Year: 1887

page_text: Date of Application, 25th Mar., 1887
Complete Left, 24th Dec., 1887
Complete Accepted, 10th Feb., 1888
I, SILVANUS PHILLIPS THOMPSON of 20 Arundel Gardens, North Kensington, in
the county of Middlesex, Doctor of Science, do hereby declare the nature of this
invention to be as follows:-
My invention relates to improvements in the deposition by electric currents of
the metal cobalt and has for its object the deposition of the said metal in films of
greater tenacity, density, and brilliance of tint, than have heretofore been obtainable
with certainty.
The solution for depositing cobalt may consist of sulphate or chloride of cobalt
or of the double sulphate of chloride or cobalt and ammonium, to which has also
been added sulphate or chloride of magnesium, or other suitable soluble salt of
magnesium, or a mixed soluble salt of magnesium and ammonium may be added to
the solution of cobalt salts. The citrate of magnesium is a useful salt, and it may be
formed in the solution by adding citric acid and magnesia or carbonate of magnesium
to the solution, citrate of ammonium or simply citric acid may be added to the
solution. As an example of one way of carrying out the invention a solution may be
made by adding to ten pounds of water, one pound of the double sulphate of cobalt
and ammonium, half a pound of sulphate of magnesium, half a pound of sulphate of
ammonium, one ounce of citric acid and two ounces of carbonate of ammonium. The
solution may be used warm or cold, but if heated to at least 35 degrees of the centi-
grade thermometer gives a brilliant deposit with greater readiness than if used cold.
Anodes of cobalt are preferred, but insoluble anodes of carbon may be employed. In
the latter case the solution becomes sooner impoverished of metal and requires
replenishing by the addition of cobalt salt. It must be understood that I do not bind
myself to the above exact proportions: for I find by experiment that if the above
solution is diluted by the addition of an equal quantity of water to half its strength it
will yield a good deposit of metal, but in that case a stronger current in proportion
to the surface of deposition, should be turned on from the dynamo or battery.
The best current-density I find to be not less than one ampere nor more than

page_text: four amperes per square foot of depositing surface, but a somewhat stronger current
may be advantageously employed during the first few minutes of deposition so as to
secure a rapid striking of the film on the surface, the current-density being
diminished so soon as the surface is once covered with a film.
The pieces to receive the deposit should be scrupulously cleansed and prepared in
the same well known manners as are usual for deposits of nickel, and they may be
polished after deposition in any of the ways known for polishing nickel-plated
goods.

page_text: Improvements in Electro-deposition of Cobalt.
I, SILVANUS PHILLIPS THOMPSON of 20 Arundel Gardens, North Kensington, in
the County of Middlesex, Doctor of Science, 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:-
My invention relates to improvements in the deposition by electric currents of the
motal cobalt and has for its object the deposition of the said metal in films of greater
tenacity, density, and brilliance of tint, than have heretofore been obtainable with
certainty.
The solution for depositing cobalt may consist of sulphate or chloride of cobalt or
of the double sulphate of chloride of cobalt and ammonium, to which has also been
added sulphate or chloride of magnesium, or other suitable soluble salt of magnesium,
or a mixed soluble salt of magnesium and ammonium may be added to the solution
of cobalt salts. The citrate of magnesium is a useful salt, and it may be formed in
the solution by adding citric acid and magnesia or carbonate of magnesium to the
solution citrate of ammonium or simply citric acid may be added to the solution. As
an example of one way of carrying out the invention a solution may be made by
adding to ten pounds of pure water, one pound of the double sulphate of cobalt and
ammonium, half a pound of sulphate of magnesium, half a pound of sulphate of
ammonium, one ounce of citric acid and two ounces of carbonate of ammonium. The
solution may be used warm or cold, but if heated to at least 35 degrees of the centi-
grade thermometer gives a brilliant deposit with greater readiness than if used cold.
As another example of the carrying out of this invention I may prepare the solution
as follows.
Half a pound of sulphate of cobalt dissolved in four pounds of pure water: quarter
pound of sulphate of magnesium dissolved in four pounds of pure water: these
solutions mixed and pure water added to make up to one gallon. A quantity of
sulphate of ammonium not exceeding half a pound may with advantage be added.
By pure water is meant simply newly boiled and filtered or preferably distilled.
Anodes of cobalt are preferred, but insoluble anodes of carbon may be employed.
In the latter case the solution becomes sooner impoverished of metal and requires
replenishing by the addition of cobalt salt. It must be understood that I do not
bind myself to the above exact proportions: (nor to the exact method of bringing
the salts into solution) for I find by experiment that if either of the above solutions
is diluted by the addition of an equal quantity of water to half its strength it will
yield a good deposit of metal, but in that case a stronger current in proportion to
the surface of deposition, should be turned on from the dynamo or battery.
The best current-density I find to be not less than one ampere nor more than
four amperes per square foot of depositing surface, but a somewhat stronger current
may be advantageously employed during the first few minutes of deposition so as

page_text: to secure a rapid striking of the film on the surface, the current-density being
diminished so soon as the surface is once covered with a film.
The pieces to receive the deposit should be scrupulously cleansed and prepared in
the same well known manners as are usual for deposits of nickel, and they may
be polished after deposition in any of the ways known for polishing nickel-plated
goods.
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 :-
1. In the process of the electro-deposition of cobalt the use of magnesium salts in
the bath.
2. In the process of the electro-deposition of cobalt the combination with the salts
of cobalt or of cobalt and ammonium of salts of magnesium substantially as specified.
Dated this 22nd day of December 1887.
SILVANUS PHILLIPS THOMPSON.