IMPROVEMENTS IN THE MANUFACTURE OF BICHROMATE OF SODA
Year: 1884

page_text: [Reprint. This Specification has been reprinted in consequence of an amendment
made by Order of the Comptroller prior to the sealing of the Patent.]
PROVISIONAL SPECIFICATION.
I, WILLIAM JAMES CHRYSTAL, of Glasgow, in the County of Lanark, Chemist,
do hereby declare the nature of my said Invention for "IMPROVEMENTS IN THE
MANUFACTURE OF BICHROMATE OF SODA"; to be as follows:-
My Invention relates to improvements in the manufacture of bichromate of soda.
In carrying out the Invention, I take a mixture of chrome ore, or other substance
yielding chrome, with lime, and hydrate, carbonate, nitrate, or sulphate of soda, or
any mixture or combination of these salts, in such proportions as may be found
expedient, and calcine or furnace the mixture in the usual way until decomposition
is effected. I then lixiviate the furnaced mass in tanks or vessels, and treat it
with salts of soda, such as the carbonate or sulphate; or in lieu of, or in addition
to, the use of such salts, I add sulphuric acid, carbonic acid or other acid, to effect
the decomposition of such insoluble chromates as may be present in the mass.
Either before or after evaporation, I subject the neutral or partly acid liquor
resulting from this process of treatment, to the action of an acid such as sulphuric,
nitric, muriatic, acetic, or carbonic, in order to convert the neutral chromate of soda
into the bichromate of soda, and into the sulphate, nitrate, muriate, acetate,
carbonate, or other salt of soda, corresponding to the acid employed. The solution
of these salts is then concentrated to such a degree as to partially or totally
eliminate the sulphate or other corresponding soda salt, leaving the bichromate of
soda in solution. The solution of bichromate of soda may then, if desired, be
evaporated to dryness, and calcined and fused or finished in any other way. By
concentrating the solution to a sufficient degree I altogether eliminate the soda
salts and leave in solution perfectly pure bichromate of soda. This latter part of
the process I also employ to eliminate the soda salts from solutions of impure
bichromate of soda produced by any other known method, and I obtain therefrom
a solution of pure bichromate of soda. The solution so produced is then placed in
suitable vessels and crystallised. The crystals then contain about. 14 per centum
of water of combination, and are represented by the formula 2 Na₁ Cг₂ O7 + 5 H₂ O.
The solution may however, before crystallisation, be concentrated beyond the point
at which the soda salts are eliminated as above mentioned, in which case the
crystals may contain any smaller quantity of water than corresponds to the formula
given.
m
1004

page_text: :
COMPLETE SPECIFICATION.
I, WILLIAM JAMES CHRYSTAL of Glasgow, in the county of Lanark, Chemist,
do hereby declare the nature of my said invention for "IMPROVEMENTS IN THE
MANUFACTURE OF BICHROMATE OF SODA," and in what manner the same is to be
performed, to be particularly described and ascertained in and by the following
statement:-
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>
My Invention relates to improvements in. the manufacture of bichromate of soda.
In carrying out the invention, I take a mixture of chrome ore, or other substance.
yielding chrome, with lime and hydrate, carbonate, nitrate, or sulphate of soda,
or any mixture or combination of these salts in such proportions as may be
found expedient, and calcine or furnace the mixture in the usual way until decom-
position is effected. I then lixiviate the furnaced mass in tanks or vessels, and treat
it with salts of soda, such as the carbonate or sulphate; or in lieu of, or in
addition to, the use of such salts, I add sulphuric acid, carbonic acid, or other
acid, to effect the decomposition of such insoluble chromates as may be present in
the mass.
Either before, after, or during evaporation, I subject the neutral or partly acid
liquor resulting from this process of treatment, to the action of an acid, such as
sulphuric, nitric, muriatic, acetic, or carbonic, in order to convert the neutral
chromate of soda into the bichromate of soda, and into the sulphate, nitrate,
muriate, acetate, carbonate, or other salt of soda, corresponding to the acid
employed. The solution of these salts is then concentrated to such a degree as to
partially or totally eliminate the sulphate or other corresponding soda salt, leaving
the bichromate of soda in solution. The solution of bichromate of soda may then,
if desired, be evaporated to dryness, and calcined and fused or finished in any other
way. By concentrating the solution to a sufficient degree I altogether eliminate
the soda salts and leave in solution perfectly pure bichromate of soda. This latter
part of the process is also employed to eliminate the soda salts from solutions of
impure bichromate of soda produced by any other well-known method, and I
obtain therefrom a solution of pure bichromate of soda. The solution so produced
is then placed in suitable vessels and crystallised. The crystals then contain about
14, per centum of water of combination, and are represented by the formula
2 Na Cr₂ O + 5 H₂ O. The solution may however, before crystallisation, be
concentrated beyond the point at which the soda salts are eliminated as above
mentioned, in which case the crystals may contain any smaller quantity of water
than corresponds to the formula given.
Bichromate of soda has been hitherto produced in a dried or fused state, but
always more or less impure. By the mode described, bichromate of soda is
produced in a state of absolute purity.
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,-
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First. The whole process of manufacturing bichromate of soda which consists in (1)
furnacing a mixture of chrome ore with lime and a suitable soda salt in the usual

page_text: way, (2) then lixiviating the furnaced mass and treating it with salts of soda with or
without the addition of an acid, (3) then subjecting the solution resulting from
lixiviation to the action of an acid for the purpose of converting the neutral
chromate into the bichromate of soda, (4) then concentrating the solution to such a
degree (that is, from about 150 to 180 degrees Twaddell) as to eliminate the soda
salts and leave in solution perfectly pure bichromate of soda, substantially as
described.
Second. The manufacture of pure bichromate of soda substantially as herein
described.