IMPROVEMENTS IN THE MANUFACTURE AND PRODUCTION OF THE CHROMATES AND THE BICHROMATES OF POTASH AND OF SODA
Year: 1862

page_text: PROVISIONAL SPECIFICATION left by-Charles Denton Abel at the Office
of the Commissioners of Patents, with his Petition, on the 17th April
1862. A communication from abroad by Louis Alexandre Taillandier,
Chemist, of Argenteuil, in the Empire of France.
I, CHARLES DENTON ABEL, of No. 20, Southampton Buildings, Chancery
Lane, in the County of Middlesex, Patent Agent, do hereby declare the
nature of the said Invention for "IMPROVEMENTS IN THE MANUFACTURE AND
PRODUCTION OF THE CHROMATES AND THE BICHROMATES OF POTASH AND OF SODA,"
to be as follows:-
This Invention consists in substituting sulphate of potash and sulphate of
soda for the carbonates and nitrates of these bases, as employed at present in
the manufacture respectively of the bichromate of potash and of the bichromate
of soda.
In the manufacture of the bichromate of potash I operate in the following
manner-The ore known as chrome iron ore is first reduced to an almost
impalpable powder, this is then intimately mixed with sulphate of potash, and
with caustic lime or carbonate of lime in proportions, varying according to the
proportion of oxide of chromium contained in the ore. If, for instance, the
ore should contain thirty per cent. the mixture should consist of one hundred
parts by weight of the ore, forty parts by weight of sulphate of potash, and
one hundred parts by weight of carbonate of lime or of caustic lime. This
mixture is then thrown on the bed of a reverberatory furnace, upon which it
is spread in a layer of from three-quarters of an inch to an inch and a quarter

page_text: in thickness, and it is then maintained at a red heat, suitable apertures and
arrangements being provided in the furnace so that a highly oxydizing effect
may be produced on the mixture to be operated on in the furnace. By this
operation the sulphuric acid of the sulphate of potash will combine with its
equivalent of lime to form sulphate of lime, and the potash thus liberated
combines with the chromic acid (which is formed by the oxydation produced
under the influence of the excess of lime or carbonate of lime employed, and
the presence of atmospheric air,) to form chromate of potash. When this
operation is completed the mass is withdrawn from the furnace, and the soluble
chromates formed are dissolved in water, the weak liquors from the final
washings are employed for the solution of the soluble chromates from fresh
materials; the stronger solutions from the first operations are to be concen-
trated. The concentrated solution is then placed in a leaden vessel, and a
sufficient amount of sulphuric acid is added as may be requisite to combine
with one half of the potash of the neutral chromate contained in solution.
This solution is heated and is finally placed in crystallizing pans and is allowed
to cool gradually. The bichromate of potash will crystallize out, and the
sulphate of potash produced by the before-mentioned addition of sulphuric
acid is again employed in the production of chromates of potash by the process
as above described.
In the manufacture of bichromate of soda, I employ precisely the same
process as herein-before described, simply substituting sulphate for soda for
sulphate of potash.