees and more; and that increasingly satis-
factory results are always obtained both as regards rapidity of work and beauty
of the product, which does not suffer in any way from this employment of reagents
which are of such great strength.
In like manner when the duration of the operation is varied I may vary the
degree of tannic concentration of the reagents. The tanner who is experienced
in his art will readily be able to select from the various tannic extracts of com-
merce (mixing them if necessary) those will impart to the leather the shades
that suit him best for his market.
I may observe that it is not necessary in the present process to change (during
the operation) either the receptacle the hides or skins, or the liquid, and I need
not limit myself to the exact quantity of liquid above mentioned relatively to
the size of the receptacle. Evidently the operation will succeed with a smaller
quantity of tannic liquor in the same cask or barrel for example with only one-
quarter of the total volume, the sole condition being to limit also in proportion
the hides or skins to be treated. A small number of hides or skins may also
be treated in a large volume of liquid.
It should be observed that at the end of the various durations of the opera-
tion the latter is terminated for nothing is gained by continuing it, as the con-
secutive proofs taken show that the hides or skins absorb no more tannin. It is
true that they do not suffer from it either, at most the grain of the same becomes
perhaps a little harder, so that every greater duration given either knowingly
or capriciously to the operation, not only would not be an improvement but on
the contrary. retrogression.
At this point the hides or skins removed from the cask or barrel are ready to
be subjected to the carrying and finishing operations for the various commercial
uses. However it should be noted that the hides or skins (even after washings
in slightly tannic or even pure water) present sometimes a slight defect in appear-
ance (once finished), especially if they have been dried rapidly either by exposure
to the sun or by strong heat; they darken a little upon the surface, chiefly at the
edges, by reason of the deposits left by the drying thereon of the very strong liquid
in which they have been immersed. For obviating this inconvenience it is suffi-
cient to place them (such as they are when they come from the tanning cask or
barrel) in another cask or barrel containing water with tanning liquor which
washes away the aforesaid deposits. They are fulled therein for from two to
four hours, after which they are removed washed and spread out to dry, as is
ordinarily the case with hides or skins taken from the pits. This operation

page_text: which has for its object to prepare the leather for a better finish gives more yield
and a finer appearance besides obviating the above-mentioned inconvenience.
It is scarcely necessary to state that the products thus obtained not only rival
in beauty and quality the leathers tanned by the best processes heretofore known,
but even surpass them. In fact by this improved process driving belts have
been made which possess a greater strength than that obtained by any of the
known systems.
Having now particularly described and ascertained the nature of this 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: --
First. In the tanning of hides and skins the improved process characterized by
violent fulling and the employment of a tannic solution concentrated to a much
higher degree than those heretofore used, preferably 8 degrees Baumé but which
may vary from about 4 to 20 degrees Baumé, the concentration being either main-
tained uniform or (especially in the case of the less concentrated solutions)
increased so that at the end of one operation it will be suitable for the next, the
entire operation being preferably effected in a single receptacle, such as a rotating
cask or barrel, without any special preparation of the hides, or skins, with or
without the addition of reagents to the tannic solution, with or without the aid
of any special accessory device, with or without the finishing operation, substan-
tially as and for the purposes herein described.
Second. As a new article of manufacture, the product obtained by the tanning
process herein before described.
Dated this 4th day of May 1892.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C.,
Agents for the Applicant.