Improvements in the Process of Mordanting Wool and other Animal Fibre.
Year: 1896

page_text: PROVISIONAL SPECIFICATION.
Improvements in the Process of Mordanting Wool and other
Animal Fibre.
I, ALEXANDER MELVILLE CLARK of the Firm of A. M. & Wm. Clark of 53,
Chancery Lane in the County of Middlesex, Fellow of the Chartered Institute of
Patent Agents; do hereby declare the nature of this Invention (a communication
to me by C. H. BOEHRINGER SOHN of Niederingelheim-on-the-Rhine Chemical
Works, Germany;) to be as follows:--
The mordanting of wool by chromates in conjunction with lactic acid in lieu
of tartar or of oxalic acid has been known for some time but the results hitherto
obtained have been very variable and for the most part not in favour of the use of
lactic acid.
By the process of the present Invention the following new results have been
obtained: the mordanting lye is completely exhausted (i.e. all the chromium is
precipitated) and the wool is mordanted a clear green shade and in the most suit-
able manner for the subsequent dyeing.
In all previous instances lactic acid has been employed in almost precisely the
same manner as tartar and oxalic acid, no regard being had to the special chemical
qualities of the new acid, whereas my discoveries relating to this subject have
shewn that lactic acid acts quite differently in presence of chromates to the old
mordants.
In the first place lactic acid is much more easily attacked by the oxide of
chromium than the other agents, which decompose at ordinary temperature,
whilst tartar and oxalic acid require boiling heat.
I have further found that the process of oxidation may easily be conducted
in such manner that lactic acid is decomposed into aldehyde and carlsonie acid,
all chromate being at the same time reduced to oxide of chromium and deposited
as a green precipitate.
This for instance is the case if the following mixture is slightly heated and
afterwards boiled for about an hour:-
5
grammes lactic acid 50 %
3 grammes bichromate of potash
0,5 grammes sulphuric acid"
dissolved in 200 cubic centimetres of water. But an excess of bichromate or au
excess of acids produces another result; in the first case the liquid remains yellow
from the unaltered bichromates, and in the second case the oxide of chromium
may be dissolved again by these acids in the form of green salts. Tartar and
oxalic acid however never reduce all the bichromate and can never precipitate
oxide of chromium, the excess of acids always maintaining the reduced products
lissolved as a yellow solution of a more or less greenish shade.
This process of oxidation causing the complete reduction of all the bichromate
may easily be applied with a success not obtained hitherto in mordanting. wool;

page_text: For instance for a perfect result the process may be worked in the following
manner:-
100 kilos of wool cleaned as usual and previously moistened are treated for
half an hour at 160° Fahrenheit, in a bath of 2000 litres of water containing:-
2,65 kilos lactic acid 50 %
1,35 kilos bichromate of potash
0,90 kilos sulphuric acid
(A)
being slowly heated to boiling point and thus continuing for half an hour. The
wool appearing yellow at the beginning slowly turns green whilst the liquid at
first appearing yellow is quite colourless at the end of the operation.
This splendid result however is only obtained if the above conditions are ob-
served; neither an excess of bichromates nor of acids can yield the same result;
on the contrary in any other way very bad results are obtained.
This is the case for instance when an excess of bichromate is used for mor-
danting, say:-
(B) 3 kalos bichromate of potash
2,5 kilos lactic acid
a proportion mostly used thus far and corresponding with the tartar method.
The wool so mordanted is quite yellowish and the liquid also of a decided
yellow. The wool and the liquid still appear yellowish, but less, when the
propor-
tions first above indicated (A) are employed, omitting the sulphuric acid, thus:-
(C) 2,65 kilos lactic acid
1,35 kilos bichromate of potash
The desired perfect result yielded by the new operation can therefore only be
obtained if there is neither an excess of bichromate nor of acids, the latter inain-
taining a part of the oxide of chromium dissolved in the liquid which then appears
greenish and acts less on the wool.
It is also necessary that all trioxide of chromium be freed from the salt by the
acids. For the last mentioned purpose it is of course best and most profitable to
use sulphuric acid of which a small quantity acts just as strongly as a much
greater quantity of expensive organic acids (0,9 kilos sulphuric acid being equal
to 2,5 kilos lactic acid) and the lactic acid already employed being quite sufficient
for the complete reduction of the trioxide of chromium.
Other mineral acids such as muriatic acid and nitric acid are not profitable
hecause they may cause additional reactions on the wool and the mordants in
contrast to sulphuric acid.
The advantages resulting from the new mordanting process are:-
1. A great saving of chrome:
2. The shades are purer and faster in every respect to scouring, milling,
light, and air.
As it is known the combinations of pure oxide of chromium with dye-stuffs
are superior in every respect to combinations of the latter with chromates and
intermediate products thereof both of which are to be found on wool mordanted
yellowish. These intermediate products may also cause alterations of some
colours, log-wood colour for instance soon becomes green in this case.
3. The fibre remains much softer and more brilliant and is less spoiled than
in other cases.
The wool is only charged with pure oxide of chromium and only with the
quantity of mordant necessary for dyeing, without any other useless products, and
the duration of the boiling is less than in other cases.
4. The process is easily controlled and great regularity of the shades may
be obtained.
The completion of the operation is easily recognized as the liquid is quite de-
f

page_text: colourized by the complete exhaustion of the mordauting lye. The wool is always
mordanted quite regularly and in the same degree whereas in other processes
where the mordanting lyes are not exhausted the duration of the process and the
attenuation of the bath influence the result.
By the new mordanting operation the necessity for the difficult and trouble-
some correction of the shades, particularly in dyeing with alizarines, may be
avoided.
A. M. & WM. CLARK,
Chartered Patent Agents,
53 Chancery Lane,
London.
Improvements in the Process of Mordanting Wool and other
Animal Fibre.
I, ALEXANDER MELVILLE CLARK of the Firm of A. M. & Wm. Clark of 53,
Chancery Lane in the County of Middlesex, l'ellow of the Chartered Institute of
Patent Agents; do hereby declare the nature of this Invention (a communication
to me by C. H. BOEHRINGER SOHN of Niederingelheim-on-the-Rhine Chemical
Works, Germany) and in what manner the same is to be performed to be par-
ticularly described and ascertained in and by the following statement:-
The mordanting of wool by chromates in conjunction with lactic acid in lien
of tartar or of oxalic acid has been known for some time but the results hitherto
obtained have been very variable and for the most part not in favour of the use of
lactic acid.
By the process of the present Invention the mordanting lye is completely ex-
hausted (i.e. all the chromium is precipitated) and the wool is mordanted a clear
green shade and in the most suitable manner for the subsequent dyeing.
In all previous instances lactic acid has been employed in almost precisely the
same manner as tartar and oxalic acid, no regard being had to its special chemical
qualities, whereas lactic acid acts quite differently in presence of chromates to
the old mordants.
In the first place lactic acid is much more easily attacked by the oxide of
chromium than the other agents, which decompose at ordinary temperature,
whilst tartar and oxalic acid require boiling heat.
It has further been found that the process of oxidation may easily be conducted
in such manner that lactic acid is decomposed into aldehyde and carbonic acid,
all chromate being at the same time reduced to oxide of chromium and deposited
as a green precipitate.
This for instance is the case if the following mixture is slightly heated and
afterwards boiled for about an hour:-
5 grammes lactic acid 50%
3
grammes bichromate of potash
0,5 grammes sulphuric acid
dissolved in 200 cubic centimetres of water. But an excess of bichromate or an
1

page_text: The wool is only charged with pure oxide of chromium and only with tho
quantity of mordant necessary for dyeing, without any other useless products, aud
the duration of the boiling is less than in other cases.
4. The process is easily controlled and great regularity of the shades may
be obtained.
The completion of the operation is easily recognized as the liquid is quite de-
colourized by the complete exhaustion of the mordanting lye. The wool is always
mordanted quite regularly and in the same degree whereas in other processes
where the mordanting lyes are not exhausted the duration of the process and the
attenuation of the bath influence the result.
By the new mordanting operation the necessity for the difficult and trouble-
Somo correction of the shades, particularly in dyeing with alizarines, may be
some
avoided.
5. It has been found that the exhausted lye of the mordanting operation
may be used as the bath for the subsequent dyeing thereby avoiding transferring
from one tank to another. The little remaining acid must be neutralized.
Having now particularly described and ascertained the nature of the said In-
vention and in what manner the same is to be performed I declare that what I
claim is:-
The improvement in the process of mordauting wool and other animal fibre,
which consists in the use of lactic acid or a salt of lactic acid, such as potassium
lactate, in conjunction with a bichromate such as potassium bichromate and a
strong acid, preferably a mineral acid, such as sulphuric acid, and in substan-
tially the proportions herein specified.
100%