Improvements in Making White Lead.
Year: 1897

page_text: Date of Application, 17th Apr., 1897
Complete Specification Left, 15th Jan., 1898-Accepted, 5th Mar., 1898
Improvements in Making White Lead.
I, JOHN STEWART MACARTHUR, of 589, Shields Road, in the County of Glasgow,
North Britain, Technical Chemist, do hereby declare the nature of this invention
to be as follows, that is to say:-
My said invention relates to the process for making white lead described in my
Patent Specification No. 9,655 of 1894, and has for its object to improve that
process.
A solution of lead tartrate having been formed as described in my said
specification, I, by my present invention add ammonia thereto before treating it
with carbonic acid; and I thereby obtain a better quality of white lead, and
minimise the amount of lead tartrate in the precipitate of white lead. This result
is obtained even in comparatively strong solutions originally containing as much
as 6 per cent. of Rochelle salt, with an equivalent of lead oxide dissolved therein.
The addition of a minute quantity of ammonia has been found very beneficial;
and the best results seem to be obtained by the use of a quantity of ammonia slightly
in excess of the chemical equivalent of the lead dissolved. When ammonia is
present the temperature of the liquid need not approach boiling point; and satis-
factory precipitations have been obtained with a temperature of 180 degrees
Fahrenheit.
After precipitation the solution is liable to contain an excess of carbonic acid,
which should by preference be removed prior to a succeeding operation as it inter-
feres with the dissolving of the lead oxide. To obviate this inconvenience and
to render the tartrate solution available for immediate application to lead oxide,
the best plan is to avoid an excess of carbonic acid by stopping the supply of it
immediately at or just before the point of complete saturation is reached. It can,
however, be removed by carefully adding some fresh lead tartrate in quantity
sufficient to absorb the excess.
Dated this Sixteenth day of Anil 1907
EDMUND HUNT,
Applicant's Agent.

page_text: and in what manner the same is to be performed, to be particularly described and
ascertained in and by the following statement, that is to say:
-
My said invention relates to the process for making white lead described in my
Patent Specification No. 9655 of 1894, and has for its object to improve that
process.
A solution of lead tartrate having been formed as described in my said
specification, I, by my present invention add ammonia thereto before treating it
with carbonic acid; and I thereby obtain a better quality of white lead, and
minimise the amount of lead tartrate in the precipitate of white lead. This result
is obtained even in comparatively strong solutions originally containing as much
as 6 per cent. of Rochelle salt, with an equivalent of lead oxide dissolved therein.
The addition of a minute quantity of ammonia has been found very beneficial;
.and the best results seem to be obtained by the use of a quantity of ammonia slightly
in excess of the chemical equivalent of the lead dissolved. When ammonia is
present the temperature of the liquid need not approach boiling point; and satis-
factory precipitations have been obtained with a temperature of 180 degrees
Fahrenheit.
After precipitation the solution is liable to contain an excess of carbonic acid,
which should, by preference be removed prior to a succeeding operation as it inter-
feres with the dissolving of the lead oxide. To obviate this inconvenience and
to render the tartrate solution available for immediate application to lead oxide,
the best plan is to avoid an excess of carbonic acid by stopping the supply of it
immediately at or just before the point of complete saturation is reached. It can,
however, be removed by carefully adding some fresh lead tartrate in quantity
sufficient to absorb the excess.
Having now particularly described and ascertained the nature of my said in-
vention and in what manner the same is to be performed, I declare that what I
claim is :-
The process of making white lead, in which lead oxide is dissolved in a solution
of a tartrate of soda or of potash or of a mixture of these alkalies or of the double
tartrate known as Rochelle salt" at or about a boiling temperature, and in
subsequently adding ammonia to the lead tartrate thus formed then treating the
liquid with carbonic acid during which latter treatment the temperature may be
less than the boiling point substantially as herein before described.
Dated this Fourteenth day of January 1898.
EDMUND HUNT,
Applicant's Agent.