Improvements in Tanning.
Year: 1893

page_text: Date of Application, 30th June, 1893
Complete Specification Left, 28th Mar., 1894-Accepted, 28th Apr., 1894
Improvements in Tanning.
I, CHRISTIAN HEINZERLING, Ph.D., of 9 Rotteckstrasse, Frankfort-on-Main,
in the Empire of Germany, at present residing at the Holborn Viaduct Hotel,
Holborn Viaduct, in the City of London, do hereby declare the nature of this
invention to be as follows:-
It has before been proposed to employ compounds of chromium or other mineral
salts but hitherto the employment of such substances has been accompanied by some
disadvantages, namely:
1. The leather is wanting in weight.
2. The leather is thin and unfilled.
3. The leather cuts rough instead of smooth.
4. Generally the leather is not sufficiently capable of resisting the influence of
water.
In order to avoid the effect of washing, the leather containing the tanning
material (chromium or other mineral substance) was impregnated with fats or
paraffin which made it more or less waterproof or, when the tanuing was carried
out with chromic acid salts, they were reduced with ferro sulphate oxalic acid,
sulphurous acid, thiosulphuric acid, sulphuretted hydrogen &c. a process which is
only suitable for the manufacture of such kinds of leather in which no value is
placed upon a smooth cut and good weight. The reduction also of the chromic
acid in acid solutions appears detrimental to the ultimate quality of the leather.
Further, tanning with chromic acid salts or chromic oxide salts does not appear to
have been sufficiently observed so that the different chromium compounds behaved
very differently to the fibres of the hide. By complete investigation I have found
that a number of compounds of chromium may be employed to produce the various
qualities and grades of leather desired. The tanning process hereinafter described
is to obviate the above mentioned difficulties.
In my tanning process the following compounds of chromic acid, chromic and
chromous oxide are employed :-
Chromic chromate Cr₂(CrO4)2 formed either by dissolving chromic hydrate
(1 molecule) in the equivalent quantity of chronic acid (3 molecules) or by decom-
posing a salt of chromic oxide with compounds of chromic acid.
Bichromate monosulphate of chromium Cr₂(Cro),SO, formed either by dis-
solving 1 molecule of chromic hydrate in 2 molecules of chromic acid and 1 molecule
of sulphuric acid or by other suitable methods.
Basic chromate sulphate of chromium Cr2CrO4SO, formed by dissolving 1 mole-
cule of chromic hydrate in a solution of 1 molecule of chromic acid and 1 molecule
of sulphuric acid.
Chromate disulphate of chromium Cr₂CrO4(SO4)2 formed by dissolving 1 mole-
cule of chromic oxide in 2 molecules of sulphuric acid and 1 molecule of chromic
acid.
Aluminium chromate formed by dissolving an excess of aluminium hydrate in hot
chromic acid.
Chromic thiosulphate by decomposing salts of chromic oxide with salts of
thiosulphuric acid.
Chromic sulphite either by decomposing salts of chromic oxide with neutral or
acid sulphite salts or by saturating a solution of sulphurous acid with chromic
hydrate.

page_text: Ferrous hydrosulphite FeS,O.
Zinc hydrosulphite ZnS,O
Manganese hydrosulphite MnS₂O,
Sodium hydrosulphite Na2S2O.
formed by the action of the metal upon sulphurous acid or bisulphite of sodium.
In combination with the above named compounds there may be used the alkaline
salts of chromic acid already employed or chromic acid itself.
Among the above mentioned materials the compounds of chromic oxide with
chromic acid, the double salt of chromic oxide with chromic and sulphuric acids
chromic sulphite and chromic thiosulphate are especially efficaceous in tanning.
In carrying out the process of tanning the hides to be tanned are prepared
cleaned and deprived of hair according to the usual methods.
The hides prepared ready for tanning are first laid in a dilute solution of the
above mentioned compounds of chromic acid and chromic oxide and then the
solution is successively strengthened by putting in fresh quantities of the chromium
compounds. It is preferable to begin with ato per cent. solution and gradually
strengthen this to from 10 to 15 per cent. For heavy leather very concentrated
solutions should be used at the finish.
The length of time of the tanning depends upon the thickness and quality of
the hides heavy leather hides are left 5 to 8 weeks in the tan liquor.
The above mentioned chromium compounds can be used respectively alone
according as the various kinds of leather are desired or the hides may first be
tanned in the chromic acid compounds formerly employed and then finished in
solutions of the above mentioned chromic oxide salts or chromous oxide compounds
or vice versa that is to say the hides may first be tanned in the above recommended
chromic oxide salts and then put into one of the above mentioned compounds
containing chromic acid. The first method is however in most cases preferable.
The combination of chromic acids compounds and chromic oxide salts is
especially to be recommended when it is wished to obtain leather of good
weight.
The hides to be tanned may also be first tanned with alkaline salts of chromic
acid or chromic acid alone and then finished with chromic sulphite or chromic
thiosulphate or chromous oxide compounds. Also vice versa one may proceed by
first tanning in chromic sulphite or chromic thiosulphate and then finish in potassium
or sodium bichromate or chromic acid.
In place of chromic sulphite and thiosulphate, thiosulphate of iron, zinc,
manganese, aluminium, or the hydrosulphites of sodium, potassium, iron and zinc
may be used. The thiosulphates of these metals decompose, without addition of
acid, the chromic acid and the above mentioned chromic acid compounds; the
chromic acid is thereby reduced to chromic oxide or combines with the metallic
oxides with the result of precipitating metallic oxides in the fibres of the hide.

page_text: The hydrosulphurous acid salts (hydrosulphites of sodium, potassium, iron and
zinc) are far more efficaceous than the metallic thiosulphates for treating hides
which have been previously treated with chromic acid compounds or chromic acid.
Even the alkaline salts of hydrosulphurous acid effect the reduction of the chromic
acid and its compounds without addition of acid which is not the case with the
alkaline thiosulphates.
The metallic salts of hydrosulphurous acid are much more efficaceous than the
alkaline salts of the latter. The metallic salts thereby deposit metallic oxide
which not only tans but also gives colour. The chromic and chromous oxide salts
in use in my process reduce without any addition of acid the chromic acid and
chromic acid compounds. The chromous oxide salts mostly combine with the
fibres of the hide. The leather produced is thereby fuller and cuts smoother, the
tanning is more complete and the weight better than in the old method of chromate
tanning.
Whether and how the above mentioned chromic acid, chromic and chromous
oxide compounds may preferably be combined with one another or preferably used
alone of course depends upon what quality of leather it is wished to produce and
the colour it is desired to be.
Compounds of chromic chromate, chromate sulphate of chromium, chromic
thiosulphate, chromic sulphite are taken up so easily and in such great quantity by
the fibres of the hide and are retained so well that they may for some kinds of
leather be used alone for tanning.
If it be wished to obtain a very complete tanning of the leather and good weight
the above named combinations are preferably used.
If it be wished to produce an especially hard and solid leather, hide tanned with
the above mentioned chromium compounds is treated with barium thiocyanate, when
by decomposition there is formed chromium thiocyanate and the corresponding
barium salt which for the most part is deposited on the fibres of the hide.
The tanned hides for upper leather or other light leather as soon as they
come out of the tan liquor should be well washed, greased and dressed according to
the known methods.
If it be wished to produce coloured or black leather, the hides are preferably
colored or blackened before the greasing.
Hides intended for ordinary sole leather may not be washed but may be taken
out of the tan liquor dried and dressed in the usual way.
Dated this 30th day of June 1893.
DR. CHR. HEINZERLING.
COMPLETE SPECIFICATION.
Improvements in Tanning.
I, CHRISTIAN HEINZERLING, Ph.D. of 9 Rotteckstrasse, Frankfort-on-Main, in
the Empire of Germany, 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 has before been proposed to employ compounds of chromium or other mineral
salts but hitherto the employment of such substances has been accompanied by
some disadvantages, namely:-
1. The leather is wanting in weight.
2. The leather is thin and unfilled.
3. The leather cuts rough instead of smooth.
4. Generally the leather is not sufficiently capable of resisting the influence
of water.
In order to avoid the effect of washing, the leather containing the tanning
material (chromium or other mineral substance) was impregnated with fats or

page_text: paraffin which made it more or less waterproof or, when the tanning was carried
out with chromic acid salts, they were reduced with ferrosulphate oxalic acid,
sulphurous acid, thio sulphuric acid, sulphuretted hydrogen &c. a process which
is only suitable for the manufacture of such kinds of leather in which no
value is placed upon a smooth cut and good weight. The reduction also of
the chromic acid in acid solutions appears detrimental to the ultimate quality
of the leather. Further tanning with chromic acid salts or chromic oxide
salts does not appear to have been sufficiently observed so that the different
chromium compounds behaved very differently to the fibres of the hide. By
complete investigation I have found that a number of compounds of chromium
may be employed to produce the various qualities and grades of leather
desired. The tanning process hereinafter described is to obviate the above
mentioned difficulties.
In my tanning process the following compounds of chromic acid, chromic and
chromous oxide are employed :-
Chromic chromate Cr.(CrO4) formed either by dissolving chromic hydrate
(1 molecule) in the equivalent quantity of chromic acid (3 molecules) or by
decomposing a salt of chromic oxide with compounds of chromic acid.
Bichromate monosulphate of chromium Cr,(CrO4)2SO, formed either by
dissolving 1 molecule of chromic hydrate in 2 molecules of chromic acid and
1 molecule of sulphuric acid or by other suitable methods.
Basic chromate sulphate of chromium Cr,CrO SO. formed by dissolving
1 molecule of chromic hydrate in a solution of 1 molecule of chromic acid and
1 molecule of sulphuric acid.
Chromate disulphate of chromium Cr,CrO4(SO), formed by dissolving
1 molecule of chromic oxide in 2 molecules of sulphuric acid and i molecule of
chromic acid.
Aluminium chromate formed by dissolving an excess of aluminium hydrate in
hot chromic acid.
Cbromic thiosulphate by decomposing salts of chromic oxide with salts of
thiosulphuric acid.
Chromic sulphite either by decomposing salts of chromic oxide with neutral or
acid sulphite salts or by saturating a solution of sulphurous acid with chromic
hydrate.
Chromous chloride CrCl, formed by reducing chromic chloride Cr,Cl, with
zinc or iron.
Chromous sulphate CrSO, formed by reducing chromic sulphate Cr,(SO.),
with zinc dust or iron filings.
Chromium thiocyanate formed by decomposing barium thiocyanate with chromic
sulphate.
Ferrous thiosulphate FeS₂O,
Aluminium thiosulphate Al,(S,O,).
Zinc thiosulphate ZnS,O.
Manganese thiosulphate MnS,O3.
all four formed by decomposing barium thiosulphate BaS,Os with salts of sulphuric
acid or in other suitable manners.
--
Schützenberger's hydrosulphites also called Bernthsens hyposulphites :-
Ferrous hydrosulphite FeS,O.
Zinc hydrosulphite ZnS,O
Manganese hydrosulphite MnS,O,
2
1
דג

page_text: chromic acid, the double salt of chromic oxide with chromic and sulphuric acids
chromic sulphite and chromic thiosulphate are especially efficaceous in tanning.
In carrying out the process of tanning the hides to be tanned are prepared
cleaned and deprived of hair according to the usual methods.
The hides prepared ready for tanning are first laid in a dilute solution of the
above mentioned compounds of chromic acid and chromic oxide and then the
solution is successively strengthened by putting in fresh quantities of the chromium
compounds. It is preferable to begin with a toper cent. solution and gradually
strengthen this to from 10 to 12 per cent. For heavy leather such as sole leather
very concentrated solutions 15 to 20 per cent. should be used at the finish.
Preferably the hides are stirred in the tanning solution in order that rapid
shrinking of the grain may be avoided.
The length of the tanning depends:-
(1.) Upon the thickness and quality of the hides.
(2.) Upon the concentration of the liquor.
(3.) Upon the quality of the leather which is intended to be produced.
Thick sole leather may remain 5-6 weeks in the tau liquor, whilst lighter
upper leather is completely tanned in 8-14 days. The hides tanned as above
described are, when upper leather is to be made washed a short time in water
and greased in the usual way. Sole leather is preferably hung out to dry
without washing and further treated in known ways.
The above mentioned chromium compounds can be used respectively alone
according as the various kinds of leather are desired or the hides may first be
tanned in the chromic acid compounds formerly employed and then finished in
solutions of the above mentioned chromic oxide salts or chromous oxide
compounds or vice versa that is to say the hides may first be tanned in the above
recommended chromic oxide salts and then put into one of the above mentioned
compounds containing chromic acid. The first method is however in most cases
preferable.
Should the combined method be used and in such a manner that the hides
tanned in the mentioned compounds of chromic acid and chromic oxide are
placed in solutions of the before mentioned chromic oxide salts or chromic oxide
compounds or vice versa the hides coming from one solution into the other
solution must to obtain a good grain, be first placed in dilute solution and the
strength of this solution he gradually increased.
The combination of chromic acid compounds and chromic oxide salts is especially
to be recommended when it is wished to obtain leather of good weight.
For soft pliable upper leather I find it a very good method to tan the hides
at first in compounds of chromic acid and chromic oxide and then in a solution
of thiosulphate of chromium.
I find it a very good method to prepare this solution of thiosulphate of chromium
in the following way :-
I dissolve chrome-alum or chromic salts by heating in 6 to 10 times as much
water. If alum or sulphate of chromium is used I precipitate the sulphuric acid
of the chromium by chloride of barium, then I add an equivalent quantity of thio-
sulphate of sodium or instead of an equivalent quantity two or three equivalents
of sodium may be used.
The hides to be tanned may also be first tanned with alkaline salts of chromic
acid or chromic acid alone and then finished with chromic sulphite or chromic
thiosulphate or chromous oxide compounds. Also vice versa one may proceed by
first tanning in chromic sulphite or chromic thiosulphate and then finish in potassium
or sodium bichromate or chromic acid.
In place of chromic sulphite and thiosulphate, thiosulphate of iron, zinc,
manganese, aluminium, or the hydrosulphites of sodium, potassium, iron and zinc
may be used. The thiosulphates of these metals decompose, without addition of
acid, the chromic acid and the above mentioned chromic acid compounds; the

page_text: chromic acid is thereby reduced to chromic oxide or combines with the metallic
oxides with the result of precipitating metallic oxides in the fibres of the hide.
The hydrosulphurous acid salts (hydrosulphites of sodium, potassium, iron and
zinc,) are far more efficaceous than the metallic thiosulphates for treating hides
which have been previously treated with chromic acid compounds or chromic acid.
Even the alkaline salts of hydrosulphurous acid effect the reduction of the
chromic acid and its compounds without addition of acid which is not the case
with the alkaline thiosulphates.
The metallic salts of hydrosulphurous acid are much more efficaceous than the
alkaline salts of the latter. The metallic salts thereby deposit metallic oxide
which not only tans but also gives colour. The chromic and chromous oxide salts
in use in my process reduce without any addition of acid the chromic acid and
chromic acid compounds.
Should the thiosulphites of iron, zinc, magnesium, aluminium, or the salts of
hydrosulphurous acid or chromous oxide salts be used instead of thiosulphite and
sulphite of chromium, the previously tanned hides are brought also first into a
dilute solution of the salts.
Whether and how the above mentioned chromic acid, chromic and chromous
oxide compounds may preferably be combined with one another or preferably used
alone of course depends upon what quality of leather it is wished to produce
and the colour it is desired to be.
Compounds of chromic chromate, chromate sulphate of chromium, chromic
thiosulphate, chromic sulphite are taken up so easily and in such great quantity by
the fibres of the hide and are retained so well that they may for some kinds of
leather be used alone for tanning.
If it be wished to obtain a very complete tanning of the leather and good
weight the above named combinations are preferably used.
If it be wished to produce an especially hard and solid leather, hide tanned with
the above mentioned chromium compounds is treated with barium thiocyanate,
when by decomposition there is formed chromium thiocyanate and the corresponding
barium salt which for the most part is deposited on the fibres of the hide.
The tanned hides for upper leather or other light leather as soon as they come
out of the tan liquor should be well washed, greased and dressed according to the
known methods.
If it be wished to produce coloured or black leather, the hides are preferably
coloured or blackened before the greasing.
Hides intended for ordinary sole leather may not be washed but may be taken
out of the tan liquor dried and dressed in the usual way.
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. The process of tanning hides consisting in subjecting them to the action of a
solution containing chromic chromate.
2. The process of tanning hides consisting in subjecting them to the action of a
solution containing one of the chromate sulphates of chromium herein described.
3. The process of tanning hides consisting in subjecting them successively to
the action of a solution containing chromic chromate or one of the chromate
sulphates of chromium and a solution containing one of the chromic acid compounds
formerly employed.
4. The process of tanning hides consisting in subjecting them successively to
the action of a solution containing chromic chromate or one of the chromate
sulphates of chromium and a solution containing chromic, ferrous, aluminium zinc
or manganese thiosulphate.
5. The process of tanning hides consisting in subjecting them successively to the
action of a solution containing chromic chromate or one of the chromate sulphates

page_text: of chromium and a solution containing ferrous, zinc, manganese or sodium.
hydrosulphite..
6. The process of tanning hides consisting in subjecting them successively to the
action of a solution containing aluminium chromate alone or successively with a
solution containing aluminium chromate and a solution containing chromic acid'
or one of the alkaline compounds of chromic acid.
7. The process of tanning hides consisting in subjecting them to the action of a
solution containing chromic, ferrous, aluminium zinc or manganese thiosulphate
alone or successively with a solution containing chromic, ferrous, aluminium zinc
or manganese thiosulphate and a solution containing chromic acid or one of the
alkaline compounds of chromic acid.
8. The process of tanning hides consisting in subjecting them to the action of a
solution containing chromic sulphite alone or successively with a solution containing
chromic sulphite and a solution containing chromic acid or one of the alkaline
compounds of chromic acid.
9. The process of tanning hides consisting in subjecting them to the action of a
solution containing chromous chloride or sulphate alone or successively with a
solution containing chromous chloride or sulphate and a solution containing
chromic acid or one of the alkaline compounds of chromic acid.
10. The process of tanning hides consisting in subjecting them to the action of
a solution containing chromium thiocyanate.
11. The process of tanning hides consisting in subjecting them to the action of a
solution containing ferrous, zinc, manganese or sodium hydrosulphite alone or
successively with a solution containing ferrous zinc manganese or sodium
hydrosulphite and a solution containing chromic acid or one of the alkaline compounds.
of chromic acid.
Dated this 14th day of March 1894..