Improvements in Processes of Tanning.
Year: 1897

page_text: Date of Application, 15th May, 1897-Accepted 24th July, 1897
Improvements in Processes of Tanning.
I, CHARLES SUMNER DOLLEY, of 683 Bourse Building, Philadelphia, in the County
of Philadelphia, and State of Pennsylvania, United States of America, Gentleman,
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:-
This invention relates to improvements in tanning hides or skins, and the objects
of the invention are to provide a single step tanning process which is simple,
inexpensive, efficient and rapid, and to produce a soft, tough and pliable leather
sound in texture and which is free from discolouration and harmful foreign matters,
and is well adapted to be finished and coloured by any of the ordinary finishing and
colouring methods and agents.
My invention consists essentially in subjecting the hide or skin to be tanned to
the action of formicaldehyde (CHO) in such manner and proportion and for such
time that the hide or skin under treatment shall be thoroughly permeated by the
formicaldehyde which I have discovered will, under proper conditions, form an
insoluble compound with the gelatinous constituents of the hide or skin, and at the
same time effect those other chemical and physical changes essential to the
conversion of a raw hide or skin into leather.
In carrying out my process I take a hide or skin which has been prepared for
tanning by one of the commonly employed modes, according to the particular
character of the hide or skin under treatment, and I subject said prepared hide or
skin to the action of formic-aldehyde either in its natural gaseous condition, or in
aqueous solution, the degree of concentration of the gas or the strength of the
solution and the time of treatment, varying, of course, with the character and
thickness of the hide or skin to be tanned. If the formicaldehyde be employed in the
form of an aqueous solution, I have found the following an advantageous method to
pursue for the conversion of ordinary goat skins into morocco leather: 1 begin the
treatment with, preferably, say a three per cent. solution of the formicaldehyde, and
treat the skins in this solution in a closed drum for say ten minutes, adding
formicaldehyde to the solution at intervals of say ten minutes until at the end of an
hour or thereabouts the solution has been brought up to a strength of ten per cent.,
and the hides have thus in the interval been subjected to the continuous action of a
tannage solution of gradually increasing strength. I have found in practice that
ordinary goat skins treated as above described, may be thoroughly tanned in a
period of an hour or thereabouts.
The hides or skins should be subjected to the ordinary tests known to tanners
from time to time during the process, and should be allowed to remain and to be
agitated or revolved in the druin until said tests applied to the thickest portions of
the thickest hides or skins under treatment, indicate to a person skilled in the art,
thorough permeation, and through and through conversion of the hide into leather,
the hide or skin having lost the tripy translucent appearance and peculiar feel of a
raw hide, and become opaque and colourless and leathery to the touch through and
through.

page_text: If the formicaldehyde be used in a gaseous state I suspend the hides or skins to
be tanned in a chamber capable of being hermetically closed, and connected with
any suitable form of apparatus for generating formicaldehyde gas. The skins
being suspended within this chamber and the door closed the formic aldehyde gas
is introduced into the chamber, and this is continued and the hides or skins
subjected to the action of the gases, or mixed gas and vapour, until the ordinary
tests indicate to a person skilled in the art, that the hides or skins have been
thoroughly permeated by the tanning agent and that the conversion of the hide or
skin into leather is complete.
If the formicaldehyde be employed in a gaseous state I find that ordinary
prepared goat skins suspended in a tight chamber, having a capacity of say 2000
cubic feet may be thoroughly tanned by the action of the quantity of formicaldehyde
gas generated by the ordinary process from one litre of wood alcohol.
The formicaldehyde may also be employed in the gaseous state by the vaporization
of an aqueous or alcoholic solution, and I find that if it be used in this manner, it is
desirable to add a proportion of chloride of calcium to the formicaldehyde solution,
polymerization of the formicaldehyde being in this manner largely prevented. For
this purpose 200 parts of chloride of calcium for each 1500 parts of formicaldehyde
solution suffices. In case the gas is employed in connection with aqueous vapor, it
should of course be understood that live or heated steam is not employed but rather,
a cool vapor or moisture charged atmosphere.
It sometimes occurs that a batch of skins which, by reason of their unusual
thickness or from other cause, may require a strength of the tanning solution
differing somewhat from that employed in tanning ordinary hides or skins and it is
at once evident that in such case the tanner may readily by selecting a fair specimen
of the batch of skins to be tanned, and using the same as a test for the strength
of the tannage solution required, more readily determine the strength of the
solution which may be required in tanning such hides or skins.
The product of the above described process is a tanned hide or skin or leather,
consisting essentially of the combination of formicaldehyde with the collagen and
other gelatinous constituents of the skin or hide, and which is distinguishable from
any ordinary leather known to me by its entire freedom from discolouration, or from
any foreign matters such as mineral or organic salts or acids, while at the same time
it is soft, tough and pliable, and yields itself readily to any of the ordinary finishing
methods of finishing currying and coloring.
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is
1. As a new article of manufacture, a tanned hide or skin consisting essentially
of a combination of formicaldehyde with the collagen and other gelatinous
constituents of the said skin or hide substantially as herein set forth.
2. The hereindescribed process of tanning, that is to say, subjecting the hide or
skin to be tanned to the action of formicaldehyde (CH,O) as herein set forth.
3. The process hereindescribed of tanning, that is to say, subjecting the hide or
skin to be tanned to the action of formicaldehyde (CH₂O) commingled with aqueous
vapor, substantially as herein set forth.
4. The process of tanning which consists in subjecting the hide or skin to be
tanned to the action of forinicaldehyde (CH2O) employed in aqueous or alcoholic
solution, substantially as set forth.
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