Improvements in and relating to the Manufacture and Treatment of Leather.
Year: 1897

page_text: Date of Application, 6th Nov., 1697
Complete Specification Left, 29th July, 1898-Accepted, 22nd Oct., 1898
Date of Application, oLN NOV., 1031
Complete Specification Left, 29th July, 1898-Accepted, 22nd Oct., 1898
"
[Communicated from abroad by DR, CARL DREHER, of Hochst-on-the-Main, in the
Empire of Germany, Analytical Chemist.]
Improvements in and relating to the Manufacture and Treatment of
Leather.
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 to be as follows:-
It is generally known that hides and skins are converted into leather of every
description and widely varying qualities by being, after the usual preparation,
treated with tan solutions, so that they become "filled" or impregnated with tan.
It is this complete process of making the tanning agents settle in the hide, as it
were, in a proper manner and in sufficient proportions,-after having
subjected such hide to the necessary preparatory dressing (consisting
of such operations as sweating, steeping in lime, removing the hair
and, if required, swelling) that is described by the comprehensive term of tanning;
and it is by the tanning process, such as it has been known hitherto, that all the
so-called dressed" or tanned leather, as found in the market, is obtained.
Now all the different kinds of leather are seriously deficient in one respect;
when brought into contact with water-especially warm water-they yield up to
such water, according to the length of time and intensity of its action, a greater
or less portion of the tan they had previously absorbed; or in other words, they, to
a greater or less extent, lose the characteristics of leather, become no leather at
all in a sense, and are found wanting in those very properties which users of
leather particularly value.
"
Of this anyone may readily satisfy himself by putting a small piece of flawless
sole-leather, for example, in boiling water. The water will quickly become tinged
an intense yellow by the tan extracted from the leather. While the leather itself
dwindles down to a lump not unlike a piece of india rubber in appearance, which,
while moist, is plastic, but not elastic, but, as it dries, becomes a brittle mass, hard
and stiff as horn.
There exists, indeed, another method of tanning leather, viz. what is known as
chrome-tanning: according to this method, chromic oxide is "filled" or forced'
into the pores of the hide, after the latter has been suitably prepared. The
chrome-leather," resulting from this process of dressing, is absolutely proof
against any action of water; but then the scope of its practical applicability is
very limited, seeing that the impregnation of it with chromic oxide has the effect

page_text: of depriving it of one of the most desirable qualities of leather particularly for the
boot and shoe trade-namely, porosity, Besides, for many other purposes, chrome-
leather is too smooth.
As before stated, the peculiarity of tanned leather, observed hitherto, has been,
that it was apt to part with its tan when brought into contact with water; and it
does so more especially when steeped in hot or warm water, or when "kneaded
(pressed or wrinkled) in water.
"
Now it has been discovered that leather may be rendered insensitive to any such
influence of the water by being treated with a solution of form-aldehyde, which
fact appears to be accounted for by the property, possessed by that substance, of
combining with the tannic acid in the cells of the leather, and forming a com-
pound insoluble in water.
Certain investigations and experiments are known to have been made before
now, which have shown that form-aldehyde, in the state of an aqueous solution,
will invariably form a chemical compound with the tan, whenever any so-called
condensing or binding agents, such as minerals acids, chloride of zinc or the like,
are present. These chemicals, however, exercise a decidedly injurious action upon
the leather. What would consequently be required is, that the form-aldehyde in
the cellular tissue should be in such a state of concentration, that the binding"
may proceed without the aid of the condensing agents just mentioned. But then
a concentrated solution of form-aldehyde seriously impairs the cellular fibre, and
more particularly the grain, of the leather, by attacking which, it renders the
leather hard, non-elastic and brittle.
Hence it follows.
A
(1) That in order to effect the desired chemical combination, it is necessary to
subject the tan in the cells to the action of form-aldehyde in a state of strong
concentration.
(2) That the cellular tissue should, as far as practicable, be protected from the
contact or influence of strong form-aldehyde solutions; and
(3) That, in most cases, special media should be resorted to in order to temper,
or check altogether, the injurious action of such solutions upon the cellular tissue
of the hide, generally, and upon the grain, in particular.
The first of these results is attained by incorporating into the hide or leather a
suitably diluted aqueous solution, and then concentrating such solution by allow-
ing it to dry on (and in) the leather, when the requisite chemical reaction will
take place.
or dress-
In the case of thin leather the form-aldehyde may be added to the ooze direct.
Leather of medium thickness should first undergo a preliminary tanning
ing process, form-aldehyde being added to the last or finishing liquors.
And thick leather is tanned finally, in the usual manner, and then steeped in 4
a solution of form-aldehyde.
In accordance with this method of operation a one-half to five per cent. solution
of form-aldehyde (proportioned to suit the kind of leather to be dealt with, as
hereinabove explained) should be provided.
It will, of course, be understood that the leather should not, prior to its treat- 4
ment with form-alderyde, be subjected to the action of any substances likely to
prevent, or interfere with, the absorption of the form-aldehyde solution by the
leather.
The maximum period of time, during which the solution should be allowed to
act upon the leather is 48 hours, but may be less, according to the quality or thick-
ness of the leather. The process of desiccation is as usual.
The second of the desiderata above enuciated is fulfilled by carrying dilution
as far as may be consistent with the practical requirements in each case.
As to the third condition, viz., the employment of agents which, during desicca-
tion, shall counteract any injurious effect of the form-aldehyde upon the cellular 5
tissue, it may be complied with in various ways:
In the case of somewhat thick leather, the grain side of the leather may, as the

page_text: drying progresses, be carefully moistened again with water; this will protect the
grain, being the particularly sensitive part of the leather.
In other cases the object of protecting the tissue from injurious influences, after
treatment with form-aldehyde, may effectually be accomplished by coating the
grain of the leather, before drying, with oil, fatty matter or any other readily
penetrating substance. Of course the oil, grease, or the like, should be used
sparingly, as too much of it would interfere with the action of the form-aldehyde
upon the tan. Or the same effect as that obtainable with fat and oil may, in the
case of certain sorts of leather, be produced by carefully manipulating the leather
with solutions or substances having the property of counteracting any further
effect of the form-aldehyde upon the cellular tissues, after these have absorbed a
sufficient amount of that chemical. Among the various agents that will answer
this purpose I may mention, for example, alkaline solutions, or substances capable
of bringing about alkaline reactions; also, finely divided metallic oxide, mixed
with water, alcohol, glycerine or fatty matter; which solutions should be rubbed
into the leather, on the grain side, prior to drying. All alkaline solutions, and
all solutions of alkaline carbonates and alkaline sulphides (sulpho-alkalies), as
well as pasty mixtures of magnesia, will be found suitable for this purpose; and
in making the proper selection, in each case, it is only essential that one point
should not be overlooked, viz. that the given solution, after having been applied
to the leather, should be capable, when done with, of being removed again without
any detriment to the goods.
Hygrometrical substances, also, will exercise a beneficial action in this respect
if applied to the leather after desiccation; provided they are free from any pro-
perties likely to make them influence the leather in some other undesirable manner;
and these, too, should be readily removable after use. Glycerine, however,
need
be removed,
not
when it has entered the
the
of
as,
pores
leather, it not only leaves the colour of that material quite unimpaired, but in
point of fact serves to keep up therein the very desirable qualities of elasticity and
moistness. But solutions of such substances as calcium chloride must be thoroughly
washed off with water, after having been allowed to act as required upon the cellular
tissue and grain.
It may be observed, that the form-aldehyde may also be employed in (or with)
other suitable media.
It will be understood that leather which, with the valuable properties of elasticity
and porosity combines that of not being injuriously affected by water, must be a
most welcome acquisition to all leather-consuming trades; for, as we all know,
there is scarcely a form of leather goods but is, at one time or another, brought
into contact with water or moisture; jack-boots and other boots and shoes, the
straps used in harnessing and saddlery, the leather used in connection with steam
and water pipes, the leather valves of some machines, and the belts employed in
driving machinery may serve as instances of this; driving belts especially, when
used, say, in dye-works, being very much exposed to influences of water and steam.
In all these cases they very rapidly lose some of their strength, durability and
elasticity, owing to the fast, that the water, at each successive contact with the
leather, quickly and energetically drains it of some of its tan; the amount of the
tan thus extracted varying with the closeness and duration of the contact. The
consequence is that the leather shrinks, loses its density or impermeability, becomes
hard and non-elastic on drying, and presently is found to be no more fit to answer
the purpose to which it is applied, than it was, when in its natural condition of
hide or skin.
All these drawbacks are obviated by the new process herein described, which
imparts to the leather an increased lasting power, thereby rendering it, for all
purposes, more serviceable than it was before.
It may also be mentioned, in conclusion, that, unlike ordinary tanned leather,
the leather prepared by this process will successfully go through all improving
operations, such as finishing, dyeing, and the like, performed by the aid of heat;

page_text: because it is capable of resisting the action of even boiling aqueous solutions,
which, however should not contain any too strong acids or alkalies, as will be
understood.
TYL
J
1007
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C.,
Agents for the Applicant.
Improvements in and relating to the Manufacture and Treatment of
Leather.
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 generally known that hides and skins are converted into leather of every
description and widely varying qualities by being, after the usual preparation,
treated with tan solutions, so that they become filled" or impregnated with tan.
It is this complete process of making the tanning agents settle in the hide, as it
were,--in a proper manner and
in sufficient proportions, after having
subjected such hide to the necessary preparatory dressing (consisting
of such operations as sweating, steeping in lime, removing the hair
and, if required, swelling) that is described by the comprehensive term of tanning;
and it is by the tanning process, such as it has been known hitherto, that all the
so-called "dressed" or "tanned leather, as found in the market, is obtained.
Now all the different kinds of leather are seriously deficient in one respect;
when brought into contact with water-especially warm water-they yield up or
give off to such water, according to the length of time and intensity of its action,
a greater or less portion of the tan they had previously absorbed; or in other words,
they, to a greater or less extent, lose the characteristics of leather, and are found
wanting in those very properties which users of leather particularly value.
"
Of this any one may readily satisfy himself by putting a small piece of flawless
sole-leather, for example, in boiling water. The water will quickly assume an
intense yellow tint by the tan extracted from the leather, while the leather itself
dwindles down to a lump not unlike a piece of india-rubber in appearance, which,
while moist, is plastic, but not elastic, but, as it dries, becomes a brittle mass, hard
and stiff as horn.
"
There exists, indeed, another method of tanning leather, viz., what is known as
chrome-tanning according to this method, chromic oxide, is "filled or forced into
the pores of the hide, after the latter has been suitably prepared. The "chrome-
leather," resulting from this process of dressing, is absolutely proof against any
action of water; but then the scope of its practical applicability is very limited,
seeing that the impregnation of it with chromic oxide has the effect of depriving
it of one of the most desirable qualities of leather essential particularly for the boot
and shoe trade-namely, porosity. Besides, for many other purposes, chrome-
leather is too smooth.
As before stated, the peculiarity of tanned leather, observed hitherto, has been,
that it was apt to part with its tan when brought into contact with water; and it
does so more especially when steeped in hot or warm water, or when kneaded"
(pressed or wrinkled) in water.
"
Now it has been discovered that leather may be rendered insensitive to any such
influence if treated with a solution of form-aldehyde, which fact appears to be

page_text: accounted for by the property possessed by that substance, of combining with the
tannic acid in the cells of the leather, and forming a compound insoluble in water.
Certain investigations and experiments are known to have been made before
now, which have shown that form-aldehyde, in the state of an aqueous solution
will invariably form a chemical compound with the tan, whenever any so-called
condensing (or binding agents), such as mineral acids, chloride of zinc or the like,
are present. These chemicals, however, exercise a decidedly injurious action upon
the leather and must therefore not be used. What would consequently be required
is, that the form-aldehyde in the cellular tissue should be in such a state of con-
centration, that the binding" may proceed without the aid of the con-
densing agents just mentioned. But then a highly concentrated solution of form-
aldehyde seriously impairs the cellular fibre, and more particularly the grain, of
the leather, by attacking which, it renders the leather hard, non-elastic and brittle.
Hence it follows:
1. That in order to effect the desired chemical combination, it is necessay to
subject the tan in the cells to the action of form-aldehyde in a state of strong
concentration;
2. That the cellular tissue should, as far as practicable, be protected from the
contact with or influence of strong form-aldehyde solutions, and
3. That, in most cases, special media should be resorted to, in order to temper,
or check altogether, the injurious action of such solutions upon the cellular tissue
of the hide, generally, and upon the grain, in particular.
The first of these results is attained by incorporating into the cells of the hide
or leather a suitable diluted aqueous solution, and then concentrating such solution
by allowing it to dry on (and in) the leather, when the requisite chemical reaction
will take place.
In order to effect this combination of form-aldehyde and tannic acid in leather,
great difficulties are encountered, and it is the object of the present invention to
successfully overcome these difficulties.
As the said substances have the quality of easily combining in the presence of
so-called chemical condensing agents, such as mineral acids or chloride of zinc, the
simplest method would be, to introduce into the cells of the leather the compound
thus obtained.
It is, however, found that these condensing agents are directly injurious to the
leather, seeing that they destroy the cellular tissue, so that in this direction
nothing can be done.
It has further been found, that only concentrated solutions of formaldehyde will
combine with tan, while at the same time it has been found, that concentrated
solutions of formaldehyde, directly attack the cellular tissue of the leather, and
that, on the other hand, very dilute solutions will under certain conditions exercise
no injurious effect upon the cellular tissue of the leather, provided that certain
precautionary measures be taken.
Hence it follows:
1. That, in order to enter into a chemical combination with the tan, the form-
aldehyde must be present in the leather in a concentrated state.
2. That, on the contrary, only as weak a solution as possible should be intro-
duced into the leather, and
3. That in most cases special media should in addition be applied, in order to
protect the cellular tissue of the leather, and more especially the grain from the
injurious action of the formaldehyde.
These three conditions now are complied with in the following manner:
As, according to the above points only weak solutions of formaldehyde should be
brought into the leather, whereas a chemical combination with the tan takes place
only in the case of a concentrated solution being present, I may proceed in such
a manner that only a weak solution is introduced into the leather, this weak
solution however, being concentrated in the leather itself by drying.

page_text: In the case of thin leather the formaldehyde may be added to the ooze or tan-
bath direct.
Leather of medium thickness should first undergo a preliminary tanning or
dressing process, by being placed in a solution of tannic acid, formaldehyde being
added to the last or finishing liquors.
In the case of thick leather the tanning operation is first entirely completed
whereupon the leather is steeped in a solution of formaldehyde.
In accordance with this method of operation a solution of one-half to five per cent.
of formaldehyde (proportioned to suit the kind or thickness of leather to be dealt
with, as hereinabove explained) should be provided.
It will, of course be understood that the leather should not, prior to its treat-
ment with formaldehyde, be subjected to the action of any substances likely to pre-
vent, or interfere with, the absorption of the formaldehyde solution by the leather,
such as oil, or fatty substances or the like.
The maximum period of time, during which the solution should be allowed to
act upon the leather is 48 hours, but may be less, according to the quality or thick-
ness of the leather. The process of desiccation is as usual.
The second of the desiderata above enunciated is fulfilled by exposing the leather
as little as possible to the injurious action of the formaldehyde, this result being
achieved by applying to the leather the least possible quantity of formaldehyde
provided that the latter be still sufficient to obtain the purpose in view.
As to the third condition, viz. the employment of agents which, during desicca-
tion, shall counteract any injurious effect of the formaldehyde upon the cellular
tissue, it may be complied with in various ways.
In the case of somewhat thick leather, the grain side of the leather may, as the
drying progresses, be carefully moistened again with water; this will protect the
grain, being the particularly sensitive part of the leather.
In other cases the object of protecting the tissue from injurious influences, after
treatment with formaldehyde, may effectually be accomplished by coating the grain
of the leather, before drying, with oil, fatty matter or any other readily penetrating
substance.
Of course, the oil, grease, or the like, should be used sparingly, as
too much of it would interfere with the action of the formaldehyde upon the tan.
Or the same effect as that obtainable with fat and oil may, in the case of certain
kinds of leather, be produced by carefully manipulating the leather with solutions
or substances having the property of counteracting any further effect of the form-
aldehyde upon the cellular tissues, after these have absorbed a sufficient amount
of that chemical. Among the various agents that will answer this purpose I may
mention for example, alkaline solutions, or substances capable of bringing about
alkaline reactions; also, finely divided metallic oxides, mixed with water, alcohol,
glycerine or fatty matter; which solutions should be rubbed into the leather, on
the grain side, prior to drying. All alkaline solutions, and all solutions of alkaline
carbonate and alkaline sulphides (sulpho-alkalies), as well as pasty mixtures of
magnesia, will be found suitable for this purpose; and in making the proper
selection, in each case, it is only essential that one point should not be overlooked,
viz. that the given solution, after having been applied to the leather, should be
capable, when done with, of being removed again without any detriment to the
goods.
Hygrometrical substances, also, will exercise a beneficial action in this respect
if applied to the leather prior to its desiccation; provided they are free from any
properties likely to make them influence the leather in some other undesirable
manner; and these, too, should be readily removable after use. Glycerine, how-
ever, need not be removed, as, when it has entered the pores of the leather, it not
only leaves the colour of that material quite unimpaired, but in point of fact
serves to keep up therein the very desirable qualities of elasticity and moistures.
But solutions of such substances as calcium chloride must be thoroughly washed
off with water or the like, after having been allowed to produce their moistening
effect upon the cellular tissue and grain, during the drying of the leather.

page_text: It is however impossible to state in general, the percentage in which these sub-
stances should be applied, which percentage depends upon the circumstances and
experience.
The properly tanned sole-leather, as it comes from the tan-pit, and while yet
moist, is, for 48 hours, and at an ordinary temperature, placed in a solution of
formaldehyde, containing approximately 2 parts of form-aldehyde for every 100
parts of water. The leather is then removed from the solution and the liquor still
adhering to it allowed to drip off; after which it is several times, rubbed-in with
glycerine, and lastly dried in the usual manner. When leather thus treated is
placed in boiling water, little or no tan will ooze out of it, and even after having
been boiled in water and dried again, it will, so far as its outwardly properties are
concerned, not be distinguishable from ordinary tanned leather of like quality,
but which has not been treated by the new process.
It may be observed, that the formaldehyde may also be employed in (or with).
other suitable media such as alcohol.
It will be understood that leather which, with the valuable properties of clasticity
and porosity combines that of not being injuriously affected by water, must be a
most welcome acquisition to all leather-consuming trades; for, as well known, there
is scarcely a form of leather goods but is, at one time or another, brought into con-
fact with water or moisture; jack-boots and other boots and shoes, the straps used
in harness and saddlery; the leather used in connection with steam and water
pipes, the leather valves of some machines, and the belts employed in driving
machine may serve as instances of this; driving belts especially, when used, say,
in dye-works, being very much exposed to the influence of water and steam. In
all these cases leather very rapidly loses some of its strength, durability and
elasticity, owing to the fact, that the water, at each successive contact with the
leather, quickly and energetically drains it of some of its tan; the amount of the
tan thus extracted varying with the closeness and duration of the contact. The
consequence is that the leather shrinks, looses its density or impermeability,
becomes hard and non-elastic on re-drying, and presently is found to be no more
fit to answer the purpose to which it is applied, than it was, when in its natural
condition of hide or skin.
All these drawbacks are obviated by the new process herein described, which
imparts to the leather an increased lasting power thereby rendering it, for all pur-
poses, more serviceable than it was before.
It may also be mentioned, in conclusion, that, unlike ordinary tanned leather,
the leather prepared by this process will successfully go through all improving
operations, such as finishing, dyeing and the like, performed by the aid of heat;
because it is capable of resisting the action of even boiling aqueous solutions, which
however should not contain any too strong acids or alkalies, as will be understood.
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 employment of formaldehyde for the purpose of binding" (or fixing)
the tan in the leather, so as to render it insoluble in water; the formaldehyde
being for this purpose, in the form of a dilute solution, introduced into the leather
and then allowed to dry thereon (or therein).
2. In the employment of formaldehyde, in accordance with the 1st Claim, the
use of suitable agents capable of reducing or neutralizing the injurious action of
the formaldehyde upon the cellular tissue, during the drying stage.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C.,
Agents for the Applicant.