Improvements in the Manufacture of White Lead.
Year: 1891

page_text: Date of Application, 12th May, 1891-Accepted, 11th July, 1891
COMPLETE SPECIFICATION.
[Communicated from abroad by ELLERT WALLENDAHL DAILL, of 71, Broadway,
in the City and State of New York, United States of America, Chemist.]
Improvements in the Manufacture of White Lead.
1
".
I, HENRY HARRIS, LAKE, of the firm of Haseltine,, Lake & Co., Patent
Agents, 45 Southampton Buildings, in the County of Middlesex, 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:-
The process which I have invented consists substantially in exposing metallic
lead to the successive action of acetic acid and air preferably heated whereby the
surface of the lead is oxidized and converted into basic acetate of lead, dissolving
and removing such acetate by means of dilute acetic acid, which not only removes
the basic acetate but attacks the metallic lead formning neutral, acetate of lead, and
then decanting the solution or mixture of basic and neutral acetate so formed and
mixing it with a carbonate of an alkali, such as the carbonate of soda, whereby
carbonate of lead is formed as a precipitate.
".
In carrying out my invention in the manner I have found most practicable, the
metallic lead in the form of strips of sheets, but preferably in the form known as
"feathers," is packed in a suitable corroding tank or corroder, and in order to
expose as much of the surface of such sheets or strips as possible, it is preferable to
arrange them vertically in the vessel. Dilute acetic acid is then poured or sprinkled
upon the lead and when the surface of the strips or sheets is wet with-the acid, hot
water is poured upon the lead, or preferably a jet of steam is passed through the
corroder a few seconds, to heat the acid and accelerate its action. The corroder is
then opened and a blast of air preferably heated is forced through it for a sufficient
time to permit the lead to absorb as much oxygen as it will take up. From one to
four hours will usually be sufficient for this purpose depending upon the temperature
of the air blast and the condition of the atmosphere, when the surface of the lead
will become thoroughly oxidized and present a whitish appearance. Dilute acetic
acid is then poured through the lead which washes off and dissolves the coating of
basic acetate of lead formed on the surface of the strips or feather's and also attacks
the metallic lead forming neutral acetate of lead which goes into the solution with
the basic acetate. The solution thus formed is a mixture of basic and "neutral
acetates of lead. It is important that the acid used for this part of the process
should be very dilute, the acid forming from about five to ten per cent. of the
liquor. The combined solution or mixture, thus obtained is decanted off and the
metallic lead remaining in the vessel is again subjected to the blast of air, sufficient
acid usually remaining upon its surface to cause it to be oxidized by the air, and
this process is continued until the metallic lead is all converted into acetates and
carried off in the solution as described. This part of the process may be a continuous
one, fresh metallic lead being added above as that below is consumed, and, after the
process is first started, fresh acid is added from time to time only as required.
When the combined acetate solution has attained a sufficient density, it is drawn off
into a settling tank where it is allowed to remain until such brown oxide and other
impurities as may be contained in it have settled to the bottom of the tank. The
clear solution remaining is then decanted off into a precipitating tank where it is
stirred briskly and a suitable carbonate of an alkali, such as the carbonate of soda
preferably in the anhydrous solid form, is added in a sufficient quantity to decompose
the acetates and precipitate the lead in the form of basic carbonate of lead. The
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page_text: liquid of the solution is then drawn off and the precipitate is thoroughly washed with
water to dissolve and remove any free alkali remaining in it.
The basic carbonate of lead so obtained is treated and prepared for use in the
manner ordinarily employed for that purpose.
Instead of sprinkling the metallic lead with acetic acid after it is placed in the
corroder, it may be passed through a trough filled with dilute acid instead of water
in the process of converting it into feathers, and the feathers so treated may be
packed in the corroder and the blast of air applied at once without applying hot
water or steam.
If desired, the acetic acid may be put in the corroder in an undiluted form and be
diluted and brought into contact with all parts of the surface of the lead by the
subsequent introduction of hot water or steam, which will then have the function of
diluting the acid as well as of heating it and hastening the process. I prefer to
make use of heated air for oxidizing the lead because it shortens the process. very
materially; and for the same reason I prefer to use a blast rather than to depend on
the mere exposure of the lead to the atmosphere.
My improved process is much more rapid and economical than those heretofore
employed, the materials and reagents used are cheap and readily obtainable and the
product is amorphous in structure and superior in quality to that obtained by the
ordinary processes heretofore in use. It is exceedingly white, spongy, and so friable
that it can be reduced to an impalpable powder by simple pressure of the finger: it
grinds perfectly in linseed oil, is soluble without residuum in acetic acid, in which
solution it is precipitated by oxalic acid in the same form as the highest standard
white lead heretofore produced, and is free from foreign substances.
When ground
in linseed oil, and afterwards diluted with turpentine,, it holds in suspension for
a long time, a feature which is particularly desirable in the manufacture of mixed
paints.
In the manufacture of chrome yellow and chrome green by the German process
it produces a very brilliant color, as is also the case in the manufacture of artificial
vermilion of a purple tint in which, when mixed with orange mineral as its basis
and precipitated simultaneously with cosinate of lead, it gives a peculiar brightness
to the red which otherwise could only be obtained from oxide of zinc. It is
especially useful as a pigment on account of its great staining and covering
properties, which are due to the large proportion of hydrated oxide present in its
composition.
I obtain this superior product by my new process, which is cheap, simple and
rapid, whereas to obtain an equally good result by older methods would involve so
much time, labor and expense that the cost of manufacture would be practically
prohibitive of its use except for special and restricted purposes..
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed as communicated to me by
my foreign correspondent I declare that what I claim is :-
1.. The process of making white lead which consists in forming a combined
.solution of basic acetate of lead and neutral acetate of lead by exposing metallic
lead to the successive action of dilute acetic acid and air and then precipitating the
said basic and neutral acetates in the form of basic carbonate of lead by means of a
carbonate of an alkali; substantially as described.
2. The process of making white lead which consists in exposing metallic lead to
the alternate and successive action of dilute acetic acid, and hot air, whereby a
solution of basic and neutral acetates of lead is formed, decanting and clarifying
such solution, and finally precipitating basic carbonate of lead from said basic and
'neutral acetates by adding to the solution a suitable carbonate of an alkali ;
substantially as described.
3. The process of making white lead which consists in exposing metallic lead, to
the alternate and successive action of hot diluted acetic acid and hot air whereby a

page_text: solution of basic and neutral acetates of lead is formed and precipitating basic
carbonate of lead from such solution by adding thereto a suitable carbonate of an
alkali, substantially as described.
Dated this 12th day of May 1891
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.