IMPROVEMENTS IN OR APPLICABLE TO THE MANUFACTURE OR EXTRACTION OF TANNIN
Year: 1880

page_text: LETTERS PATENT to Walter Alfred Barlow, of 6, St. Paul's Churchyard,
London, Patent Agent and Engineer, for an Invention of "IMPROVEMENTS
IN OR APPLICABLE TO THE MANUFACTURE OR EXTRACTION OF TANNIN."
A communication from abroad by Paul Gondolo, of Paris, France.
PROVISIONAL SPECIFICATION left by the said Walter Alfred Barlow at the
Office of the Commissioners of Patents on the 16th April 1880.
WALTER ALFRED BARLOW, of 6, St. Paul's Churchyard, London, Patent Agent
and Engineer. "IMPROVEMENTS IN OR APPLICABLE TO THE MANUFACTURE OR
EXTRACTION OF TANNIN." A communication from abroad by Paul Gondolo, of
Paris, France.
This Invention relates to certain improvements upon Letters Patent, No. 1070,
A.D. 1879, wherein is claimed a new method of obtaining with vegetable matters,
of which the decoctions are of a strong color, extracts of tannin of a light yellow
color and very fluid. In working out this Invention some modifications have been
made in certain parts which assures the success of the Invention.
That process, as explained, comprises two operations which complete the process,
vis.
First. The extraction of the matter.
Second. The clarification of the decoction. In the precedent Invention above
referred to recourse is hind for extracting the tannin to acidulated water, in which
the vegetable matter is macerated. There is thus obtained a decoction whereof
the excess of acid is precipitated by means of an alkaline salt.
The liquid extracts furnished by this process are a little less strong in colour than
if non-acidulated water had been employed for producing the maceration, but they
nevertheless present a higher degree of color than will allow of their being employed
in the tanning of leathers. This coloring is still greater when, instead of employing
simply bark, recourse is had to woods themselves. It is therefore important in the
first operation to produce as complete a decolorisation as possible.
For this purpose, and according to this Invention, there is employed instead of
an acidulated water a water containing a certain proportion of a sulphite or a
bisulphite of any kind. In presence of the tannic acid the sulphite or bisulphite is
decomposed, and forms (in the case of the sulphite of soda, for example,) a tannate
of soda and of the sulphuric acid, which dissolves in the bath and operates as a
reducer upon
the coloring matters. This reaction produces a certain quantity of
sulphuric acid, which precipitates the salts of lime that may be in the liquor, and
thus neutralize their alkaline action on the tannin.
In this state the decoction contains tannate of soda, which is not right for tanning

page_text: purposes. This salt is reduced, and the sulphite or bisulphite which has not been
decomposed is eliminated by the sulphuric acid, which is introduced in sufficient
proportion to render the bath slightly acid.
The decoction thus obtained is notably of less color than that furnished by the
process which forms the subject of the above mentioned Patent; it is necessary,
nevertheless, to clarify it if it is desired to use it for tanning uncolored leathers.
This second operation is so much the more indispensable if the solutions are more
highly colored, which takes place when, instead of oak bark, for example, there is
employed higher colored barks or oak wood, chestnut, or other essence. The existing
processes of clarification present the double inconvenience of producing but an
incomplete decolorisation, and precipitating a considerable quantity of tannin.
An indispensable condition for obviating these inconveniences is that the
decolorizing matter must be intimately mixed in the bath, and that it operates at
the same time on every molecule which compose it.
It is impossible to obtain this result when an albumenous matter is added if
account is not taken of the conditions under which it will coagulate.
The process that has been devised permits the obtaining from liquid extracts of a
very highly clarified quality by employing a coagulent, blood for example, to which
preference is given.
a
The following is a description of the process:-
The liquid proceeding from the maceration, which is carried, as lias been described,
into a reservoir, is at such a temperature that the albumen would coagulate imme-
diately if blood was introduced at this moment. To avoid this effect the decoction
is made to flow into a second reservoir furnished in the interior with worm pipes,
over which a stream of cold water is passed, whereby the temperature is lowered
to about 45°, that is to say, below the point at which the albumen will coagulate.
The blood is then introduced, and becoming diffused in the liquid is intimately
mixed with it upon its being stirred. Steam is then passed through the worm and
tho temperature will be raised up to the point at which the albumen will coagulate,
but care is to be taken not to sensibly exceed this point, and the liquid is then left
to itself for a certain time.
The albumen coagulating decolorizes the decoction, however deep the shade may
be; it becomes charged with coloring matters, and is precipitated at the bottom of
the bath of liquid, which is now characterized by a remarkable clearness, and this
liquid, after filtration and subsequent concentration, yields extract of tannin of a
light yellow color, characterized by its fluidity, which is such that thick leather can
thereby be tanned in a few days.
On the contrary, as obtained by tho existing processos the extracts of tannin
have a syrup like consistency which prevents their penetrating the interior of the
leathers. They have further the considerable inconvenience of only serving for
tanning colored leathers by reason of their dark brown shade.
The fluidness and the decolorization which characterizes the extracts obtained
according to this Invention are the consequence of the new manipulations described
above, and which consist in cooling the decoction in such a manner as to carry it
below the point at which albumen coagulates, then to introduce the coagulent and
afterwards to raise the temperature up to the point at which the coagulation is
effected.
It has been observed that care must be taken not to raise the temperature of the
decoction higher than that at which albumen will coagulate, in fact, if it is con-
tinued to be heated it remains in suspension in the liquid, which remains thick and
of a deep color.
These diverse manipulations which constitute this Invention, and which are
intended to be claimed, allows of there being made tannic extracts of superior
quality by means of matters which hitherto had been considered as only giving
defective products, and thus cause a complete revolution in the art of tanning.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Walter Alfred Barlow in the Great Seal Patent Office on the
10th October 1880.
WALTER ALFRED BARLOW, of 6, St. Paul's Churchyard, London, Patent Agent
and Engineer.
"IMPROVEMENTS IN OR APPLICABLE TO THE MANUFACTURE OR
EXTRACTION OF TANNIN." A communication from abroad by Paul Gondolo, of
Paris, France.
This Invention relates to certain improvements upon Letters Patent, No. 1070,
A.D. 1879, wherein is claimed a new method of obtaining with vegetable matters,
of which the decoctions are of a strong color, extracts of tannin of a light yellow
color and very fluid. In working out this Invention some modifications have been
made in certain parts which assures the success of the Invention.
It is known that ordinarily the vegetable matter from which tannin is extracted
is treated by maceration either cold or more often hot.
In this process the matter is treated by maceration with this essential difference
that the water serving for tho maceration is slightly acidulated by an acid, by a
salt, or by an acid salt, provided it is not of such (a nature as to modify the
physical or chemical constitution of the tannin. Preferonce is given to sulphuric
acid, by which good results have been ascertained, its proportion varying in a
certain measure according to the more or less calcareous composition of the river
water or spring water employed for the extraction, but 9-25 grains of acid produces
the desired result.
The acid decoctions thus obtained are then treated by an alkali, but only in the
proportion strictly necessary to neutralise the acid remaining free. Either a caustic
or carbonated alkali or alkaline earth may be cimployed. For example, if the pro-
portion of acid indicated above has been used it has been ascertained that about
1543 grains (1 gramine) of carbonate of soda to 1.76 pint (one litre) of tho decoction
suffices to give the operation perfect success.
Morcover it is understood that if in the first operation a very great quantity of
acid has been employed, it is necessary for the saturation to increase in proportion
the quantity of alkali.
The tannic extract which is obtained after concentration by this method is much
superior to that which is ordinarily used in commerce, but there can be obtained,
as will be seen, a more complete result.
Different manufactures only making use of tannic extracts which are extremely
fluid and of slight color, there has been devised means whereby a product may be
obtained completely supplying their wants; for this the decoction is submitted soon
after the treatment by alkali to a third operation, viz., that of clarification.
This clarification is worked with the help of blood, albumen, glue or gluten, or
any other vegetable or animal substance which is able to tako up the natural
coloring of woods either by coagulation or by absorption. If a coagulent is
employed the decoction is brought to a lower temperature than that at which the
substanco employed coagulates, so that it is diffused through all the mass; the
temperature is then raised to the degree requisite to produce coagulation. The
decoction is then allowed to stand for about an hour; then it is drawn off, filtered,
and concentrated in the open air or in the vacuum from 3° to 45° Beaumé.
It will be seen that the process as above explained comprises two operations for
its completion, vis.
First. The extraction of the matter.
Second. The clarification of the decoction.
In carrying out the process above referred to recourse is had for extracting the
lulated to i which the vegetable matter is macerated There is

page_text: thus obtained a decoction, whereof the excess of acid is precipitated by means of
an alkaline salt.
The liquid extracts furnished by this process are a little less strong in color than
if non-acidulated water had been employed for producing the maceration, but they
nevertheless present a higher degree of color than will allow of their being employed
in the tanning of leathers. This coloring is still greater when instead of employing
simply bark recourse is had to woods themselves. It is therefore important in the
first operation to produce as complete a decolorization as possible.
For this purpose, and according to this Invention, there is employed instead of
an acidulated water a water containing a certain proportion of a sulphite or a
bisulphite of any kind. In presence of the tannic acid the sulphite or bisulphite
is decomposed and forms (in the case of the sulphite of soda for example) a tannate of
soda and some sulphurous acid, which dissolves in the bath and operates as a reducer
upon the coloring matters. This reaction produces a certain quantity of sulphuric
acid, which precipitates the salts of lime that may be in the liquor, and thus:
neutralise their alkaline action on the tannin.
In this state the decoction contains tannate of soda, which is not right for tanning
purposes. This salt is reduced, and the sulphite or bisulphite which has not been
decomposed is eliminated by the sulphuric acid, which is introduced in sufficient
proportion to render the bath slightly acid.
The decoction thus obtained is notably of less color than that furnished by the
process which forms the subject of the said Letters Patent before referred to; it is
necessary nevertheless to clarify it if it is desired to use it for tanning uncolored
leathers. This second operation is so much the more indispensable if the solutions
are more highly colored, which takes place when instead of oak bark, for examble,
there is employed higher colored barks, or oak wood, chestnut, or other essence. The
existing processes of clarification present the double inconvenience of producing
but an incomplete decolorization, and precipitating a considerable quantity of
tannin.
An indispensable condition for obviating these inconveniences is that the
decolorizing matter must be intimately mixed in the bath in order that it operates
at the same time on every molecule thereof.
It is impossible to obtain this result when an albumenous matter is added if
account is not taken of the conditions under which it will coagulate.
This improved process has been devised so as to obtain liquid extracts of a very
highly clarified quality by employing a coagulent, blood for example, to which
preference is given.
The following is a description of the said process :-
The liquid obtained from the maceration, which is carried, as has been described,
into a reservoir, is at such a temperature that the albumen would coagulate imme-
diately if blood was introduced at this moment. To avoid this effect the decoction
is made to flow into a second reservoir furnished in the interior with a serpentine-
pipe, through which a stream of cold water is passed; the temperature of the said
reservoir is thus lowered to about 45°, that is to say, below the point at which the
albumen will coagulate. The blood is then introduced, and becoming diffused in
the liquid is intimately mixed with it upon its being stirred. Steam is then passed
through the serpentine-pipe, and the temperature will be raised up to the point at
which the albumen will coagulate, but care is to be taken not to sensibly exceed
this point, and the liquid is then left to itself for a certain time.
The albumen coagulating decolorizes the decoction, however deep the shade may
be, and becomes charged with coloring matters, and is precipitated at the bottom of
the bath of liquid, which is now characterized by a remarkable clearness, and this
liquid, after filtration and subsequent concentration, yields extract of tannin of a
light yellow color, characterized by its fluidity, which is such that thick leather can
thereby be tanned in a few days. On the contrary, as obtained by the existing
processes, the extracts of tannin have a syrup like consistency which prevents their
penetrating the interior of the leathers. They have further the considerable

page_text: inconvenience of only serving for tanning colored leathers by reason of their dark
brown shade.
The fluidity and the decolorization which characterizes the extracts obtained
according to this Invention are the consequence of the new manipulations described
above, and which consist in cooling the decoction such a manner as to carry it
below the point at which albumen coagulates, then to introduce the coagulant, and
afterwards to raise the temperature up to the point at which the coagulation is
effected.
It has been observed that care must be taken not to raise the temperature of the
decoction higher than that at which albumen will coagulate; in fact if it is con-
tinued to be heated the coagulated albumen remains in suspension in the liquid,
which remains thick and of a deep color.
These diverse manipulations which constitute this Invention, and which are
intended to be claimed, allows of there being made tannic extracts of superior
quality by means of matters which hitherto had been considered as only giving
defective products, and thus cause a complete revolution in the art of tanning.
In order that the Invention may be well understood there is annexed hereto a
Sheet of Drawings, and the same is referred to by Figures and letters in the
following particular description:-
Fig. 1, A, B, C, D, E, aro wooden vats alike in size, or they may be made of any
convenient material, and they have a discharge cock 1 for the liquids; M is a
reservoir, into which the vats A, B, C, D, E, are emptied through the pipe 2, which
communicates with the pipes 1. Each of the vats is provided with a cock 3 so as
to be in communication with a steam pipe ; it is provided also with a blow-off-
cock 5. The cocks 1 and 3 are worked by means of a rod and handle 6. A plat-
form T is fixed on the side of the vats in order to make the work easy during the
operation.
All the vats A, B, C, D, E, may be emptied into the reservoir M through the
pipe 2, and also may be heated by means of steam carried through the pipe 4,
They are also in communication with a reservoir N through the pipes a and b.
which in addition to movable delivering pipes and nozzle c allows of pouring into
any of the vats as desired a quantity of the liquid contained in the said reservoir N.
The purpose of the pipe 7 terminated by similar nozzle and movable pipe is to
carry water into the vats.
P is a pump for the purpose of drawing the liquids from the reservoir M and
then forcing them into the reservoir N; R, R¹, are two reservoirs arranged in such
a way as to receive when required the liquids from the reservoir N. These
reservoirs communicate with a vat H of the same size as the vats A, B, C, D, E,
but provided inside with a serpentine-pipo S and a steam heater St. Cold water
may be carried into the serpentine pipe S through the pipe 10. The said vat H is
provided further with a floating decanter Z, which floats at the surface of the
liquid to suck it, and carries it to a filter t placed below (see Fig. 2). The said
filter t may be of any kind, but it is preferable to use a small cask filled with
wooden shavings, which have already been used.
The operation is conducted as follows:-
The vat A is charged with wooden shavings, then filled with water, to which
will be added 77.15 grains (5 grammes) of sulphite or bisulphite to each 2.20 lbs.
(1 kilogramme) of wood. The steam is then carried in through the cock 3, and
the mass is boiled for about an hour; the cock 3 must then be closed and the
cock 1 opened in order to carry the liquid into the reservoir M. The pump P then
draws the liquid and forces it into the reservoir N, from thence it is collected in
the reservoirs R and R', which serve for storing the liquids. A second operation
is then effected in the vat A with the same wooden shavings by introducing water
through the pipe 7, and as in the first operation the liquids resulting from this
operation are carried either into the reservoir R or R', the next vat B having been
meanwhile charged with shavings.
Then the third operation is to be effected by pouring water into the vat A and

page_text: forcing it by means of the pump P from the reservoirs M and N through the pipes
a and b into the vat B, from which latter the liquid is carried into the reservoirs
R and R¹.
The fourth operation is identical to the third one, and in the fifth operation the
only difference is that the liquid passes through the vat C before being carried to
the reservoirs R and R', and the sixth operation is identical to the fifth, and so
forth. It will be noticed that the operation is done twice upon fresh wood before
the liquids are carried into the reservoirs R and R'; moreover, the operation may
be carried out three times instead of twice upon the fresh wood, according to the
richness of it. Each of the 'vats participate in twelve operations, and then are
emptied and are charged anew with fresh wood.
In each of the vats the sulphite or bisulphite is added to the fresh wood in order
to obtain the reaction described in the said Letters Patent before referred to.
There is introduced into the reservoirs R and R' which contain the sufficiently
'concentrated liquids a quantity of sulphuric acid dosed in such a manner as to
reduce the tannate of soda, to climinate the sulphite not decomposed, and to render
the bath slightly acid.
The sulphuric acid may be introduced into the clarifying vat H, but it is to be
noticed that the decoction must not show more than 2° Benumé for the completo
'success of this system of clarification.
The decoction contained in the reservoir R and R' is carried into the special
vat H where the clarification is to be operated. As however the temperature of
the said decoction generally rather high it is brought to a lower degree than
that at which the albumenous or gelatinous matters coagulate, it will not be
necessary to cool the said liquids in the vat H.
When it is ascertained that the temperature of the liquids is under 40° then the
albuminous or gelatinous matters (blood by preference) will be mixed by means of
stirring, and the temperature of the mass will be raised by means of a heater S¹ up
to the degree at which albumen or gelatine coagulates. The cooling matters are
thus thrown down and precipitated at the bottom of the bath, but this result may
'only be obtained, as it has been already said, if the density of the bath does not
exceed 2° Beaumé on account of the very slight difference between the density of
the liquid and the density of the precipitate.
As soon as the leposit is effected the liquid will be decanted by means of the
floating decanter Z, and then the liquid will be filtered by passing through
the small caskt (Fig. 2), from whence it will escape into the cistern a, thus the
operation is terminated and the liquids obtained may be used for the purpose of
tanning, unless they are to be conveyed away, in which case it is convenient to
concentrate them by evaporation in order to transform them into extracts.
As will be seen the process is characterized by the following special features:-
1st. Several vats for decoction arranged in such a manner that the extraction of
tannin is made methodically on wood reduced to shavings.
2nd. A reservoir for the reception of liquids coming from the vats.
3rd. A pump either for the purpose of forcing the liquids into the reservoir or
for sending water into the vats.
4th. One or more reservoirs or vats for the purpose of receiving liquids sufficiently
-rich in tannin.
5th. A clarifying vat so arranged that the liquids contained therein may be
cooled or heated in order to produce the coagulation of albumen or gelatine, and
thus the precipitating of coloring matter.
Lastly. A system of decantation and filtration of the clarified liquids.
All the several parts of the apparatus are connected by means of convenient pipes
and 'cocks.
Having now described the nature and particulars of the said Invention I
claim;―
:
1st. The process of extraction of tannin combined with the clarification, as above
.described.

page_text: 2nd. The method of clarifying by the use of blood, taking care to lower the
temperature of the decoction under the degree at which the albuinen coagulates,
and then to raise it to that degree the precipitation of the said albumen.
3rd. The apparatus above described and shown in the annexed Sheet of Drawings
and for purpose of effecting the methodical extraction of tannin, and the clarifica-
tion thereof by means of blood.
In witness whereof, I, the said Walter Alfred Barlow, have hereunto set my
hand and seal, this Sixteenth day of October, in the year of our Lord One
thousand eight hundred and eighty.
WALTER A. BARLOW. (L.S.)