IMPROVEMENTS IN THE MANUFACTURE OF CHROMATES AND BICHROMATES
Year: 1885

page_text: Bichromates.
I, WILLIAM JAMES CHRYSTAL of 7 Park Circus, Glasgow, Lanarkshire, Fellow
of the Chemical Society, do hereby declare the nature of my Invention for
IMPROVEMENTS IN THE MANUFACTURE OF CHROMATES AND BICHROMATES," to be
as follows:-
"
My Invention has for its object the successful manufacture of chromates and
bichromates of potash and ammonia from the chromate or bichromate of soda.
I take a solution of chromate or Bichromate of Soda, and decompose it either
hot or cold with sulphate of Potash or sulphate of Ammonia either in the solid form
or in solution by direct action according to the equations :--
a) Na, Cr O + K₂ SO₁ =
(a) Naz Cro; + (NH₂ 50%
4
-
K₂ Cr O + Na SO
== (NH) Cr O + Na。 SO
(a) Na. Cr. O, + K₂ SO₂ = K, Cr₂ O7 + Na₂ SO,
7
b) Na₂ Cr₂ O, + (NH₁)₂ SO₁ = (NH), Cr, O, + Na, SO..
7
Equations 1 result in the production of (a) chromate of Potash and sulphate of
soda, and (b) chromate of Ammonia and sulphate of soda. These chromates
I separate from the sulphate of soda either by concentration and salting or by
crystallisation. The chromate of Potash or the chromate of ammonia so produced
may be converted into the corresponding Bichromate by the well known method.
Equations 2 result in the production of (a) Bichromate of Potash and sulphate of
soda, and (b) Bichromate of Ammonia and sulphate of soda. These Bichromates
I separate from the sulphate of soda either by concentration and salting or by
crystallisation.
The above equations represent equivalent quantities. In practice however the
quantities may be varied, either more or less sulphate of Potash and sulphate of
Ammonia being used.

page_text: Improvements in the Manufacture of Chromates and
Bi-chromates.
I, WILLIAM JAMES CHRYSTAL of 7 West George Street, in the City of Glasgow,
Fellow of the Chemical Society, do hereby declare the nature of this invention
and in what manner the same is to be performed to be particularly described and
ascertained in and by the following statement :-—
My invention has for its object the successful manufacture of chromates and
bi-chromates of potash and ammonia from the chromate or bi-chromate of soda.
For the manufacture of the chromates of potash and ammonia I employ a
solution of chromate of soda obtained preferably by furnacing chrome ore with a
'soda salt and lime and lixiviating the frit with an acidified solution of a soda salt in
the manner described in the Specification of my Letters Patent No 4028 of 1884,
and I treat the crude solution so obtained before, during, or after concentration
with sulphate of potash or sulphate of ammonia thereby converting the chromate
of soda into chromate of potash and sulphate of soda or into chromate of ammonia
and sulphate of soda according to the following equations, viz;.
Na, Cr O, + K, SO₁ = K₂ Cг O₁ + Na, SO
Na, CrO4 + (NH₁), SO. = (NH) Cr O₁ + Na, SO.
I then separate the chromate from the sulphate of soda either by concentrating
and salting or by crystallization, making use of their different solubilities at
different temperatures for the successful separation or I may separate the sulphate
of soda partly by concentration and fishing and partly by subsequent partial
cooling leaving the chromate in solution.
For the manufacture of the bichromates of potash and ammonia I may proceed
in either of two ways. (1) I may prepare the chromates of potash and ammonia in
the manner above described and convert them into the corresponding bichromates
by the addition of a suitable acid. Or (2) I may employ a solution of bichromate
of soda obtained as described in the Specification of my Letters Patent No 4028
of 1884 and treat it with sulphate of potash or sulphate of ammonia to convert
the bichromate of soda into bichromate of potash and sulphate of soda or
into bichromate of ammonia and sulphate of soda according to the following
equations viz.
Na, Cr, O + K, SO₁ = K, Cr, O, + Na, SO
Na, Cr₂ 07 + (NH₁), SO¿ = (NH). Cr, O7 + Na, SO.
I then separate the bichromate from the sulphate of soda either by concentrating
and salting or by crystallisation. In the latter case I prefer to allow the bichromate
to crystallise out on cooling a hot and nearly saturated solution, the sulphate. of
soda being left in solution.
The above equations represent equivalent quantities. In practice however the
quantities may be varied, either more or less sulphate of potash or sulphate of
ammonia being used.

page_text: 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.) The manufacture of chromato of potash by treating a solution of chromate
of soda with sulphate of potash and eliminating the sulphate of soda thereby
formed, substantially as herein set forth.
(2.) The manufacture of chromate of ammonia by treating a solution of chromate
of soda with sulphate of ammonia and eliminating the sulphate of soda thereby
formed, substantially as herein set forth.
(3.) The manufacture of bichromate of potash by treating a solution of chromate
of soda with sulphate of potash, eliminating the sulphate of soda and adding a
suitable acid to convert the chromate of potash into the bichromate, substantially
as herein set forth.
(4.) The manufacture of bichromate of ammonia by treating a solution of
chromate of soda with sulphate of ammonia, eliminating the sulphate of soda, and
adding a suitable acid to convert the chromate of ammonia into the bichromate,
substantially as herein set forth.
(5.) The manufacture of bichromate of potash by treating a solution of bichromate
of soda with sulphate of potash and crystallising out or similarly separating the
bichromate of potash thereby formed, substantially as herein set forth.
(6.) The manufacture of bichromate of ammonia by treating a solution of
bichromate of soda with sulphate of ammonia and crystallising out or similarly
separating the bichromate of ammonia thereby formed, substantially as herein set
forth.