IMPROVEMENT IN THE MANUFACTURE OF BICHROMATE OF POTASH
Year: 1885

page_text: I, PETER RÖMER, manufacturer, residing in Elberfeld, Prussia, do hereby declare
the nature of my said invention for an "IMPROVEMENT IN THE MANUFACTURE OF
BICHROMATE OF POTASH," and in what manner the same is to be performed, to be
particularly described in and by the following statement :-
Hitherto bichromate of potash is directly manufactured from chrome-iron ore
by mixing the said ore with lime and potash, and roasting the mixture in an
oxydizing flame. The chromic oxide is thereby oxydized to chromic acid which
combines with the potash to potassium-bichromate. The latter is then separated
from the mass by lixivation with water.
This method is, however, disadvantageous on account of the high temperature
required being a source of great losses of potassium. A part of the same is
volatilized during the process, while another part combines with the silicon present
in the lime and the chrome-iron ore.
In order to avoid these inconveniencies, I proceed after the following new
method, which consists in decomposing bichromate of sodium by means of chloride
of potassium in the wet way.
Sodium-bichromate, such as prepared in the usual manner, is dissolved in boiling
water to a concentrated solution. To the boiling, liquor, chloride of potassium is
added, preferably also in aqueous solution. The whole is then for some time
maintained at the boiling point. By this treatment the soda and potash compounds
are caused to interchange the chromic acid and the chlorine, and when the liquor
is allowed to cool, bichromate of potassium falls to the bottom in large quantities.
The process may be expressed by the following chemical formula:
Nº Cг, 0, + 2 K Cl = K₂ Cг, O, + 2 Na CL
The potassium-bichromate separated out, is removed from the mother-lye in
any suitable manner; then it is washed with cold water and finally brought
into commercial form by redissolving and allowing it to stand and crystallize.
The mother-lye consists in a solution of chloride of sodium together with a
certain amount of bichromate of potassium, is concentrated by evaporation so that
the chloride of sodium separates out therefrom; the latter is then removed and
washed with hot water which is added to the first lye. From this the rest of the
bichromate of potassium is obtained by evaporation.

page_text: If the solutions of sodium-bichromate and of chloride of potassium applied in
the process, possess the proper degree of concentration, up to 80 per cent of the
theoretical amount of the potassium-bichromate to be obtained, may be separated
at once; the remaining 20 per cent are found in the mother-lye and removed
therefrom as described.
The following proportions have given good results:
2 Na, Cr O, + 2 H CI + 2 K Cl = K₂ Cr₂ 0, + 4 Na CI + H₂ 0.
Having now particularly described and ascertained the nature of my said 1
invention and in what manner the same is to be performed, 1 declare that what
I claim is
The method of manufacturing bichromate of potash which consists in adding
a solution of chloride of potassium to a boiling concentrated solution of sodium-
bichromate, or a like solution of sodium mono-chromate to which hydrochloric acid
or another suitable acid has been added, in continuing to boil the liquor for some
time, in allowing the same to cool, and in separating the bichromate of the mother-
lye, substantially as set forth.