IMPROVEMENTS IN THE MANU- FACTURE OF CHROMATES OF POTASH AND SODA
Year: 1877

page_text: LETTERS PATENT to Charles Stuart Gorman, of Irvine, in the County of Ayr,
North Britain, Chemist, for the Invention of "IMPROVEMENTS IN THE MANU-
FACTURE OF CHROMATES OF POTASH AND SODA."
Sealed the 15th September 1877, and dated the 21st July 1877.
PROVISIONAL SPECIFICATION left by the said Charles Stuart Gormau at
the Office of the Commissioners of Patents on the 21st July 1877.
CHARLES STUART GORMAN, of Irvine, in the County of Ayr, Chemist.
PROVEMENTS IN THE MANUFACTURE OF CHROMATES OF POTASH AND SODA."
"IM-
Under the ordinary process of manufacturing chromates of potash and soda very
considerable quantities of the alkaline salts are lost by volatilization at the high
temperatures used, and much of the sesqui-oxide of chromium is left in the waste
or residual products, and the object of the present Invention is to more effectually
utilize the sesqui-oxide of chromium, and prevent the waste of alkaline salts.
Under one modification the chrome ore, lime, and carbonate of potash in the usual
proportions are calcined or roasted in a furnace in the ordinary manner, but when
the calcination is nearly completed, or the charge been seven hours in the furnace,
it is then withdrawn and a further quantity of, say, from 10 to 14 per cent. of
carbonate of potash or soda, or caustic potash or soda, or a mixture of both, either
in the solid or liquid state, is added to the charge, which is then heated at a low
temperature of 1000° Fahrenheit (either in the same or a separate furnace) to
convert the sesqui-oxide of chromium into chromates, and thereby save the great
loss of that material which takes place under the ordinary process.
Under a second modification the chrome ore, caustic lime, or carbonate of lime
are brought to a white heat in a reverberatory or "Siemens"" furnace until the
ore is decomposed, the iron in the ore peroxidised, and the sesqui-oxide of chromium
set free. The charge or "batch" is then drawn from the furnace and mixed with a
proportion of about sixty per cent. of caustic potash or carbonate of potash, and
charged into a revolving furnace, preferably that known as "Jones' furnace," in
which it is treated at a temperature of about 1000 degrees Fahrenheit, to prevent
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page_text: the great loss of alkaline salts by volatilization which takes place under the much
higher temperatures heretofore used in the ordinary process.
Thus by this Invention a greater yield of chromates is obtained with much less
loss of sesqui-oxide of chromium or of alkali than by the ordinary process of manu-
facturing chromates.
SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Charles Stuart Gorman in the Great Seal Patent Office on the
21st January 1878.
CHARLES STUART GORMAN, of Irvine, in the County of Ayr, North Britain, Chemist.
"IMPROVEMENTS IN THE MANUFACTURE OF CHROMATES OF POTASH AND SODA."
Under the ordinary process of manufacturing chromates of potash and soda as
hitherto conducted, very considerable quantities of the alkaline salts are lost by
volatilization at the high temperatures used, and much of the sesqui-oxide of
chromium employed in the process is left in the waste or residual products, and the
object of the present Invention is to utilize more effectually than has hitherto been
done the sesqui-oxide of chromium, and to prevent undue waste of alkaline salts.
My present Invention relates to two processes, one being a much improved
modification based in part on the old process, and the other being a new and very
useful process, which will be found in practice to be far more beneficial than the
process hitherto employed.
According to my first process above referred to the chrome ore, lime, and car-
bonate of potash in the usual proportions are well mixed, and are calcined or
roasted in a furnace at a red heat in the ordinary manner, but when the calcination
is nearly completed, as will be found to be the case ordinarily when the charge has
been in the furnace for about seven hours, it is then withdrawn and allowed to
cool; and according to one part of my present Invention I add to the charge (either
before or after being withdrawn to cool) a further quantity, say, from 10 to 20 per
cent., of carbonate of potash, or of its chemical equivalent of carbonate of soda,
caustic potash or soda, or a mixture of both, either in the solid or liquid state. The
charge is then refurnaced at a much lower temperature than that represented by
the red heat above mentioned, or, say, at from 800° to 1200° Fahrenheit, according
to the quality of the ore (either in the same or a separate furnace), the result being
to convert the sesqui-oxide of chromium into chromates by combining with the
alkaline salts, and thereby save the great loss of that material which takes place
under the ordinary process.
I will next proceed to describe another process which forms another part of my
Invention. I employ chrome ore, caustic lime, or carbonate of lime, and the pro-
portions which I find most beneficial are as follows, that is to say:-300 parts of
chrome ore and 200 parts of caustic lime, or 358 parts of carbonate of lime, or its
equivalent of carbonate of magnesia or carbonate of barytes. These are mixed, and
are treated at a much higher heat than is used in the other process above described,
Bay, to the heat corresponding to the white heat obtained in a reverberatory or a
"Siemens"" furnace, or in any ordinary chrome furnace, the heat being continued

page_text: until the ore is decomposed, the iron in the ore peroxidised, and the sesqui-oxide of
chromium set free. The charge or "batch," which may be taken to consist of about
5 to 6 hundredweights, is then drawn from the furnace to cool, and mixed with a
proportion of about 240 pounds of carbonate of potash, or its chemical equivalent
of sulphate of potash or carbonate of soda, or its equivalent caustic potash or soda,
either in the solid or liquid state; but if in the liquid state, from 50 to 100 pounds
of burned lime is added to dry the batch, which is then charged into the ordinary
chrome furnace or a revolving furnace, in which it is treated at a comparatively low
temperature, say, from 800° to 1200° Fahrenheit, according to the quality of the
ore, the result being to effect the requisite combination, and convert the sesqui-oxide
of chromium into chromates of potash or soda, and so prevent the great loss of
alkaline salts by volatilization which takes place when the entire process is carried
on throughout at the temperatures heretofore used in the ordinary process.
Thus by my Invention a greater yield of chromates is obtained with much less
loss of sesqui-oxide of chromium or of alkaline salts than is found to result from the
ordinary process of inanipulating chromates.
Having now described the nature of my said Invention and the manner of per-
forming the same, I have to state that I do not confine myself to the precise pro-
portions of the substances herein specified, but what I consider novel and original
and therefore claim as the Invention secured to me by the herein-before in part
recited Letters Patent are,-
First. The manufacture of chromate of potash or chromate of soda by the process
conducted substantially as herein firstly described, wherein a secondary process of
furnacing at a comparatively low temperature is employed after or in combination
with the process of furnacing conducted at about a red heat, as ordinarily used.
Second. The manufacture of chromate of potash or chromate of soda by the
process conducted substantially as herein secondly described, wherein a furnacing at
a very high temperature is followed by a secondary furnacing at a comparatively
low temperature.
Third. The use in the manufacture of chromates, carried on substantially in the
manner above mentioned, of the secondary process of furnacing at a low temperature,
employed as and for the purpose substantially as herein described.
In witness whereof, I, the said Charles Stuart Gorman, have hereunto set
my hand and seal, this Sixteenth day of January, in the year of our Lord
One thousand eight hundred and seventy-eight.
CHARLES STUART GORMAN. (L.S.)