IMPROVEMENTS IN THE MANUFACTURE OF CHROMATES AND BICHROMATES
Year: 1884

page_text: I, WILLIAM JOHN ALEXANDER DONALD of Number Two Belgrave Terrace Hill-
head Glasgow, Secretary and Commercial Manager of The Eglinton Chemical
Company Limited, Glasgow 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 to produce chromates and bichromates of soda
by new methods and more economically than they have hitherto been manu-
factured.
In the first stages of the manufacture of these substances as I practice it I employ
the process at present in use to manufacture chromates of potash; but I substitute
for the potash salts sulphate, carbonate or caustic soda. On lixiviating the batches
obtained from the chrome furnaces, chromate of soda is obtained in solution along
with certain quantities of sulphate of soda &c. In order to eliminate the sulphate
of soda from this solution, which it is difficult and almost impossible to do, entirely
by evaporation or crystallisation, I add to the solution chloride of calcium or
chloride of barium (or other soluble chloride having a reaction on sulphate of soda
to produce a more or less insoluble sulphate) in the quantity required to combine
with the contained sulphate of soda. The effect of the action which takes place is
to leave the chromate of soda in solution and to form sulphate of lime or sulphate
of barium or other sulphate (according as chloride of calcium or chloride of barium
or other chloride is respectively used) and chloride of sodium, which are then
readily separated by known means owing to their lesser solubility. These sub-
stances being precipitated and crystallised chromate of soda in a very pure state is
obtained by further evaporation and crystallisation.
I convert the chromate of soda so obtained into bichromate of soda, by adding to
the solution thereof sulphuric acid or hydrochloric acid in such quantity as to com-
bine with one half of the soda of the chromate of soda, which is thereby converted
into sulphate of soda or chloride of sodium. The sulphate of soda, I afterwards
eliminate in the manner hereinbefore stated in describing the manufacture of
chromate of soda, producing chloride of sodium and sulphate of calcium if chloride
of calcium be used, or chloride of sodium and sulphate of barium, if chloride of
barium be used, which on the liquors being evaporated down are precipitated,

page_text: leaving pure or almost pure bichromate of soda in solution to be obtained as a salt
by evaporation or in the crystalline form, by evaporation and crystallization. If
hydrochloric acid shall have been used instead of sulphuric acid, I eliminate the
same by evaporating the liquor in the same way as when I use sulphuric acid.
In making bichromate of soda as before described, the sulphate of soda etc. may
not be eliminated from the chromate of soda, from which the bichromate of soda is
to be made, as they, with the additional sulphates made in converting the chromate
into bichromate, may be eliminated together, after the formation of the bichromate
of soda.
If chloride of barium be used in preference to chloride of calcium the sulphate of
barium obtained as a by-product is available for sale as such or can be converted
again into chloride of barium by known means.
The chloride of calcium, which I use is preferably that which is obtained as a
waste by-product in the manufacture of bleaching powder but I also obtain it by
treating carbonate or caustic lime with hydro-chloric acid.
Dated this 19th den of Mah 1001

page_text: I WILLIAM JOHN ALEXANDER DONALD of 2 Belgrave Terrace, Hillhead,
Glasgow, Secretary and Commercial Manager of the Eglington Chemical Company
Limited, Glasgow in the County of Lanark Scotland do hereby declare the nature
of my invention for "IMPROVEMENTS IN THE MANUFACTURE OF CHROMATES AND
BICHROMATES and in what manner the same is to be performed to be particularly
described and ascertained in and by the following statement:-
31
My invention has for its object to produce chromates and bichromates of soda
by new methods and more economically than they have hitherto been manu-
factured.
In the first stages of the manufacture of these substances as I practice it I employ
the process at present in use to manufacture chromates of potash but I substitute
for the potash salts sulphate carbonate or caustic soda. On lixiviating the batches
obtained from the chrome furnaces, chromate of soda is obtained in solution along
with certain quantities of sulphate of soda &°. In order to eliminate the sulphate
of soda from this solution which it is difficult and almost impossible to do by
evaporation or crystallization I add to the solution chloride of calcium or chloride
of barium (or other soluble chloride having a reaction on sulphate of soda to
produce a more or less insoluble sulphate) in the quantity required to combine with
the contained sulphate of soda. The effect of the action which takes place is to
leave the chromate of soda in solution and to form sulphate of lime or sulphate of
barium or other sulphate (according as chloride of calcium or chloride of barium or
other chloride is respectively used) and chloride of sodium which are then readily
separated by known means owing to their lesser solubility. These substances
being precipitated and crystallized chromate of soda in a very pure state is obtained
by further evaporation and crystallization.
I convert the chromate of soda so obtained into bichromate of soda by adding to
the solution thereof sulphuric acid or hydrochloric acid in such quantity as to
combine with one half of the soda of the chromate of soda which is thereby
converted into sulphate of soda or chloride of sodium. The sulphate of soda I
afterwards eliminate in the manner hereinbefore stated in describing the manu-
facture of chromate of soda producing chloride of sodium and sulphate of calcium
if chloride of calcium be used or chloride of sodium and sulphate of barium if
chloride of barium be used which on the liquors being evaporated down are
precipitated leaving pure or almost pure bichromate of soda in solution to be
obtained as a salt by evaporation or in the crystalline form by evaporation and
crystallization. If hydrochloric acid shall have been used instead of sulphuric acid
I eliminate the same by evaporating the liquor in the same way as when I use
sulphuric acid.
In making bichromate of soda as before described the sulphate of soda etc. may
not be eliminated from the chromate of soda from which the bichromate of soda is
to be made as they with the additional sulphates made in converting the chromate
into bichromate may be eliminated together after the formation of the bichromate
of soda.
If chloride of barium be used in preference to chloride of calcium the sulphate of
barium obtained as a by-product is available for sale as such or can be converted
again into chloride of barium by known means.
The chloride of calcium which I use is preferably that which is obtained as a
waste by-product in the manufacture of bleaching powder but I also obtain it by
treating carbonate or caustic lime with hydrochloric acid,

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 means herein described for the treatment of the crude solution to effect
the separation of sulphate of soda from chromate of soda; such treatment consisting
in the addition of chloride of calcium, chloride of barium or other soluble chloride
having a reaction on the sulphate of soda to produce chloride of sodium and a more
or less insoluble sulphate both of which on the solution being concentrated are
deposited and easily removed.
(2). In the process of obtaining bichromate of soda from chromate of soda, the
separation by like means of the product from sulphate of soda which is the bye-
product substantially as described.
(3). The process of making bichromate of soda consisting in treating mixed
chromate and sulphate of soda as obtained from the crude solution first with acid
to convert the chromate into bichromate and then with a soluble chloride having a
reaction on the sulphate of soda to produce chloride of sodium and a more or less
insoluble sulphate substantially as described.
(4). The processes for the manufacture of chromate and bichromate of soda
substantially as described.