An Improved Process and Composition for Tawing Skins in the Manufacture of Leather.
Year: 1899

page_text: PROVISIONAL SPECIFICATION.
An Improved Process and Composition for Tawing Skins in the
Manufacture of Leather.
I, GEORGE WASHINGTON ADLER, residing at North-east Corner of 25th and
Norris Streets, City of Philadelphia, State of Pennsylvania, United States of
America, do hereby declare the nature of this invention to be as follows:-
My invention relates to the art of tawing skins in the manufacture of leather,
and belongs generally to the class of mineral tannages, and specifically to the
class in which compounds of chromium are employed as the tawing agents,
whether the same be applied to a raw skin prepared for tanning or to such a skin
which has been already tawed by compounds of aluminum salts.
My invention consists of the process and composition hereinafter described,
whereby the oxides or basic salts of aluminum and of chromium are separated
out of their compounds in the presence of the skin and insolubly combined with
the tissues thereof, resulting in the production of an insolubly tawed skin, which
partakes of the nature of both alum tawed leather and chrome tawed leather,
in that it possesses the appearance, touch, fine grain and softness characteristic
of and peculiar to the former, while it has also the perfectly insoluble nature
which distinguishes the latter.
The essential feature of my discovery is that the reduced salts of chromium
commonly known as chrome alum will, when compounded with an alkali salt of
an organic acid, such as potassium acetate, and with the necessary
sodium salts required for tawing purposes to make proper leather, such as equal
parts of sodium sulphate and sodium chloride, make a tawing composition in
which when the skin is exhibited thereto, a chemical reaction will take place, in
which the chromic oxide is separated out from its salt and becomes insolubly
combined with the hide tissue.
For the purpose of preparing the skins in order that a better quality of
leather may be produced, I deem it advantageous to first taw the skins in alum
and salt, preferably employing aluminum sulphate, after which the skins are
given a treatment with hyposulphite of sodium, sometimes called sodium thio-
sulphate. As the tendency of hyposulphite of sodium is to thin the skin, that
effect may be overcome by a subsequent weak bath of alum and salt.
I will now proceed to describe the method which I have found the best for
carrying out my process.
For every 100 pounds of skins, prepared for tanning I prepare a solution in
two gallons of water of three pounds of aluminum sulphate and six pounds of
fine common salt. This liquor is put in the drum with the skins, and run for
about half an hour. I then prepare a second solution by dissolving about ten
pound of hyposulphite of soda in about three gallons of warm water and add this
solution to the liquor and skins still in the drum and run the drum for about
fifteen or twenty minutes. If the skins are thinned much by the hyposulphite,
I then prepare a third solution by dissolving about one pound more of aluminum
sulphate and two pounds more of fine common salt, and this solution is also added
D
077

page_text: to the liquor and skins in the drum. The skins are now run in this liquor for
a half hour or more, or longer if need be, until the skins show on inspection
that they have acquired the requisite plumpness. The skins are then preferably
taken from the drum and rinsed off by a single dipping of them separately in
clean water, and then horsed up for several hours or several days as may be
desired; but this is not necessary.
The quantities of materials used as above specified, may be varied slightly
in the three several steps while retaining the proportions substantially as stated.
For economy of operation I have described the three several solutions as being
exhibited to the skins in the same drum in a certain order at intervals, but the
same results are obtained if the skins are submitted to the three solutions sepa-
rately but consecutively and in the order described.
The old liquor need not be drawn off from the drum as the skins will take up
the most of it, under the above formula. They are then to be treated in the
drum by my initially chemically neutral chrome liquor hereinafter described,
which is then to be introduced, and without adding water or free acid of any
kind. For this bath I employ not less than three nor more than six gallons of
such chrome liquor to each one hundred pounds of skins. The chrome liquor is
compounded as follows:-
I dissolve in five gallons of water about six pounds of chrome alum, three
pounds of sodium sulphate, three pounds of sodium chloride and half a pound of
potassium acetate.
The skins are run in the drum in this liquor for about an hour, or until they
have taken up all or nearly all the liquor and show thorough penetration of the
chromic compound. At this stage they will be found to be perfectly insoluble
in hot water. They can then be removed from the drum and washed and finished
as usual in kid leather dressing.
For extra heavy skins the neutral chrome liquor may be increased to seven
gallons or more to each one-hundred pounds of skins. As the active sodium salt
in this solution is the sulphate, the chloride being used only to prevent tighten-
ing of the skin fibres, the chloride may be omitted if the sulphate of sodium is
increased by an amount equal to one-half the weight of the chloride as given in
the above formula. It may also be observed that the quantities of each ingredient
named may be varied slightly provided the proportions stated be substantially
retained.
Modifications of this process may be made as follows; namely, in making up
of chrome liquor, hyposulphite of sodium may be substituted in equal quantity
for the aggregate of sodium sulphate and sodium chloride; and such a composi-
tion may be applied to the skins prepared for tanning without the previous
treatment by aluminum sulphate and salt or alum and salt; or the two latter
ingredients may be added to the chrome composition. Certainty however, in
the treatment of the skins will be best obtained by following the formula which
I have first above described.
Another advantage in the use of this process and composition in the manufac-
ture of kid leather is that it is entirely consistent with the beam house treatment
which formerly obtained by means of the bran drench in lieu of puring in the
preparation of the skins for tanning.
It has been well known for many years that chrome alum and aluminum sul-
phate and compounds of either or both of them with their chemical agents may
be and have been heretofore frequently employed successfully in the tawing of
skins but the leather so produced has been objectionable in that there was no
insoluble fixation of the hide fibres. Others have heretofore chrome-tawed skins
by exhibiting them to a chromic acid solution and then to a reducing bath of
hyposulphite of soda and acid; but my process consists of exhibiting to the skins
a reduced salt of chromium, and fixing the same insolubly on the skin tissues,
which has never been heretofore accomplished. I have discovered however, that
when this reduced chromic salt is exhibited to the skin in the presence of an

page_text: alkali salt of an organic acid of the class of sodium or potassium acetate in con-
junction with sodium sulphate or sodium thiosulphate in proper relative pro-
portions, there takes place in the presence of the organic substances of the hide,
a decomposition of the reduced metallic salts, which is perhaps a separating out
of its basic salt or oxide and an insoluble fixation of the hide fibres is produced.
While my improved process is applicable to the tawing of all kinds of skins,
it is more particularly designed for use in the manufacture of kid
and other light leathers for which as is well known, alum tannages or
combinations thereof having alum as the base, are best adapted and produce the
best results. I may also add that my process is best applied and productive of
the desired result with greater economy of material, in a comparatively shorter
time, when a drum or other like mechanical apparatus is employed.
The process will not proceed with other than a neutral compound other than
as free acid may be produced in the reactions taking place after the skin is sub-
mitted to the solution. But it proceeds readily and completely by the aid of
the organic acid salts with the neutral metallic salt, in the presence of sodium
sulphate or of sodium thiosulphate; hence no free acid of any kind either or-
ganic or inorganic, is to be added to the solution. The separation out of the in-
soluble basic salt or oxide of chrome from its salts initially employed in the com-
position, and the concomitant reactions, take place directly on or in the presence
of the skin fibres, resulting in an insoluble fixation of the gelatinous tissues,
and with the additional advantage that the resultant tawed skin will have its
fibres less fixedly agglutinated and hence will require very much less staking
than usual.
1000
D. YOUNG & Co.,
11 & 12, Southampton Buildings, London, W.C.,
Agents for the Applicant.
An Improved Process and Composition for Tawing Skins in the
Manufacture of Leather.
I, GEORGE WASHINGTON ADLER, of North East Corner, 25th and Norris Streets,
City of Philadelphia, State of Pennsylvania, U.S.A., do hereby declare the nature
of this invention and in what manner the same is to be performed, to be par-
ticularly described and ascertained in and by the following statement:-
My invention relates to the art of tawing skins in the manufacture of leather,
and belongs generally to the class of mineral tannages, and specifically to the
class in which compounds of chromium are employed as the tawing agents,
whether the same be applied to a raw skin prepared for tanning or to such a skin
which has been first tawed by alum and salt or compounds of aluminum and
sodium salts.
My invention consists of the process and composition hereinafter described,
whereby the insoluble salts of chromium are separated out of chrome alum
compounds in the presence of the skin and insolubly combined with the tissue
thereof, resulting in the production of an insolubly tawed skin, which (if pre-
viously tawed with alum and salt) partakes of the nature of both alum tawed
leather and chrome tawed leather, in that it possesses the appearance, touch, fine
grain and softness characteristic of and peculiar to the former, while it has also
the perfectly insoluble nature which distinguishes the latter.
The essential feature of my discovery is that the reduced salts of chromium

page_text: commonly known as chrome alum, will, when compounded with an alkali salt of
an organic acid, such as potassium or sodium acetate, and with the necessary
sodium salts required for tawing purposes to make proper leather, such as equal
parts of sodium sulphate and sodium chloride, make a tawing composition in
which, when the skin is exhibited thereto, a reaction takes place, in which the
insoluble salt of chromium is separated out from its reduced compound and
becomes insolubly combined with the hide tissue.
For the purpose of preparing the skins in order that a better quality of
leather may be produced but not otherwise necessary, I deem it advantageous
to first taw the skins in alum and salt, preferably employing aluminum sul-
phate with sodium chloride, as commonly used, after which the skins may be
given a treatment with hyposulphite of sodium, sometimes called sodium thio-
sulphate, if a particularly smooth and fine grain is desired. As the tendency
of hyposulphite of sodium is to thin the skin, that effect if noticed, may be over-
come by a subsequent weak bath of alum and salt.
I will now proceed to describe the method which I have found the best for
carrying out my process.
For every 100 pounds of skins, prepared for tanning I prepare a solution in
two gallons of water of three pounds of aluminum sulphate and six pounds of
fine common salt. This liquor is put in the drum with the skins, and run for
about half an hour. For kid skins, I then prepare a second solution by dis-
solving about ten pounds of hyposulphite of soda in about three gallons of warm
water and add this solution to the liquor and skins still in the drum and run the
drum for about fifteen or twenty minutes. If the skins are much thinned by
the hyposulphite, I then prepare a third solution by dissolving about two pounds
more of aluminum sulphate and three pounds more of fine common salt, and this
solution is also added to the liquor and skins in the drum. The skins are now
run in this liquor for a half hour or more, or longer if need be, until the skins
show on inspection that they have acquired the requisite plumpness.
The quantity of materials used as above specified, may be varied slightly
in the three several steps, while retaining the proportions substantially as stated.
For economy of operation I have described the three several solutions as being
exhibited to the skins in a certain order, in the same drum at intervals but the
same results are obtained if the skins are submitted to the three solutions sepa-
rately but consecutively and in the order described.
The skins are now to be treated by my initially chemically neutral chrome
liquor hereinafter described, which is then to be introduced into the drum,
and without water or free acid of any kind. For this bath I employ not less
than three nor more than six gallons of such chrome liquor to each one hundred
pounds of skins. The chrome liquor is compounded as follows:--
I dissolve in five gallons of water about six pounds of chrome alum, three
pounds of sodium sulphate, three pounds of sodium chloride and half a pound of
potassium or sodium acetate.
The skins are run in the drum in this liquor for about an hour, or until they
have taken up all or nearly all the liquor and show thorough penetration of the
chromic compound. At this stage they will be found to be perfectly insoluble
in hot water. They can then be removed from the drum and washed and finished
as usual in kid leather dressing. For extra heavy skins the neutral chrome
liquor may be increased to seven gallons or more to each one-hundred pounds of
skins. It should also be observed that the quantities of each ingredient named
may be varied slightly provided the proportions stated be substantially retained.
Modifications of this process may be made as follows, namely in making up of
chrome liquor, hyposulphite of sodium may be substituted in equal quantity
for about half the aggregate of sodium sulphate and sodium chloride; and as a
further modification such a composition may be applied to the skins prepared
for tanning without the previous treatment by aluminum sulphate and salt or
alum and salt; or the two latter ingredients may be added to the chrome com-

page_text: position. Certainty however, in the treatment of the skins will be best obtained
by following the formula which I have first above described, although the pre-
vious treatment or tawing prior to the chrome treatment which is itself a taw-
ing, is not essential to make good leather.
Another advantage in the use of this process and composition in the manufac-
ture of kid leather is that it is entirely consistent with the beam house treatment
which formerly obtained by means of the bran drench in lieu of puring in the
preparation of the skins for tanning.
It has been well known for many years that chrome alum and aluminum sul-
phate and compounds of either or both of them with their chemical agents may
be and have been heretofore frequently employed successfully in the tawing of
skins; but the leather so produced has been objectionable in that there was no
insoluble fixation of the hide fibres. Others have heretofore chrome-tawed skins
by exhibiting them to a chromic acid solution and then to a reducing bath of
hyposulphite of soda and acid; but my process consists in exhibiting to the skin
a reduced salt of chromium, and fixing the same insolubly on the skin tissues,
which has never been heretofore accomplished. I have discovered however, that
when these reduced metallic salts are exhibited to the skin in the presence of an
alkali salt of an organic acid of the class of sodium or potassium acetate in pro-
per proportion in conjunction with sodium chloride and sodium sulphate or
sodium thiosulphate, there takes place in the presence of the organic substances
of the hide, a decomposition of the reduced metallic salt, which is perhaps a
separating out of its basic salt or oxide and an insoluble fixation of the hide
fibres is produced.
While my improved process is applicable to the tawing of all kinds of skins,
it is more particularly designed for use in the manufacture of kid and other light
leathers including sheep and calf, for which as is well known, alum tannages or
combinations thereof having alum as the base, are best adapted and produce the
best results. I may also add that my process is best applied and productive of
the desired result with greater economy of material, in a comparatively shorter
time, when a drum or other like mechanical apparatus is employed.
The process will not proceed with other than a neutral compound other than
as free acid may be produced in the reactions, taking place after the skin is sub-
mitted to the solution. But it proceeds readily and completely by the aid of
the organic acid salts with the neutral metallic salt, in the presence of sodium
sulphate or of sodium thiosulphate; hence no free acid of any kind either or-
ganic or inorganic, is to be added to the solution. The separation out of the in-
soluble metallic salts or oxides from their salts named as initially employed in
the composition, and the concomitant reactions, take place directly on or in the
presence of the skin fibres, resulting in an insoluble fixation of the gelatinous
tissues, and with the additional advantage that the resultant tawed skin will
have its fibres less fixedly agglutinated and hence will require very much less
staking than usual.
Having now particularly described and ascertained the nature of my said
invention, and in what manner the same is to be performed, declare that what
I claim is:-
1. The process of tawing skins prepared for tanning, which consists in sub-
mitting them in a suitable mechanical apparatus to the action of aqueous solu-
tions of aluminum sulphate with sodium chloride, and of chrome alum, either
together or successively, the chrome alum being exhibited in the presence of an
alkali salt of an organic acid, such as potassium or sodium acetate, with sodium
sulphate and sodium chloride or with sodium thiosulphate; substantially as
described.
2. In the art of tawing, the process described which consists in first subjecting
the skins prepared for tanning to the action of a solution of aluminum sulphate
and chloride oflium then further treating such skins in an aqueous solution

page_text: of hyposulphite of sodium, and finally adding to the bath a composition con-
sisting of chrome alum, potassium or sodium acetate, sodium sulphate and sodium
chloride; the skins being successively acted on by the bath in its several
conditions.
3. A tawing composition consisting of chrome alum, with or without alu-
minum sulphate, an alkali salt of an organic acid such as potassium or sodium
acetate, and sodium sulphate with sodium chloride; substantially as described.
4. A composition for tawing raw skins prepared for tanning, or for the pro-
duction of insoluble alum tawed skins by an after treatment of said tawed skins
with chromic salts, said composition consisting of an initially neutral aqueous
solution of chrome alum, an alkali salt of an organic acid such as potassium or
sodium acetate, with sodium sulphate and sodium chloride or with sodium thio-
sulphate; substantially as described.
Dated this 11th day of Sentember 1900.
D. YOUNG & Co.,
11 & 12, Southampton Buildings, London, W.C.,
Agents for the Applicant.