IMPROVEMENTS IN THE MANUFACTURE OF CHROMATE OF SODA AND CHROMIC ACID.
Year: 1881

page_text: PROVISIONAL SPECIFICATION left by Charles Denton Abel at the Office of
the Commissioners of Patents on the 1st December 1881. A communication
from abroad by Friedrich Carl Glaser of Berlin in the German Empire
Engineer.
CHARLES DENTON ABEL of No. 28 Southampton Buildings Chancery Lane
in the County of Middlesex "IMPROVEMENTS IN THE MANUFACTURE OF
CHROMATE OF SODA AND CHROMIC ACID.". [A communication from abroad by
Friedrich Carl Glaser of Berlin in the German Empire Engincer.]
In all cases where chromate of potash is used, it is chromic acid which enter>>
into the combinations, the potash playing in most cases an unimportant part,
excepting in the manufacture of chromate of alum.
The principal object of the present Invention is the substitution of soda in place
of the potash in this salt, as by the comparative cheapness of the latter a very
economical advantage is gained.
Up to the present time chromate of soda has not been produced on a practical
scale from chromate of iron, and the present Invention relates to such production
on a manufacturing. scale, whereby, on the assumption that the potash of the
chromate of potash only serves as medium for presenting the chromic acid in a
marketable form, that expensive substance is replaced by soda.
Chromate of soda is at present obtained in alizarine works from the lyes
containing chromium sulphate which are produced in the oxidation of the
anthracine. The precipitated chromic oxide is in this case mixed with lime, and
the mixture is oxidised in a reverberatory furnace and the chromate of lime
formed is treated with sulphate of soda. This constitutes therefore a regenerative
process.
According to the present Invention chromate of iron is employed for the
production of the chroinate of soda as follows: Chromate of iron, ground fine is
mixed with lime and carbonate of soda in suitable proportions and subjected to a
strongly oxidizing flame at a bright red heat until the mass shews no more
unconverted ore. By lixiviation with boiling water, with or without the addition
of soluble soda compounds, such as sodic carbonate or sulphate or caustic soda, the
chromate of soda is obtained as aqueous solution. Suitable proportions for the
mixture are 100 parts of ore, 100 to 150 parts of lime, and 40 to 70 parts of
carbonate of soda. The lime can be replaced by equivalent quantities of powdered

page_text: limestone or chalk, and the carbonate of soda by an equivalent quantity of caustic
soda or sulphate of soda.
By this means the neutral chromate is obtained.
If it be desired to obtain acid chromate, there is added before the lixiviation,
sulphuric or hydrochloric acid in any desired proportions.
According to another modification instead of employing the above described
mixture of soda and lime, finely divided carbonate of lime or caustic lime is mixed
in suitable proportions with the finely powdered chromate of iron, which mixture
is converted under the action of a strongly oxidising flame into chromate of lime,
and this is then converted into acid or neutral chromate of soda by treating it
with carbonate or sulphate of soda or caustic soda, or the chromate of lime is
treated with sulphuric or hydrochloric acid, and the chromic acid thus produced is
either introduced directly into commerce, or it is treated with carbonate or caustic
soda for conversion into acid or neutral chromate of soda.
In all the above described processes, both with the use of a mixture of lime and
soda compounds, as also with the use of a mixture of chromate of iron with lime
only, the last named substance, or the soda compounds, or both, can be partially or
entirely replaced by carbonate of magnesia, carbonate of strontia, or carbonate of
baryta, or by suitable mixtures of these substances.