Improved Process for Tanning and Treating Hides and Skins.
Year: 1899

page_text: Date of Application, 17th Mar., 1899
Complete Specification Left, 16th Dec., 1899-Accepted, 10th Feb., 1900
PROVISIONAL SPECIFICATION.
Improved Process for Tanning and Treating Hides and Skins.
I, RAYMOND COMBRET, of 18, Rue Mogador, Paris, France, Doctor of Medicine, do
hereby declare the nature of this invention to be as follows:-
very weak solutions of formic aldehyde containing
My invention relates to an improved process for tanning and treating hides and
skins of all kinds which consists in treating them on issuing from the rincing or
soaking process with
systematically determined quantities of free acids, which may however be varied
according to the nature of the hides treated, such treatment being effected in suitable
vessels either at the temperature of the surrounding atmosphere, or preferably at a
moderated temperature in closed vessels to which motion is imparted by mechanical
means.
My improved process for utilising the essential and direct tanning action of formic
aldehyde differs entirely from the experiments which have hitherto been made with
such aldehyde in the ordinary tanning processes; it also differs from the various
trials that have been made for utilising such aldehyde directly as the principal tanning
agent.
In carrying out my improved process the general rule is observed of never, during the
course of the tanning process and in particular at the commencement, putting fresh
swelled hides or skins in direct contact with liquors which only contain formic aldehyde
in solution, no matter how weak it being absolutely necessary in all cases that there
shall be simultaneously present, in the liquor up to the end of the process a sufficient
quantity of free acids (whether these are produced from the fermentation of old
liquors, or are freshly added), because the methodical combination of these two
actions of the formic aldehyde and of the free acids alone enables advantageous
practical results to be obtained.
In carrying out my improved process the same precautions have to be taken as in
the ordinary tanning process, that is to say, the first liquors must be comparatively
weak as to the tanning agent and strong as to the acid constituents, and in the
subsequent treatment the tanning agents should be gradually increased in strength
while the acid constituents are decreased.
In observing this rule with my improved process, it must be taken into account
that the tanning action of the formic aldehyde is very much more rapid than that of
all known tanning agents and that consequently it is necessary to modify the
proportions of the several ingredients accordingly.
For this purpose there inay be used any kinds of acid but I prefer to employ acetic
acid, which is miscible in all proportions with formic aldehyde, and is very efficaceous
for effecting and maintaining the swelling of the hides and skins, although its action
is gentle and easily regulated.
This acid can be readily produced by the lixiviation of exhausted tanning powders
in which glucoses may if necessary have been fermented; it may also be obtained by
treating the crude acetates derived from the pyrogenous distillation of wood or other
vegetable matter, whereby at the same time the quantities of formic aldehyde
necessary for my process are obtained by means of methylic alcohol, so that the new
process is thus rendered very economical,

page_text: The acetic acid can, if necessary, be replaced by other acids, in particular lactic
acid, which exists simultaneously therewith in the acid liquors of tanneries, but in
this case it is necessary to use from 20 to 25 p.c. more.
sulphuric acid is used, from 20 to 25 p.c. less must be used.
employed but in about double the quantity of the lactic acid.
If on the other hand
Oxalic acid can also be
The quantity of acid (commercial acetic acid of 40° Bé.) employed at the com-
mencement can be much greater than the formic aldehyde (ordinary commercial
solutions), for instance in the proportion of about ten to one; but in that case the
hides must be rapidly transferred to liquors stronger in formic aldehyde, or this
ingredient must be gradually strengthened in the same liquor.
Towards the end of the tanning process, on the other hand, the aldehyde can be
present in greater proportion than the acid, but this excess of acid must be in pro-
portion to the excess of acid at starting.
.A good practical result will be obtained for example if at the commencement the
well prepared hides are treated with a liquor containing from three to five times as
much acid as aldehyde, and subsequently solutions are employed either in the same
vat or in different ones, having the successive proportions of 4 of acid to 2 of
aldehyde, 4 3, and 4: 4.
:
The process may either be stopped there, or the successive
variation of the proportion may be continued until there is from 4 to 5 times as much
aldehyde as acid. As a rule this latter treatment would be limited to large hides,
and the process would be carried on rapidly, particularly towards the end.
As to the absolute quantity of formic aldehyde necessary for the complete
conversion of the hides into leather, this may be very weak at starting,
th part
1000
of the solution for example, and never exceeding
5
25
1,000
1
th even for large hides. A
begining may be made with or of the solution, finishing with
15
1000.
2.5
1000 1000
10
1000
or
The liquor used as solvent may for example be the acid juices of spent tan; in
this case the acidity of the liquor would be increased if necessary until the above named
proportions are obtained.
In practically carrying out my invention the following proportions may be used
with advantage.
1. FOR LARGE STRONG HIDES.
To 1,000 litres of water, with 10 to 15 litres of acid, there are taken from 1 to 1.5
litres of formic aldehyde at starting, then the proportions are successively increased
to,,.... until the inverse of the proportion at starting is reached, that is to
say, 1 to 1.5 litre of acid to from 10 to 15 litres of aldehyde.
These relative differences would be about the highest; in other cases the propor-
tion of acid may be diminished only to one half or one quarter of the original dose,
while still farther increasing the dose of aldehyde at the finish; for example
.15 acid 2.5 aldehyde
10 acid
at starting, then successively 5 aldehyde' 10 aldehyde’
1,000
5 acid
to
1,000
&c.
15 aldehyde
10 acid
With 1,000 litres of water may be used with advantage at starting 2.5 litres formic
aldehyde and 10 litres of acid, then, and if necessary 18 &c.

page_text: respectively 2.5, 5, 10 or if necessary 15 litres of formic aldehyde, the process being
carried on rapidly, more particularly towards the end.
The treatment can be carried on either at the atmospheric temperature and in any
kind of moveable or fixed receptacles, but it is very advantageous to employ closed
and mechanically moved vessels, such as revolving drums and the like working at
moderate temperatures.
The process may be completed in a few hours for small skins, and in two or
three days for the largest hides.
Skins with the wool or feathers and the like may be effectually and rapidly
treated in a single bath of equal parts of formic aldehyde and of acid or a little
more of the latter.
If it be desired to obtain white leathers, the process is carried out with pure water,
but the hides may be dyed more or less either before, during or after the
tanning, by means of coloured extracts for example of oak, chestnut, fir &c., or
they may be dyed various colours, such as yellow, blue, red &c. or have a
metallic lustre imparted to them or be otherwise treated in any known manner
for rendering them waterproof. They may also be supplementally treated with
ordinary tanning agents or extracts, but such subsequent treatment would not be
with a view to perfect the tanning process above described, as this leaves nothing to
be desired as regards the perfect tanning of the hides or skins, and the subsequent
treatment would only be with a view to modifying their appearance or texture, such
as for imparting to them the appearance of ordinary tanned leather.
Dated this 17th day of March 1899.
ABEL & IMRAY,
Agents for the Applicant.
I, RAYMOND COMBRET, of 18, Rue Mogador, Paris, France, Doctor of Medicine, 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:-
My invention relates to an improved process for tanning and treating hides and
skins of all kinds which consists in treating them on issuing from the rincing or
soaking process with very weak solutions of formic aldehyde containing systematically
determined quantities of free acids, which may however be varied according to the
nature of the hides treated, such treatment being effected in suitable vessels either
at the temperature of the surrounding atmosphere or preferably at a moderated
temperature in closed vessels to which motion is imparted by mechanical means.
My improved process for utilising the essential and direct tanning action of
formic aldehyde differs entirely from the experiments which have hitherto been
made with such aldehyde in the ordinary tanning processes; it also differs from the
various trials that have been made for utilising such aldehyde directly as the principal
tanning agent.
In carrying out my improved process the general rule is observed of never, during
the course of the tanning process and in particular at the commencement putting
fresh swelled hides or skins in direct contact with liquors which only contain formie
aldehyde in solution, no matter how weak, it being absolutely necessary in all cases
that there shall be simultaneously present, in the liquor up to the end of the process

page_text: a sufficient quantity of free acids (whether these are produced from the fermentation
of old liquors, or are freshly added), because the methodical combination of these
two actions of the formic aldehyde and of the free acids alone enables advantageous
practical results to be obtained.
In carrying out my improved process the same precautions have to be taken as
in the ordinary tanning process, that is to say, the first liquors must be comparatively
weak as to the tanning agent and strong as to the acid constituents, and in the sub-
sequent treatment the tanning agents should be gradually increased in strength
while the acid constituents are decreased.
In observing this rule with my improved process, it must be taken into account
that the tanning action of the formic aldehyde is very much more rapid than that of
all known tanning agents and that consequently it is necessary to modify the propor-
tions of the several ingredients accordingly.
For this purpose there may be used any kind of acid but I prefer to employ acetic
acid, which is miscible in all proportions with formic aldehyde, and is very efficaceous
for effecting and maintaining the swelling of the hides and skins, although its action
is gentle and easily regulated.
This acid can be readily produced by the lixiviation of exhausted tanning powders
in which glucoses may if necessary have been fermented; it may also he obtained by
treating the crude acetates derived from the pyrogenous distillation of wood or other
vegetable matter, whereby at the same time the quantities of formic aldehyde neces-
sary for my process are obtained by means of methylic alcohol, so that the new process
is thus rendered very economical.
The acetic acid can, if necessary, be replaced by other acids, in particular lactic
acid, which exists simultaneously therewith in the acid liquors of tanneries, but in
this case it is necessary to use from 20 to 25 p.c. more. If on the other hand sul-
phuric acid is used, from 20 to 25 p.c. less must be used. Oxalic acid can also be
employed but in about double the quantity of the lactic acid.
The quantity of acid (commercial acetic acid of 40° Bé.) employed at the commence-
ment can be much greater than the formic aldehyde (ordinary commercial solutions) for
instance in the proportion of about ten to one; but in that case the hides must be
rapidly transferred to liquors stronger in formic aldehyde, or this ingredient must
be gradually strengthened in the same liquor.
Towards the end of the tanning process, on the other hand, the aldehyde can be
present in greater proportion than the acid, but this excess of acid must be in
proportion to the excess of acid at starting.
A good practical result will be obtained for example if at the commencement
the well prepared hides are treated with a liquor containing from three to five
times as much acid as aldehyde, and subsequently solutions are employed either in
the same vat or in different ones, having the successive proportions of 4 of acid to 2
of aldehyde, 4:3, and 4:4. The process may either be stopped there, or the
successive variation of the proportion may be continued until there is from 4 to 5
times as much aldehyde as acid. As a rule this latter treatment would be limited to
large hides, and the process would be carried on rapidly, particularly towards
'the end.
As to the absolute quantity of formic aldehyde necessary for the complete
conversion of the hides into leather this may be very weak at starting, 1000th part
th even for large hides. A
of the solution for example, and never exceeding
25
1000
2.5
5
beginning may be made with
or
of the solution, finishing with
1000
1000
10
15
to
1000 1000°
The liquor used as solvent may for example be the acid juices of
spent tan; in this case the acidity of the liquor would be increased if necessary until
the above named proportions are obtained..

page_text: In practically carrying out my invention the following proportions may be used
with advantage.
1. FOR LARGE STRONG HIDES.
To 1,000 litres of water, with 10 to 15 litres of acid, there are taken from 1 to
5 1-5 litres of formic aldehyde at starting, then the proportions are successively
increased to §, f, f
until the inverse of the proportion at starting is
reached, that is to say, 1 to 1-5 litres of acid to from 10 to 15 litres of
aldehyde.
These relative differences would be about the highest in other cases the
proportion of acid may be diminished only to one half or one quarter of the
original dose, while still farther increasing the dose of aldehyde at the finish; for
2.5 aldehyde.
example
at starting, then successively
15 acid
1000
to
1.000
10 acid
5 aldehyde.
with 1,000 tres of water may be used WITH avuige at stating
formic aldehyde and 10-litres of acid, then 1, 18 and if necessary + &c.
3. FOR SMALL HIDES OR SKINS.
With 1,000 litres of water are used consecutively 15, 10 and 5 litres of acid with
respectively 2.5, 5, 10 or if necessary, 15 litres of formic aldehyde, the process being
carried on rapidly, more particularly towards the end.
The treatment can be carried on either at the atmospheric temperature and in
any kind of moveable or fixed receptacles, but it is very advantageous to employ
closed and mechanically moved vessels, such as revolving drums and the like working
at moderate temperatures.
The process may be completed in a few hours for small skins, and in two or three
days for the largest hides.
Skins with the wool or feathers and the like may be effectually and rapidly treated
in a single bath of equal parts of formic aldehyde and of acid or a little more of the
latter.
If it be desired to obtain white leathers, the process is carried out with pure
water, but the hides may be dyed more or less either before, during or after the
tanning, by means of coloured extracts for example of oak, chestnut, fir &c., or they
may be dyed various colours, such as yellow, blue, red, &c, or have a metallic lustre
imparted to them or be otherwise treated in any known manner for rendering them
waterproof.
They may also be supplementally treated with ordinary tanning agents or
extracts, but such subsequent treatment would not be with a view to perfect the
tanning process above described, as this leaves nothing to be desired as regards the
perfect tanning of the hides or skins, and the subsequent treatment would only
be with a view to modifying their appearance or texture, such as for imparting
to them the appearance of ordinary tanned leather.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
1. Process for tanning and treating hides and skins which consists in treating
the said hides and skins in solutions or liquors containing small quantities of
formic aldehyde in combination with systematically determined quantities of free
acids, in particular acetic acid, such treatment being effected either at atmospheric

page_text: temperature or preferably at a moderate temperature in closed vessels having motion.
imparted thereto substantially as herein described.
2. In the process for tanning and treating hides and skins referred to in
the First Claim; the employment for the combined formic aldehyde and free
acid solutions, of, from. th to
1000 1000th parts of formic aldehyde and from
25.
1000
1
25
th to 5th parts of free acid, substantially as described.
1000
3. In combination with the process referred to in the First and Second Claims, the
supplemental application of the known liquors, extracts, tanning materials, or dye
stuffs, for imparting to the hides the desired tints or for increasing their weight
and rendering them similar to leather of existing manufacture, substantially as
described.
4. The application of the process referred to in the First and Second-Claims to all
kinds of leather manufacture such as white leathers, chamois leathers, bides or skins
having the furs or feathers left thereon, which hides or skins. may be subsequently
rendered waterproof or otherwise treated for rendering them applicable to various
industrial applications, substantially as described.
Dated this 16th day of December 1899.