Improvements in the Manufacture of White Lead.
Year: 1894

page_text: Date of Application, 10th Apr., 1894
Complete Specification Left, 10th Jan., 1895-Accepted, 16th Feb., 1895
PROVISIONAL SPECIFICATION.
Improvements in the Manufacture of White Lead.
I, ROWLAND MATTHEWS, of Bishopsgate Street Within, in the County of
London, Gentleman, do hereby declare the nature of this invention to be as
follows:-
This invention relates to the manufacture of white lead, and consists in a
development of the invention for which Letters Patent No. 20891 of 1892, were
granted to James Noad and myself, whereby I am enabled to obtain a pure
white lead in a state of minute division and possessed of great opacity, body and
covering power, by an improved procedure.
In carrying out the improved procedure, the litharge, massicot or lead monoxide
used is ground to a fine powder, which is mixed with water into a paste, which is
discharged into a suitable agitator.
The paste is therein subjected to the action of an aqueous solution containing
acetic acid and glycerine (which may advantageously be in the respective
proportions of about 14 lbs. each of the acetic acid and glycerine, say of the
respective strengths of 1038 and 1240, and about 104 lbs. of water to each
56 lbs. of the lead monoxide in the paste) for say 2 hours or more, during
which the mixture is continuously agitated, and after which the contents of the
agitator are drawn off and allowed to settle. When clear, the supernatant alkaline
liquor containing the basic acetate of the metal in solution is drawn off into a
clean tank, and the whole remainder of the charge is returned to the agitator to
contribute to the next charge, or may first be filter-pressed to recover any contained
liquor.
The clear liquor obtained as aforesaid, is then subjected to the action of a stream
of carbonic acid gas passed through it until the alkaline solution begins to turn
acid, which causes the basic acetate of the metal to be decomposed and precipitates
the white lead in an amorphous state of minute division especially suitable to the
wants of the painter and color maker.
The clear supernatant liquor is then drawn off from this tank, and the remaining
contents are filter-pressed to recover any contained liquor, the whole of such liquor
being returned to the agitator for re-use, and sufficient acetic acid and glycerine
(previously well mixed) being added to restore the solution in the agitator to its
original strength.
The cake of white lead obtained as aforesaid, is well washed in water to free it
as far as possible from any uncombined acetic acid and glycerine, after which it is
subjected to the action of a weak solution of ammonium or other suitable alkaline
carbonate, sufficient to neutralize any remaining acid, after which it is again
washed until every trace of the glycerine and ammonium or other alkaline acetate
is removed, after which it is again filter-pressed to remove as much moisture as
possible to facilitate the drying, which should be effected at the usual
temperature.
Dated this 10th day of April 1894
DAY, DAVIES & HUNT,
321, High Holborn, London, W.C., Agents for the Applicant.

page_text: improvements in the Manufacture of White Lead.
I, ROWLAND MATTHEWS, of Bishopsgate Street Within, in the County of
London, Gentleman, do hereby declare the nature of my said invention and in
what manner the same is to be performed to be particularly described and
ascertained in and by the following 'statement :--
This invention relates to the manufacture of white lead and further improvements
based upon the invention for which Letters Patent No. 20891 of the year 1892
were granted to James Noad and myself, whereby I am enabled to obtain a pure
white lead in a state of minute division and composed of great opacity, body and
covering power, by an improved procedure. By the invention protected by
Letters Patent No. 20891 of the year 1892, we were able to produce a valuable
commercial product which is of great value for purposes for which white lead is
applied, but I have since the date thereof discovered that by the use of my new
and improved process I can cheapen considerably the cost of manufacture, and
I am able to produce a white lead of a greater purity of colour and more suitable
than that manufactured under our former Patent when the white lead is required
for such purposes as for the production of a material of a pure white colour.
In carrying out my improved process, the massicot, litharge or other lead oxide
soluble in a mixture of acetic acid and glycerine is ground, as in our earlier
process, to a fine powder which is, either while dry or when mixed with water into
a paste, discharged into any suitable agitator which may be any convenient vessel
provided with means for intimately mixing and agitating the materials placed
therein.
After the powder or paste has been discharged into the agitator, I subject it, as
in our carlier process, to the action of an aqueous solution containing acetic acid
and glycerine. I find that the proportions which are most suitable for the purpose
of dissolving the lead oxide and forming the basic acetate of lead are about
14 lbs. each of acetic acid and glycerine, say of the respective strengths of 1,038
and 1,240; about 104 lbs. of water, and about 50 lbs. of oxide of lead. I allow
the solution to act upon the lead oxide for (say) an hour (or it may be less)
during the whole of which time the mixture is continuously agitated. I then draw
off the contents of the agitator into another tank and allow any particles which
may be suspended in the liquid to settle. I then draw off the clear supernatant
liquor, which contains basic acetate of lead, into a clean tank. I collect from the
settling tank all the deposited matter and if there be any undissolved oxide of lead
therein I return it to the agitator and I sometimes before doing so press it in a
filter-press in order to recover any of the contained liquor.
I treat the clear solution containing the basic acetate of lead with a stream of
carbonic acid gas which I pass through it until the solution turns acid; the action
of the carbonic acid gas is to throw down the white lead in an amorphous state
and very minutely divided and particularly suitable to the wants of the painter and
colour maker. After I have ceased to pass in the carbonic acid I allow the white
lead to settle and draw off from the tank. the supernatant liquor from which
practically the whole of the lead has been thrown down, and which contains in
solution glycerine and acetic acid.
:
Under our former Patent, we neutralized any acid in the solution before
removing the white lead after treatment with the carbonic acid gas, and thus
destroyed the free acetic acid. By my new and improved process, I am enabled to
use over and over again the clear liquid which remains in the tank after the white
lead has settled to the bottom of the tank, and all that is necessary is to make up
the strength of the acetic acid and glycerine to the proportions already indicated
and to use them over and over again in the agitator. In adding the acetic acid

page_text: and glycerine to make up the strength of the solution it is desirable to previously
well mix the acetic acid and glycerine together before adding them to the
solution.
After running off the clear liquid from the deposited white lead I filter-press
the white lead recovering as much of the liquor as possible. I then thoroughly
wash the white lead in any suitable manner to free it as far as possible from any
uncombined acetic acid and glycerine, and I then wash it with a weak solution of
ammonium carbonate or any suitable alkaline carbonate so as to neutralize any
remaining acid. I then thoroughly wash the white lead again until every trace of
the glycerine and ammonium acetate or any alkaline acetate or unaltered
ammonium carbonate or other alkaline carbonate is removed. I then again filter-
press the white lead to remove as much moisture as possible to facilitate the
drying.
The drying should be effected in the usual manner and at the usual
temperature.
Having now particularly described and ascertained the nature of the said inven-
tion and the manner in which the same is to be performed, I would have it
understood that I make no claim broadly to the use of acetic acid and glycerine
for the preparation of white lead, the use of which is protected under the said
earlier Patent, but I declare that what I seek to protect and claim as my
invention is;—
1. The improved process of manufacturing white lead by acting upon lead
oxides of the character herein before described with a solution containing glycerine
and acetic acid, separating the solution of lead acetate from all matters suspended
in the liquid, precipitating the white lead from the clear solution of lead acetate
with carbonic acid, running off the solution from which the white lead has been
deposited for further use in the agitator, neutralizing any free acid mixed with
the white lead with carbonate of ammonia or other suitable alkali, and finally
washing and drying the white lead, substantially as described.
2. In the manufacture of white lead by the action of a solution of acetic acid
and glycerine upon lead oxides of the character herein before described, the
improved process in which the clear solution of lead acetate is separated from any
undissolved and suspended matter and white lead is thrown down from the clear
solution with carbonic acid, substantially as described.
3. In the manufacture of white lead by the action of a solution of acetic acid
and glycerine upon lead oxides of the character herein before described, the improved
process in which the clear liquid from which the white lead has been precipitated
by carbonic acid is run off before any free acid which may be mixed with the
white lead is neutralized and the strength of the liquid is made up by the addition
of acetic acid and glycerine and the resultant liquid is used to act upon fresh
portions of lead oxide, substantially as described.
Dated this 10th day of January 1895.
DAY, DAVIES & HUNT,
321, High Holborn, London, W.C., Agents for the Applicant.