IMPROVEMENTS IN THE PRODUCTION OF PIG- MENTS
Year: 1877

page_text: LETTERS PATENT to Stephen Williams, of Chelsea, in the County of Middlesex,
Chemist, for the Invention of "IMPROVEMENTS IN THE PRODUCTION OF PIG-
MENTS."
Sealed the 15th May 1877, and dated the 24th January 1877.
PROVISIONAL SPECIFICATION left by the said Stephen Williams at the Office
of the Commissioners of Patents on the 24th January 1877.
STEPHEN WILLIAMS, of Chelsea, in the County of Middlesex, Chemist.
"IM-
PROVEMENTS IN THE PRODUCTION OF PIGMENTS."
.
This Invention relates to the production of pigments, and consists in the improved
production of sulphide of zinc and of sulphate of baryta.
In carrying out my Invention I proceed as follows:-To a solution of crude
chloride of zinc I add sufficient polysulphide of calcium, so as to precipitate the
whole of the zinc contained in the solution as a sulphide, leaving chloride of calcium
in the supernatant solution, together with salts of soda previously existing in the
crude and impure chloride of zinc. I then add chloride of barium, by preference in
solution and in an equivalent proportion to the zinc previously employed. To this
mixed solution I then add, by preference in solution, sulphate of sodium so as to
precipitate the baryta as sulphate. It will be found by adopting this process that
no calcium sulphate will be precipitated in combination with the barium sulphate.
To these precipitates I find it advantageous to add magnesia or carbonate of
magnesia, preferably obtained by precipitation from a salt of magnesia in the
ordinary way, and intimately mix the whole. The precipitates thus obtained are
collected, filtered, washed, and submitted to calcination in order that the desired
pigments may be obtained. By the employment of this process I avoid employing
sodium sulphide as also of free sulphuric acid, and I obtain the finished pigments
free from sulphate of lime which is most advantageous.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by the
said Stephen Williams in the Great Seal Patent Office on the 24th July
1877.
STEPHEN WILLIAMS, of Chelsea, in the County of Middlesex, Chemist.
PROVEMENTS IN THE PRODUCTION OF PIGMENTS."
"IM-
My said Invention relates to the improved production of pigments and of sulphide
of zinc and of sulphate of baryta to be employed for such purpose.
To a
In carrying out my said Invention I proceed in the following manner :-
solution of crude chloride of zinc I add sufficient polysulphide of calcium to effect
the precipitation of the whole of the zinc contained in the solution as a sulphide,
leaving chloride of calcium in the supernatant solution together with any impurities
previously existing in the crude and impure chloride of zinc. I then add chloride
of barium, by preference in solution and in an equivalent proportion to the zinc
previously employed. To this mixed solution I then add, by preference in solution,
sulphate of sodium so as to precipitate the baryta as sulphate. It will be found by
adopting this process that no calcium sulphate will be precipitated in combination
with the barium sulphate. To these precipitates I find it advantageous to add
magnesia or carbonate of magnesia, preferably obtained by precipitation from a
salt of magnesia in the ordinary way, and intimately mix and incorporate the same
with the before-mentioned precipitates. The mixed precipitates thus obtained are
collected, filtered, washed, and submitted to calcination in order that the desired
pigments may be obtained. If desired, the magnesia may be added to the com-
pounds of zinc and of baryta, subsequently to and in lieu of, previously to their
calcination. By the use of this process I avoid employing sodium sulphide, as also
free sulphuric acid, and I obtain the finished pigments free from sulphate of lime,
which result I have found most advantageous in practice.
I find that magnesia added either to the mixed precipitates before calcination or
subsequent thereto in the proportion of about one part of magnesia to about one
hundred parts by weight will give good results, but I do not limit myself to such
proportions.
Having now described and particularly ascertained the nature of the said Inven-
tion and the manner in which the same is or may be used or carried into effect, I
would observe in conclusion that what I consider to be novel and original and
therefore claim as the Invention secured to me by the herein-before in part recited
Letters Patent, is,-
First. The production of pigments, substantially in the manner herein-before
described.
Second. The employment of magnesia in conjunction with sulphide of zinc, either
before or after calcination, together with sulphate of baryta for the purposes. herein-
before described.
In witness whereof, I, the said Stephen Williams, have to this my Specifi-
cation set my hand and seal, this Twenty-third day of July, One thousand
eight hundred and seventy-seven.
STEPHEN WILLIAMS. (L.S.)