Containing Tannin.
Year: 1884

page_text: Containing Tannin.
I, JULES DOUTRELEAU, of Graville près le Havre, in the republic of France,
Gentleman, do hereby declare the nature of said invention for PROCESS FOR
DISCOLOURING AND PURIFYING VEGETABLE EXTRACTS CONTAINING TANNIN, to be
as follows:-
My invention has for its object to separate the greatest part of colouring
matters from tanning liquors of any specific weight, in order to use the latter in
tanning, dyeing and printing.
The process is applicable to all vegetable materials containing tannin, such as
various kinds of wood and bark, leaves, roots, husks, and fruits. The liquid
extract of the materials containing tannin is mixed with a sulphite or hyposulphite,
preferably hyposulphite of alumina, or with substances adapted to produce these
salts, in proportions depending on the quantities of colouring matters contained in
the said extract. The tanning liquor is now heated, in order to split up the
hyposulphite of alumina or analogous hyposulphites into hyposulphurous acid,
which destroys colour, and alumina, which forms with colouring mattor a precipitate
of insoluble lac (lake).
The hyposulphurous acid is oxidised, at the expense of the colouring matters, so
as to form sulphuric acid, which combines with the lime (contained in all natural
tanning substances), so as to form a precipitate of gypsum or sulphate of lime.
In this manner the hyposulphite employed is naturally eliminated without
leaving any residue in the tanning liquor.
The liquor is then filtered or decanted, after which it may be immediately used
for tanning hides, or it may be converted into dry liquid extracts by concentration
in the ordinary manner.
The quantity of the salt to be used varies according to the nature of the tanning
liquor to be discoloured.
A suitable proportion is for instance: 1 gramme of hyposulphite for 1 litre of a
decoction of oak bark or chestnut-wood at 2° Beaumé,

page_text: Process for Discolouring and Purifying Vegetable Extracts
Containing Tannin.
I, JULES DOUTRELEAU, of Graville near Havre, France, Manufacturer, do hereby
declare the nature of my invention for PROCESS FOR DISCOLOURING AND PURIFYING
VEGETABLE EXTRACTS CONTAINING TANNIN, and in what manner the same is to be
performed, to be particularly described and ascertained in and by the following
statement:-
5
My invention has for its object to separate the greatest part of colouring
matters from tanning liquors of any specific gravity, in order to use the latter in
tanning, dyeing and printing. The process is applicable to all vegetable materials,
containing tannin, such as various kinds of wood and bark, leaves, roots, pods and
fruits. The liquid extract of the materials, containing tannin, is mixed with a 1
sulphite or hyposulphite, preferably hyposulphite of alumina, or with substances,
capable of producing these salts, in proportions, depending on the quantities of
colouring matters, contained in the said extract. The tanning liquor is now heated,
in order to split up the hyposulphite of alumina, or analogous byposulphites, into
hyposulphurous acid, which destroys colour, and alumina, which forms with the 1
colouring matter an insoluble precipitate.
The byposulphurous acid is oxidised at the expense of the colouring matters, so
as to form sulphuric acid, which combines with the lime (contained in all natural
tanning substances), so as to form a precipitate of gypsum or sulphate of lime.
In this manner, the hyposulphite employed is naturally eliminated without
leaving any residue in the tanning liquor.
The liquor is then filtered or decanted, after which it may be immediately used
for tanning hides, or it may be converted into dry or liquid extracts by
concentration in the ordinary manner.
The quantity of the salt to be used varies according to the nature of the tanning
liquor to be discoloured.
A suitable proportion is for instance:
1 gramme of hyposulphite for 1 litro of a decoction of oak bark, or chestnut-
wood at 2° Beaumé.
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.) Discolouring and purifying tanning liquors, which are employed either
directly for tanning or dyeing, or for the manufacture of extracts.
2.) Discolouring and purifying tanning liquors by the addition of sulphites or
byposulphites, or of compounds capable of forming sulphites or hyposulphites, and
heating the liquors mixed with the said salts or compounds.