Improvements in the Manufacture of White Lead for use as a Pigment.
Year: 1892

page_text: Date of Application, 22nd Apr., 1892
Complete Specification Left, 21st Jan., 1893-Accepted, 4th Mar., 1893
PROVISIONAL SPECIFICATION.
Improvements in the Manufacture of White Lead for use as a
Pigment.
We, ELWYN WALLER, Professor of Chemistry, and CHARLES AUGUSTUS
SNIFFIN, Mining Engineer, both of the School of Mines, Columbia College, in
the City, County and State of New York, United States of America, do hereby
declare the nature of this invention to be as follows:-
This invention relates to precipitation processes of making white lead for use as
a pigment, and particularly to that method wherein a solution of basic lead acetate
is treated with carbon dioxide for the precipitation of a portion of the lead in the
solution in the form of a hydrocarbonate.
In carrying out our invention, we first prepare a solution of basic lead acetate,
and then mix the solution with water charged with carbon dioxide. The carbon
dioxide precipitates some portion of the lead in the solution in the form of highly
amorphous lead hydrocarbonate, which has special advantages as a pigment, in
respect of "body" and smoothness, over the hydrocarbonate precipitated, according
to old methods, by carbon dioxide in the form of gas.
We sometimes force carbon dioxide gas under pressure into the mixture of
carbonated water and solution of basic lead acetate, the liquid being in a closed
vessel. The effect of this treatment is to produce a greater percentage of the
precipitate in proportion to the volume of water in the precipitating vessel; this
being of material advantage where the residual liquor from the precipitation
(containing neutral lead acetate) is to be employed in preparing a fresh charge of
the solution of basic lead acetate.
The two important features of our invention are, first, the use of carbonated
water for precipitating, whereby the amorphous character of the precipitate is
assured; and secondly, precipitation with the aid of carbon dioxide under a
pressure above that of the atmosphere, and preferably at a pressure of from 5 to
10 pounds to the square inch, in order to effect the maximum of precipitation with
the minimum of water in the residual liquor.
Dated the 22nd day of April 1892.
G. G. M. HARDINGHAM,
191, Fleet Street, London, E.C., Chartered Patent Agent.
COMPLETE SPECIFICATION.
Improvements in the Manufacture of White Lead for use as a
Pigment.
We, ELWYN WALLER, Professor of Chemistry, and CHARLES AUGUSTUS
SNIFFIN, Mining Engineer, both of the School of Mines, Columbia College, in the
City, County and States of New York, United States of America, 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:-
This invention relates to what are known as precipitation processes, as dis-
tinguished from corrosion processes, for producing white lead.
22
In the preparation of lead hydrocarbonate, commercially known as the pigment
"white lead," one of the processes is called the "French"
"
or precipitation
method. It consists in obtaining a solution of basic acetate of lead, and then
passing through this solution under ordinary atmospheric pressure a current of
Die 27

page_text: carbon dioxide gas, which effects the precipitation of a portion of the lead in the
solution as
"white lead." The character of the product obtained by this "French"
method is thus described in "Die Erd-Mineral-und Lack-Farben, etc., Vierte
Auflage, Weimar, 1881; Dr. Stanislaus Mierzinzinski," page 75 - One obtains
by this method a white lead which, it is true, is of a particularly fine white colour,
but has very little covering power, because the same is of a loose texture, of a
coarse grain, and often crystalline."
"5
The present method of managing this precipitation affords a product which is
highly amorphous in character, and possesses in a marked degree the covering
power and body so much desired in white lead for use as a pigment; a very
material economy in the manufacture being moreover effected.
In carrying out our invention, we first prepare a solution of basic lead acetate,
and then mix the same with water, preferably impregnated with carbon dioxide.
Into this mixture, carbon dioxide gas is passed under pressure; the mixture being
at the same time agitated so that the necessary amount of gas may be taken up.
The lead, over and above that which the acetic acid will hold in combination
under these conditions, is separated and precipitated in the form of lead hydro-
carbonate.
in
A pressure of from 8 to 10 pounds per square inch in the closed precipitating
vessel will suffice for the purpose, but we do not limit ourselves to this range of
pressures. We have found that, under ordinary atmospheric pressure, that is,
an open vessel, the other conditions being as described above, a precipitate of the
same quality is produced, but that the amount of precipitated lead hydrocarbonate
obtainable under such circumstances depends largely upon the degree to which the
solution of basic acetate is diluted. In other words, under ordinary atmospheric
pressure, the greater the dilution, the larger the percentage of the lead hydro-
carbonate which can be precipitated by carbon dioxide gas. "By employing carbon
dioxide under pressure in the precipitating vessel or tank, the necessity for great
dilution is avoided, and the lead acetate solution whence the hydrocarbonate has
been precipitated does not require so much fuel to bring it to that state of con-
centration in which it is suitable for use in preparing another portion of basic lead
acetate by, for example, boiling it with litharge, or other substance containing
lead.
It will be understood by those familiar with the art that the solution of basic
lead acetate to be acted upon by carbon dioxide is produced by treating some
substance containing lead, as litharge for example, with a solution of neutral lead
acetate obtained in the process of manufacture from a preceding precipitating
operation; and the success of the method, from a commercial or economical point
of view, is dependent on the degree to which this solution of neutral acetate is
diluted. Hence the importance of the treatment with carbon dioxide under a
pressure above that of the atmosphere, as it practically enables the maximum of
precipitated hydrocarbonate to be obtained with the minimum of dilution.
We do not broadly claim herein the mixing of the solution of basic lead acetate
with carbonated water in order to obtain a highly-amorphous product, as such is
referred to in the Specification to our Letters Patent dated 9 Dec., 1891,
No. 21,545.
The method described in the Specification to the said Letters
Patent may be employed with special advantage in connection with our present
invention; the latter effecting an important economy. We may, however, use
the carbon dioxide gas under pressure, in accordance with this invention, in
connection with the well-known "French" method, heretofore described, with
results that show an improvement in the product as well as a decrease in the cost
of production.
The precipitating tank or vessel containing the solution of basic acetate must of
course be closed in order that the requisite pressure may be obtained therein. We
have not, however, considered it necessary to show any apparatus for carrying out
our invention, as appliances suitable for the purpose will be within the knowledge
of any one skilled in the art.

page_text: Having now particularly described and ascertained the nature of this invention
and in what manner the same is to be performed, we claim :-
--
1. The herein-described method of making white lead, which consists in sub-
jecting a solution of basic lead acetate with water to the action of carbon dioxide
gas while the solution is under a pressure above that of the atmosphere, and
maintaining such pressure during precipitation of lead in the form of hydro-
carbonate from the said solution.
2. The herein-described method of making white lead, which consists in sub-
jecting a solution of basic lead acetate mixed with water impregnated with carbon
dioxide while the mixture is under a pressure above that of the atmosphere and in
mass to the action of carbon dioxide gas, and maintaining such pressure during
precipitation of lead in the form of lead hydrocarbonate from the said solution.
3. The herein-described method of making white lead, which consists in sub-
jecting a solution of basic lead acetate mixed with water impregnated with carbon
dioxide while the mixture is in mass and under a pressure above that of the atino-
sphere to the action of carbon dioxide gas, and agitating the said mixture during
the passage of the gas therethrough, such pressure being maintained during
precipitation of lead in the form of lead hydrocarbonate from the solution.
Dated the 20th day of January 1893.
G. G. M. HARDINGHAM,
191, Fleet Street, London, E.C., Chartered Patent Agent.