Year: 1886

page_text: Date of Application, 1st July, 1886.
Complete Left, 11th Mar., 1887.
Complete Accepted. 15th Apr., 1887.
I, JAMES PARK, of the Millburn Chemical Works, Glasgow, in the County of
Lanark, North Britain, Chemist, do hereby declare the nature of this Invention to be
as follows, that is to say :-
"
My said Invention has for its object the manufacture of bichromate of ammonia in
an improved and economical manner; and it consists essentially in obtaining the
bichromate of ammonia from bichromate of calcium by double decomposition with
sulphate of ammonia.
In carrying out my Invention I employ chromate of calcium as obtained by any
known process. For example the chromate of calcium may be what is obtained in
the ordinary process of making bichromate of soda, and of which a larger quantity
can be produced at pleasure by diminishing the proportion of alkali or soda salt.
Or the chromate of calcium may be obtained by adding a soluble salt of calcium such
as the chloride to a solution of chromate of soda.
The chromate of calcium, in a state of greater or less purity is converted into
bichromate of calcium by adding the requisite quantity of sulphuric acid, and the
bichromate of calcium is converted into bichromate of ammonia by the addition of a
strong solution of sulphate of ammonia.
The bichromate of ammonia thus produced is in solution and is separated by
decantation or filtration from the precipitated sulphate of lime and the solution and
washings are evaporated to about 50 degrees, Twaddell; and when the concentrated
solution cools the bichromate of ammonia separates out in crystals.
Dated this thirtieth day of June 1886

page_text: Improvements in the Manufacture of Bichromate of Ammonia.
I, JAMES PARK, of the Millburn Chemical Works, Glasgow, in the County of
Lanark, North Britain, Chemist, do hereby declare the nature of this invention and
in what manner the same is to be performed, to be particularly described and ascer-
tained in and by the following statement, that is to say :—
My said Invention has for its object the manufacture of bichromate of ammonia in
an improved and economical manner; and it consists essentially in obtaining the
bichromate of ammonia from bichromate of calcium by double decomposition with
sulphate of ammonia.
In carrying out my Invention I employ chromate of calcium as obtained by any
known process. For example the chromate of calcium may be what is obtained in
the ordinary process of making bichromate of soda, and of which a larger quantity
can be produced at pleasure by diminishing the proportion of alkali or soda salt. Or
the chromate of calcium may be obtained by adding a soluble salt of calcium such as
the chloride to a solution of chromate of soda.
The chromate of calcium, in a state of greater or less purity is converted into,
bichromate of calcium by adding the requisite quantity of sulphuric acid,. and for
this purpose I put the chromate of calcium, together with as much water as will make
a thin cream, into a circular pan provided with a suitable agitating apparatus, such as
a rotating vertical shaft with horizontal arms fitted with trailing rakes. The chromato
of calcium being kept in suspension in the water by the agitation of the rakes, has
added to it sulphuric acid in sufficient quantity to convert it into bichromate of
calcium. When this has been accomplished sulphate of ammonia is added either in
the solid state or in solution in water or dissolved in the mother liquor left at a later
stage of a previous operation. The sulphate of ammonia whether in the solid state
or in solution is added in sufficient quantity to form a complete double decomposition
with the bichromate of calcium. The mixture is afterwards run off into tanks and
the insoluble sulphate of calcium formed is separated by filtration. After the solution
of bichromate of ammonia has been drawn off the sulphate of calcium is washed with
hot water until free from the ammonia salt. The filtrate and washings are then
evaporated to about 50 degrees Twaddell, and run into crystallising tanks.
The boiling of the solution should be done in a pan heated by means of a closed
steam coil or jacket and not in an open-fired pan unless care is taken not to overheat
the part of the pan above the surface of the liquid.

page_text: The mother liquor from the crystallised bichromate of ammonia can either be
returned to the evaporating pan or used for dissolving fresh quantities of sulphate of
ammonia for subsequent operations.
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 :-
The manufacturing of bichromate of ammonia from bichromate of calcium by
double decomposition with sulphate of ammonia substantially in the manner herein-
before described.