Process for Manufacturing Metallic Sulphides Electrolytically.
Year: 1898

page_text: Date of Application, 26th Apr., 1898-Accepted, 11th June, 1898
COMPLETE SPECIFICATION.
Process for Manufacturing Metallic Sulphides Electrolytically.
We, JOSEPH WILLIAM RICHARDS, a subject of the Queen of Great Britain, resid-
ing at Bethlehem, in the State of Pennsylvania, United States of America,
Electrical Chemist, and CHARLES WILLIAM ROEPPER, a citizen of the United
States, residing at Bethlehem, aforesaid, Electrical Chemist, do hereby declare
the nature of this invention and in what manner the same is to be performed to
be particularly described and ascertained in and by the following statement:-
Our invention relates to the manufacture of metallic sulphides, and has for its
object to cheapen the production of these compounds as commercial articles, and
also to obtain them, in the case of those sulphides which are useful as pigments,
in the condition in which they are most desired for this purpose.
The process by which we accomplish this is one of extreme simplicity and
directness, and also one in which the physical conditions attending the production
of the sulphides (such as temperature, velocity of production and concentration of
the solution) are easily controlled, with a corresponding resultant economy of
material and superior quality of product.
The general principle of our invention consists in employing the metal whose
sulphide it is desired to obtain as an anode in the electrolysis of a solution con-
taining a hyposulphite salt, the sulphide sought for being thus formed from the
anode and precipitated. In case a complex sulphide is desired, the anode is
formed of an alloy of those metals whose mixed sulphides are to be obtained.
In describing the process specifically we will choose as an instance the produc-
tion of cadmium sulphide which, as is well known constitutes commercially the
pigment known as cadmium yellow. The anode is made of metallic cadmium,
and may be cast in such shape, whether flat, square or round, as may be desired.
A carbon electrode may be used as cathode, or any other suitable substance not
attacked by the electrolyte or the products set free upon it. Metallic cadmium
itself fills these requirements and may be used as a cathode. As electrolyte we
employ a solution of sodium hyposulphite, (also known as thiosulphate). A ten
per cent. solution will be found suitable, but the strength of solution may vary
greatly according to the conditions of manufacture. Instead of sodium hypo-
sulphite, other soluble hyposulphites may be employed with the same results.
As the electrolysis proceeds the hyposulphite is decomposed, hydrogen being
set free at the cathode, while the nascent sulphur combines with the metal of the
anode forming a sulphide, which, as it is insoluble in the solution, deposits in the
vessel.
The shape and arrangement of the electrolysing apparatus is immaterial and
may be adjusted to suit the convenience of the operator. The precipitated
sulphide should from time to time be removed from the bottom of the tank, when
it may be successively filtered, washed, dried and pulverized. The solution which
is filtered out may, if it still contains hyposulphite, be poured again into the
electrolytic tank.
In the case of some sulphides, and among them is cadmium sulphide, we have
found that the precipitate is of the best color when it is formed from a hot electro-
yte, say, at 75° C. In the case of other sulphides, as in the case of antimony

page_text: sulphide, a better color is obtained from a cold solution than from a hot one. The
presence of other soluble salts in addition to the hyposulphites frequently pro-
motes the formation of the precipitated sulphide and improves its physical con-
dition. Thus in the case of cadmium sulphides, we have found that the addition
of five per cent. of sodium chloride to the electrolyte increases its conductivity,
rendering the process more rapid and efficient, while at the same time it produces
a precipitate of a brighter shade of yellow.
Our process is applicable to the production of all metallic sulphides except those
which are soluble in the solution which is used in the electrolyte.
We are aware that it is common practice to make metallic sulphides by purely
chemical means, such as dissolving the metals in acid, passing hydrogen sulphide
through the solution and collecting the precipitated metallic sulphide.
We are also aware that it has been proposed to use a metal as an anode in a
solution containing an acid constituent capable of forming a soluble salt with the
metal, thus bringing the metal into solution, and to then simultaneously pass into
the solution hydrogen sulphide, the metallic sulphide being precipitated. It is
evident that this method differs from the purely chemical method only in that the
solution of the metallic salt is obtained electrolytically, instead of chemically.
These processes are further objectionable in that they necessitate the employ-
ment of hydrogen sulphide. The process invented by us differs from these in
that the sulphur necessary to form the insoluble metallic sulphide is furnished
by the direct electrolysis of a hyposulphite solution.
Having now particularly described and ascertained the nature of our said
invention, and in what manner the same is to be performed we declare that what
we claim is :-
The process of manufacturing metallic sulphides, which consists in employing
an anode of or containing the metal or metals whose sulphide is desired in a solu-
tion containing a hyposulphite salt as an electrolyte in conjunction with any
suitable cathode passing a current of electricity therethrough and precipitating
the sulphide of the metallic base present in the anode, substantially as described.
Dated this 25th day of March 1898.
CARPMAEL & Co.,
Agents for the Applicants.