Improvements in or relating to the Tanning and Treatment of Leather and Skins.
Year: 1899

page_text: Date of Application, 29th June, 1899
Complete Specification Left, 27th Mar., 1900-Accepted, 29th June, 1900
Improvements in or relating to the Tanning and Treatment of
Leather and Skins.
A communication from PIERRE AUGUSTE DENIS PROST and ANATOLE GODARD,
both of 39, Rue de la Villette, Lyons, in, the Republic of France.
I, ALFRED JULIUS BOULT, of 111, Hatton Garden, in the County of London,
Chartered Patent Agent, do hereby declare the nature of this invention to be
as follows:-
This invention relates to the tanning and treatment of leather and skins and
has for its object to facilitate the process of tanning and to enable a better product
to be obtained than hitherto.
According to this invention the skins, after being deprived of the hair and
removed from the "soaks" are treated with a solution of a metallic salt which
opens the pores of the skin, and deposits a salt in the skin amongst the fibres
tanning it in an improper manner owing to this salt being hygroscopic. The
skins are now, after drying, immersed in a solution containing a salt which will
combine with and fix the salt deposited in the skin forming an insoluble precipi-
tate, and at the same time completing the tanning process.
The solution which is preferably employed for the first bath is composed of
chloride of sodium and an acid such as sulphuric acid which combine to form
acid sulphate of soda. If desired the ordinary commercial acid sulphate of soda
may be used but it is preferable to make up the solution directly with chloride of
sodium and sulphuric acid. A proportion of tanning or other liquid may be
added to give colour to the skins. Spent bark is preferably placed between the
hides in the tank containing the sulphate solution, this arrangement ensuring a
better distribution of the solution throughout the hides. If colour is desired, new
bark may be used.
The second or fixing bath is composed of a solution of chloride of barium or
nitrate of baryta which with the sulphate of soda forms an insoluble sulphate of
baryta in the skins, a certain amount of tanning or other colouring liquid being
preferably added, or the skins laid down between layers of new bark which when
wet with the solution colours them.
If a chrome salt has been employed in whole or in part for the tanning it is
advisable in the second bath to reduce it by replacing a part of the chloride of
barium or nitrate of baryta by hypo-sulphite of soda or some other similar salt.
If the colouring matter is omitted, as the chemicals employed in forming the
solutions are themselves colourless the skins when treated will be white.
It is advisable to provide some means of agitating the solutions or the hides in
the solutions though this may not be necessary where the skins are laid down
with bark between them as described above.
On removing the skins from the first bath they are hung up to dry, and when
nearly dry they are "opened" by rolling on a table with an arm board, pommel or
similar tool with the object of rendering them more pliable and ready to absorb
the solution in the second bath into which they are now placed.
In certain cases where leather is to be employed for belting harness soles and

page_text: other purposes, after they have been treated in baths as above described and dried
they are caused to absorb copaline, tar or resin dissolved in alcohol or other
resiniferous alcoholic solutions with or without wax or other fatty or greasy
substances, which may be added to the solution if suppleness is required. When
the skins are saturated with these substances they are dried in such a way that
the alcohol which distils off can be recovered, any known method for this purpose
being employed..
In certain cases the leather is caused to absorb a solution of bichromated
gelatine or a solution of bichromate of potash, which is afterwards fixed and
reduced by hypo-sulphite of soda.
The proportions of the chemicals employed in the composition of the various
solutions may of course be varied in accordance with requirements.
Hotel 11: ORIL
T 1000
BOULT & WADE,
Agents for the Applicant.
.
Improvements in or relating to the Tanning and Treatment of
Leather and Skins.
A communication from PIERRE AUGUSTE DENIS PROST and ANATOLE GODARD,
both of 39, Rue de la Villette, Lyons, in the Republic of France.
I, ALFRED JULIUS BOULT, of 111, Hatton Garden, in the County of London,
Chartered Patent Agent, 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 the tanning and treatment of leather and skins and
has for its object to facilitate the process of tanning and to enable a better product
to be obtained than hitherto,
According to this invention the skins, after being deprived of the hair and
removed from the "soaks " are treated with a solution of a metallic salt which
opens the pores of the skin, and deposits a salt in the skin amongst the fibres
tanning it in an improper manner owing to this salt being hygroscopic. The
skins are now, after drying - immersed in a solution containing a salt which will
combine with and fix the salt deposited in the skin forming an insoluble precipi-
tate, and at the same time completing the tanning process.
The solution which is preferably employed for the first bath is composed of
chloride of sodium and an acid such as sulphuric acid which combine to form
acid sulphate of soda. If desired the ordinary commercial acid sulphate of soda
may be used but it is preferable to make up the solution directly with chloride of
sodium and sulphuric acid. A proportion of tanning or other liquid may be
added to give colour to the skins. Spent bark is preferably placed between the
hides in the tank containing the sulphate solution, this arrangement ensuring a
better distribution of the solution throughout the hides. If colour is desired, new
bark may be used.
The second or fixing bath is composed of a solution of chloride of barium or
nitrate of baryta which with the sulphate of soda forms an insoluble sulphate of
haryta in the skins, a certain amount of tanning or other colouring liquid being
preferably added, or the skins laid down between layers of new bark which when
wet with the solution colours them.

page_text: If a chrome salt has been employed in whole or in part for the tanning it is
sometimes advisable in the second bath to reduce it by replacing a part of the
chloride of barium or nitrate of baryta by hypo-sulphite of soda or some other
similar salt.
If the colouring matter is omitted, as the chemicals employed in forming the
solutions are themselves colourless the skins when treated will be white.
It is advisable to provide some means of agitating the solutions or the hides in
the solutions though this may not be necessary where the skins are laid down
with bark between them as described above.
On removing the skins from the first bath they are hung up to dry, and when
nearly dry they are opened" by rolling on a table with an arm board, pommel or
similar tool with the object of rendering them more pliable and ready to absorb
the solution in the second bath into which they are now placed.
In certain cases where leather is to be employed for belting harness soles and
other purposes, after they have been treated in baths as above described and dried
they are caused to absorb copaline, tar or resin dissolved in alcohol or other
resiniferous alcoholic solutions with or without wax or other fatty or greasy
substances, which may be added to the solution if suppleness is required. When
the skins are saturated with these substances they are dried in such a way that
the alcohol which distils off can be recovered, any known method for this purpose
being employed.
In certain cases the leather is caused to absorb a solution of bichromated
gelatine or a solution of bichromate of potash, which is afterwards fixed and
reduced by hypo-sulphite of soda.
The proportions of the chemicals employed in the composition of the various
solutions may of course be varied in accordance with requirements.
To tan, say 300 kilos of raw hide 500 kilos of the liquid are used at a tempera-
ture of from 25 to 30 Centigrade. The composition of the tanning liquids varies
according to the list following hereunder. The hides are tanned in tubs, tuns
or the like, kept in motion and are kept there for 3 to 6 hours, in the case of
sheep skins, 12 to 15 hours in the case of calf-skins, while the hides or larger
animals are kept in the lye for 18 to 24 hours.

page_text: ATIOS
N.B. In this bath the skins remain from 15 to 60 minutes according to their
thickness.
No. 3. COLOURED TANNING SUNK THROUGH THE WHOLE THICKNESS OF THE SKINS.
FIRST BATH.
Good vegetable tanning lye
Sodium chloride
Sulphuric acid
N.B. Duration of bath as before.
SECOND BATH.
500 litres.
50 kilos.
10 kilos.
After leaving the first bath, the hides are placed into tubs between layers
of bark, the height of which corresponds with the thickness of the skins, so as to
vield sufficient colouring matter to tan them. After the whole of the hides
have thus been imbedded and the last covered with an especially thick layer
of bark, the whole-skins and bark-is sprayed over with bark lye of medium
strength in which has, previously, been dissolved from 8 to 10 p.c. of barium
chloride or baryum nitrate.
In this condition the skins are left in the tubs until they are tanned right
through, which will be the case in a few days with sheep skins, 15 days with calf-
skins and a mouth with the hides of larger animals.
Instead of imbedding the skins in the manner described in a tub, the action
may be quickened, by placing them thus into a fulling fub or any vessel kept in
movement.

page_text: On occasion if a chrome salt has been used in the first bath in the proportion
of 500 grammes to 100 litres of sodium sulphate solution, these salts may be
reduced by employing in the second bath only one half the indicated weight
of baryta salt, replacing the other half by an equal weight of sodium hypo-
sulphite. It may however be more economical not to employ the latter but use
only a baryta salt as above.
Barium chloride or nitrate -
40 KHOS.
Vegetable or mineral colouring matter: in sufficient quantity to augment the
colouring, should this be required. In this bath the skins are left from 15 to
60 minutes, to transform the sodium sulphate contained in the fibres and pores
of the skins, into barium sulphate which is insoluble, absolutely stable and serves
to preserve the leather.
When it is required to obtain a firm and resisting leather, such as will serve
as sole-leather, the skins, after having been tanned by any means, are allowed
to dry, after which they are roughened on a gripper, so as to open the pores and,
thereby, enable them to easily absorb quickly and thoroughly a light solution
of chromated gelatine. The leather having been saturated with it, the excess of
it is removed by pressure, and the hides exposed to light and air for the purpose
of drying and transforming the chrome into oxide in which state it renders the
gelatine insoluble.
The chromated gelatine solution is composed as follows:
Water
Dry gelatine
Chromic acid or bichromate of potassium
Glycerine or molasses
100 parts.
5 to 10
"
1 to 2
"
1 part.
Having now particularly described and ascertained the nature of this said
invention as communicated to me by my foreign correspondent, and in what
manner the same is to be performed, I declare that what I claim is :-
-
1. A means of tanning skins after depilation which consists of a first operation
in a bath containing for economy a solution of a metallic salt with tanning
properties, but preferably chloride of sodium and sulphuric acid dissolved in a
coloured or uncoloured, tanning juice or liquor, or in a bath containing acid
5 sulphate of soda dissolved in water as described, and then of a second operation
in a coloured or colourless tanning liquid which transforms part of the salt
deposited during the first operation into an insoluble salt and fixes it in the pores
and fibres while the other part of the first salt is dissolved and replaced by the
tanning elements.
0 2. A means of directly colouring the skins by adding to the tanning baths the
colouring matter perded to obtain the required shade.

page_text: 3. A means of rendering skins impermeable by making them absorb, to the
point of saturation, resiniferous alcohol solutions or metallic salts which are
fixed and finally reduced by a second operation as described.
Dated this 27th day of March 1900.
BOULT, WADE & KILBURN,
Agents for the Applicant.