Improvements in the Manufacture of Basic Carbonate of Lead or White Lead.
Year: 1890

page_text: Date of Application, 27th Nov., 1890
Complete Specification Left, 26th Sept., 1891-Accepted, 31st Oct., 1891
PROVISIONAL SPECIFICATION.
Improvements in the Manufacture of Basic Carbonate of Lead or
White Lead.
We, WATSON SMITH, Lecturer in Chemical Technology, University College
London, and WILLIAM ELMORE, Electro-metallurgist, 47 Clapham Road, London,
do hereby declare the nature of this invention to be as follows:-
Our present invention relates to an improvement in the operation of the acetate
of ammonia process for making white lead or basic carbonate of lead, according to
the Specifications of MacIvor and others, No. 10426* of 18 July 1888, amended,
No. 6815 of 23rd April 1889, and MacIvor and Smith, No. 16,093 of October 10th,
1890, respectively, as well as in the operation of sundry other and older processes.
There are two disadvantages common to both of the first named processes and
these are:-
Firstly. That whereas a highly basic white lead or carbonate of lead is produced
in the earlier stages of the treatment with carbonic acid gas in the carbonating
vessel, of the basic acetate of lead produced by the subsequent treatment of the
oxide of lead (litharge or massicot) with acetate of ammonia, yet in the latter
stages of this process a much less basic carbonate of lead results owing to continued
action of carbonic acid on already formed basic carbonate of lead produced in the
carlier stages; and finally in the last stage, a product consisting of a mixture of
basic carbonate of lead with certain and varying proportions of normal carbonate
is produced, in which the latter carbonate reduces by dilution the body or covering
power of the former.
Though this disadvantage is much less marked in the case of the improved process
described by MacIvor and Smith No. 16093 of October 10th 1890, than in that of
Macl vor and others No. 10426* of 1888 and No. 6815 of 1889 before referred to
yet even in the former case it does exist to some extent.
Secondly. That the latter portions or fractions of white lead precipitated or
formed in the case of both processes above referred to, when the impurer and
cheaper forms of oxide of lead (litharge or massicot) are used containing besides
red lead also such impurities as copper, traces of iron, etc.-are not only of reduced
basicity but are also more or less coloured brownish or yellowish, and this
discolouration increases as the precipitation or carbonation process reaches its
conclusion.
The process by which we propose to avoid or overcome both these evils and to
obtain a product at once highly basic and of increased whiteness is the same in
principle both in the case of the process described in Specifications No. 10426*
of 1888; and No. 6815 of 1889 and in that of No. 16093 of October 10th 1890,
and this forms the gist of our invention.
We do not propose to carry on the carbonating process until all the lead is
converted from the state of basic acetate into carbonate, or all the ammonia is
re-converted into its acetate, but according to the circumstances and exigencies of
the process, we stop short of that final stage, when a basic carbonate both of
improved basicity and body and improved colour (whiteness) is obtained.
If the litharge were so pure that the final fraction of carbonated product is
white, though it lack basicity, a result determined by a previous laboratory test,―
then the liquors containing lead in solution as acetate, besides acetate of ammonia,
may be used over again to act upon fresh oxide of lead (litharge or massicot).
In most cases they will not entirely justify this course, since though slight and
gradual, there will be an accumulation of impurities tending to discolour a future
batch of white lead when produced.

page_text: It will then be best as a general rule to fully and separately precipitate or
carbonate the last fraction and thus obtain a purer acetate of ammonia for use over
again, than would be possible in the other cases. This of course must be done when
impurer oxide of lead (litharge or massicot) is used.
When impure litharge or massicot is used, yielding as final carbonated product
or final fraction of the carbonated product, a discoloured white lead or carbonate
of lead, then the tint of the latter fractions will serve as the criterion of the degree
of carbonation to adopt, in order by stopping at a certain stage the injection or
passing in of the carbonic acid gas, to obtain a white lead of the desired basicity
(covering power) and whiteness.
Since specimens of commercial oxide of lead (litharge or massicot), especially of
the cheaper and impurer kinds, differ in regard to the amount and proportions of
impurities contained, such for example as copper, traces of iron, etc. and so will
cause differences when the carbonating stage is reached, in the lengths to which
that process may be pushed in the forming a white lead of sufficient whiteness as
well as basicity, it is proposed to ascertain the point to which carbonation may be
carried, by a laboratory trial, which we make with an average sample of the
litharge or oxide of lead to be used, and a known weight of that sample. This is
treated with acetate of ammonia according either to process No. 10426* of 1888,
No. 6815 of 1889-or No. 16093 of October 10th 1890, and then fractionally
precipitated by carbonic acid gas, and the fractional precipitates so obtained, are
washed, drained and dried separately and then weighed and compared.
A classification can then be made as desired as a guide for the large scale
operations. The precipitates may also be tested as to the amount of basicity in a
suitable manner.
By the system of fractional precipitation of the basic carbonate, or fractional
carbonation of the basic acetate of lead whether partly dissolved and partly as a
magma in the case of process No. 10426* of 1888 or No. 6815 of 1889-or com-
pletely dissolved and separated from insoluble impurities as in the case of No. 16093
of October 10th 1890, so that by a sufficient degree of carbonating or passing in
of carbonic acid gas as already indicated, in a systematic manner, such a stage is
reached that a product or products of certain desired degrees of basicity and colour
are obtained, which may be suitably classified and utilized.
It is possible to obtain from an exceedingly impure litharge, a white lead of
greater basicity and covering power and of increased whiteness and purity over the
product obtainable by either of the processes above referred to.
We further propose to employ this fractional system of operating in such other
processes or known methods, as for example, those in which tribasic acetate of lead
is formed by the action of acetate of lead on oxide of lead (litharge) or acetic
acid on excess of litharge or oxide of lead or metallic lead with or without the
agency of heat, followed by treatment with carbonic acid gas.
In these cases also the tribasic acetate of lead formed first, converted by the
carbonic acid gas into basic carbonate of lead, is apt, by further and excessive
action of the carbonic acid, to be gradually reduced to mono-carbonate of lead, a
body as a pigment possessing but inferior covering power.
In some of the processes referred to, in which solutions of the tribasic acetate of
lead is possible, or is proposed, either in water or in solution of normal acetate of
lead or other suitable solvent, this fractional system would yield a white lead of good
basicity and whiteness. In others in which solution is not at once possible, as for
example where minute quantities of acetic acid or normal acetate of lead are
proposed to be used and caused to act upon an excess of litharge with heat or in
the cold, and in which carbonic acid (hot or cold) is collaterally passed in or
injected, giving rise thus to a detailed carbonation, the process of such fractional
precipitation as we propose to employ it, is practically out of the question.
Dated this 27th day of November 1890.

page_text: COMPLETE SPECIFICATION.
Improvements in the Manufacture of Basic Carbonate of Lead or
White Lead.
We, WATSON SMITH, Lecturer in Chemical Technology, University College,
London, and WILLIAM ELMORE, Electro-metallurgist, 51 Handforth Road,
Clapham Road, London, 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 present invention relates to an improvement in the operation of the acetate
of ammonia process for making white lead or basic carbonate of lead according to
the Specifications of MacIvor and others No. 10426* of 18th July 1888, amended;
No. 6815 of 23rd April 1889 and MacIvor and Smith, No. 16,093 of October 10th
1890 respectively, as well as in the operation of sundry other & older processes in
which acetate of lead primarily or secondarily acts as the solvent for the oxide of
lead (litharge or massicot) used, instead of acetate of ammonia.
There are two disadvantages to which both the first named processes are liable,
and these are:-
Firstly That whereas a highly basic white lead or carbonate of lead is produced
in the earlier stages of the treatment with carbonic acid gas in the carbonating
vessel, of the basic acetate of lead in the ammoniacal liquid, produced by the
previous treatment of the oxide of lead (litharge or massicot) with acetate of
ammonia, yet in the last stage of this process a much less basic carbonate of
lead results, owing to continued action of carbonic acid on already and especially
first formed basic carbonate of lead, and this is more likely to be the case when the
carbonic acid gas has been passed into the liquid too quickly. When this is the
case, a product consisting of basic carbonate of lead with certain and varying
proportions of normal carbonate, is produced, in which the latter carbonate reduces
by dilution the body and covering power due to the presence of the former.
Though this disadvantage is much less perceptible in the case of the improved
process described by MacIvor and Smith No. 16093 of October 10th 1890, than in
that of MacIvor and others No. 10426* of 1888 amended, and No. 6815 of 1889
before referred to, yet even in the former case it may exist to some extent, when
the carbonic acid gas is passed in in the carbonating process too quickly or in
excess.
Nevertheless the disadvantage referred to is greatly magnified, and requires
much greater care and precaution to avoid in those older white lead precipitation
processes in which acetate of lead is used primarily or secondarily for the solution
of the oxide of lead, or otherwise its conversion into basic acetate of lead prior to
carbonating, and in which no free alkali (ammonia) is present.
Secondly-That the latter portions or fractions of white lead precipitated or
formed in the case of both the processes first referred to, viz. MacIvor and others
(No. 10426 of 1888, amended, and No. 6815 of 1889) and MacIvor and Smith
No. 16093 of October 10th 1890, when the impurer and cheaper forms of oxide of lead
(litharge or massicot) are used containing besides red lead also such impurities as
copper and possibly minute traces of iron, etc., are not only of reduced basicity but
are also of a yellowish or brownish yellow tint which increases in depth from its
appearance in the earlier of the last stages of precipitation up to the final fraction
precipitated during the carbonating process.
The process by which we propose to avoid or overcome both these evils and to
obtain from a slightly cupreous litharge of lower and cheaper grade, or, in other
words, (and especially if we elect to prepare our own litharge from metallic
lead) from a cheaper form of, as being a less refined, metallic lead, a highly basic
white lead of great purity and whiteness, is the same in principle both in the case
of the process described in Specifications No. 10426* of 1888 amended, and

page_text: No. 6815 of 1889, and in that of No. 16093 of October 10th 1890, and this forms
the gist of our invention.
We do not propose to carry on the carbonating process until all the lead is
converted from the state of basic acetate into carbonate, or all the ammonia is
re-converted into its acetate, but according to the conditions of the process we stop
short of that final stage at a point in accordance with a previously or collaterally-
made test, and so as to obtain both a pure white and a highly basic product, free
from copper.
In addition, care is taken not to carbonate too quickly, and to slow
down the transmission of the gas towards the end of the process.
If the oxide of lead (litharge or massicot) be so pure that the final fraction of
carbonated product would be white, though it may lack basicity, a. result determined
by a previous laboratory trial, then the liquors furnished after filtration from the
white lead prepared with the precaution above described, and containing lead in
solution as acetate besides acetate of ammonia, may be used over again to act upon
fresh oxide of lead (litharge or massicot).
In certain cases their condition will not entirely justify this course, since though
slight and gradual, there will be an accumulation of impurities tending to discolour
a subsequent batch of white lead when produced. It will then be best to fully and
separately precipitate or carbonate the last portions of lead in the filtrate liquors,
and thus obtain a more pure acetate of ammonia for use over again, than would be
otherwise obtained.
This of course will be the plan that must be adopted at the proper stage of the
circulatory process when impure oxides of lead (litharge or massicot) are used.
In such case, the tint of the latter fraction produced on carbonating with the
precautions given, together with its degree, and the proportion of the fraction so
contaminated, will serve as the criterion of the degree of carbonating to adopt so as
to obtain a white lead both of the desired whiteness and basicity.
Since specimens of the cheaper oxide of lead (litharge or massicot) or otherwise
of metallic lead from which the oxide is made, differ in regard to the amount of
copper and other slight impurities they contain, it is best to determine upon an
average sample and a known weight thereof by a laboratory trial how far the
carbonating process may proportionately be pushed (observing the precautions
given above) for the obtainment of a good product. Such oxide of lead is treated with
acetate of ammonia according, as the case may be, to process No. 10426* of 1888,
amended, or No. 6815 of 1889, or No. 16093 of October 10th, 1890, and then
fractionally precipitated by carbonic acid gas and the fractional precipitates so
obtained are washed, drained and dried separately and then weighed and compared
by suitable tests. A practical classification can then be made as desired and will
form a guide for the large scale operations, carried out on similar lines.
By this operation of fractional precipitation of the basic carbonate or fractional
carbonating of the basic acetate of lead in presence of more or less ammonia, in the
cases of the processes covered by Patents as above named similar advantages are
obtained as already described, though in a less degree, and to a more limited
extent, in the case of process No. 10426* of 1888, amended, and No. 6815 of 1889
than in that of process No. 16093 of October 10th 1890, since a little residual
copper is apt in the case of the use of a cheaper and cupreous oxide of lead
(litharge or massicot) in the former processes, to remain in the matters comprised
in the white lead and to soon or gradually develop a yellowish tint, whereas in the
case of process No. 16093 of October 10th 1890, where all insoluble and residual
matters contained in the commercial oxide of lead are separated by filtration, and
only the clear solution carbonated, the improved system of treatment by fractional
carbonating is under perfect control.
Indeed by this latter process as thus improved, it is possible to obtain from an
exceedingly impure specimen of litharge (ie. rich in copper) a white lead of great
basicity, purity, and brilliant whiteness, whilst in the case of any other precipitation
process whatever, including No. 10426* of 1888, amended, and 6815 of 1889, such a
result with such material, would be entirely out of the question.

page_text: In the case of those earlier and already well known processes in which oxide
of lead (litharge or massicot) is dissolved as the tribasic acetate by treatment hot
or cold with solutions of normal acetate of lead, and the clear solution, suitably
separated from the residue, and consisting substantially of a solution of tribasic
acetate of lead in water or solution of normal acetate of lead, is carbonated by
carbonic acid gas, if the oxide of lead was of cupreous character, the white lead
produced will be of yellowish tint, from contamination with small quantities of
copper. But we have discovered that whilst in absence of ammonia and carbonate
of ammonia our fractional process of carbonating is effective to a more limited
extent than when the acetate of ammonia processes already described and named, are
employed, yet it is effective in the case of minute quantities of copper, the presence
of which would be sufficient otherwise to condemn an oxide of lead. By rejecting,
on carbonating, a still larger final fraction, i.e. accepting a smaller first fraction
of carbonated product than would be possible in the acetate of ammonia processes,
we have found that the copper is not precipitated, but remains among the lead
acetates left dissolved in the liquors whilst a white and basic product (white lead)
is precipitated.
The precautions of slowly carbonating and especially of slackening the trans-
mission of gas towards the close, are now specially observed. This peculiar
yellowish cupreous compound is thus only precipitated in the later fractions by
carbonic acid, though at an earlier stage and much more easily than when ammonia
and ammonium carbonate are present, and we propose to make use of this fact, in
preparing and manufacturing white lead from oxides of lead (litharge or massicot)
containing copper, which hitherto owing to such presence of copper, could not be
employed for the production of a white product.
Having now particularly described and ascertained the nature of our said inven-
tion and in what manner the same is to be performed, we declare that what we
claim is :-
Firstly. The improvement in the manufacture of white lead by the acetate of
ammonia processes as described, viz. by the methods patented as No. 10426* of
July 18th 1888, amended, and No. 6815 of April 23rd 1889, and No. 16,093
of October 10th 1890, whereby a partial or fractional precipitation of the white
lead by carbonic acid is adopted, as described, and with the precautions described,
so as to secure the formation of a more highly basic carbonate of lead or white
lead, than could be obtained in the ordinary way.
Secondly. The improvements in the manufacture of white lead from oxide of
lead (litharge or massicot) containing copper, by the acetate of ammonia processes
as described and cited, whereby a partial or fractional precipitation of the white
lead by carbonic acid is adopted as described and with the precautions described,
so as not only to secure the formation of a carbonate of lead of high basicity but
so as to avoid the co-precipitation with this white lead of any copper present, thus
causing its discolouration.
Thirdly. The improvement in the manufacture of white lead by the earlier and
already known acetate of lead precipitation processes, as described, and using an
oxide of lead (litharge or massicot) containing small quantities of copper, whereby
a partial or fractional precipitation of the white lead by carbonic acid with the
precautions given, is adopted as described, so as not only to secure the formation
of a carbonate of lead of improved basicity, but more particularly to avoid the
co-precipitation with it of any copper, which would cause discolouration of it.
Dated this 24th day of Sentember 1891
WATSON SMITH.
WILLIAM ELMORE.