IMPROVEMENTS IN THE MANUFACTURE OF WHITE LEAD
Year: 1875

page_text: LETTERS PATENT to Edward Milner, of Springfield, Warrington, in
the County of Lancaster, Salt Manufacturer, for the Invention of
"IMPROVEMENTS IN THE MANUFACTURE OF WHITE LEAD.”
Sealed the 21st January 1876, and dated the 22nd November 1875.
PROVISIONAL SPECIFICATION left by the said Edward Milner at
the Office of the Commissioners of Patents, with his Petition, on
the 22nd November 1875.
I, EDWARD MILNER, of Springfield, Warrington, in the County of
Lancaster, Salt Manufacturer, do hereby declare the nature of the said.
Invention for "IMPROVEMENTS IN THE MANUFACTURE OF WHITE LEAD," to be
as follows:
My Invention relates to an improved method of manufacturing
"white lead" carbonate of lead from litharge, and is a further improve-
ment on the processes described in the Specifications of Letters Patent-
granted to John Gallemore Dale and myself, the said Edward Milner,
dated August 10th 1869, No. 2443, and also to myself, the said Edward ·
Milner, dated June 22nd.1872, No. 1881.

page_text: My improvements relate more especially to the Patent of June 22nd
1872, and consist in certain alterations discovered in the course of
manufacture, by which I have been enabled to produce a carbonate of
lead equal in commercial value to most of that produced by the well
known "Dutch method," and of a quality far superior to that which
I have found it possible to make by accurately following my former
Specification.
I now proceed to describe these my improvements :- -I take oxide of
lead, commonly known as litharge, in a very finely ground state, and
mix it with a solution of chloride of sodium, potassium, or ammonium,
in the proportion of about 4lbs. dry litharge to 1lb. dry salt, the salt
being dissolved in 16 parts by weight of water. I do not consider these
precise proportions essential, but they are what I find work satisfactorily.
This mixture is now agitated thoroughly in a wooden pug mill, which
is best made of yellow pine, with arms of American elm, driven by
suitable machinery. Oak timber must on no account be introduced
into this vessel or the proper reaction will not take place. The agitation
should be kept up for at least 3 hours without ceasing, because if it is
stopped the whole mass will set so stiff that it cannot be further agitated
but has to be removed by hand from the mill. After this time the
mixture becomes more fluid, and only requires agitating a short time to
finish the charge; but this time can only be found by actual examin-
ation of each charge. I usually work the charges for about 4 hours.
The result of this operation is an insoluble basic chloride of lead
(previously described in the Specification of the Patent No. 1881, of
1872, as hydrated oxide and chloride of lead), and it is the equivalent
of what is referred to in the Specification of the Patent of August 16th
1869, as being insoluble basic salts of lead; the chloride. will be
suspended in a solution, which will contain caustic soda and common
salt (when chloride of sodium is used). Up to this point I am merely
setting forth the improvements made on the part of the Invention, the
subject of the Patent of 1869, No. 2443, namely, this particular way of
making the insoluble basic salt of lead and effecting its combination
with caustic soda in one operation. The mixture thus made is now
introduced into a vessel lined with lead and fitted with wooden beaters,
fitting the vessel rather higher than the horizontal shaft to which the
beaters are fixed, and therefore leaving one arm of the beaters always
above the surface, so as to obtain as great an amount of agitation aș

page_text: possible. A steam of carbonic acid gas is now introduced to effect the
result referred to in the said Patent of 1869, but it should be introduced
as described in the Specification of the Patent of 1872, that is, near the
bottom or at a low part of the vessel.
The action of the carbonic and gas will be much more effective and
a better result will I find be produced if instead of arresting it at the
point mentioned in the said Specification of the Patent of 1872 it is
continued beyond that point where the solution no longer gives an
alkaline reaction. By thus continuing to force the currents of carbonic
acid gas into the mixture for a longer time than was proposed in my
former Specification, varying it according to the violence of agitation
and strength of the gas from /, an hour to about 3 hours, the resulting
carbonate of lead will be obtained of an improved character, and of far
greater commercial value than what I have heretofore obtained, being
denser, having more body, and working better as a pigment. Care.
must be taken not to continue the action of the carbonic acid gas for
too long a time, as in that case it would lose its value as a pigment.
I have discovered a very simple test by which any one can tell when
it is necessary to cease supplying gas to the mixture. When the
solution has ceased to shew an alkaline reaction the mixture is a viscid
homogeneous mass, and if a portion is shaken in a half empty glass it
will coat the sides and remain in a layer all over them; but when
sufficient gas has been applied a small quantity shaken in a clear glass
vessel it coats the sides with a very thin layer like frost on a window
pane, and after standing for a few seconds the clear liquid separates
from the carbonate of lead and leaves an arborescent pattern on the
interior of the glass. If however the action of the gas is continued for
too long a time the product loses its value, becoming like sand, and not
coating the test glass at all, but settling rapidly out of the salt solution.
The workmen can tell by this simple test to the greatest nicety when to
stop the supply of gas. The carbonate of lead thus produced after being.
washed to free it from salt and being dried is ready for use, and is of
greatly improved quality, as previously described.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said Edward Milner in the Great Seal Patent Office on
the 19th May 1876.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, EDWARD
MILNER, of Springfield, Warrington, in the County of Lancaster, Salt
Manufacturer, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Twenty-second day of November, in
the year of our Lord One thousand eight hundred and seventy-five, in
the thirty-ninth year of Her reign, did, for Herself, Her heirs and suc-
cessors, give and grant unto me, the said Edward Milner, Her special
license that I, the said Edward Milner, my executors, administrators,
and assigns, or such others as I, the said Edward Milner, my exe-
cutors, administrators, and assigns, should at any time agree with, and
no others, from time to time and at all times thereafter during the term
therein expressed, should and lawfully might make, use, exercise, and
vend, within the United Kingdom of Great Britain and Ireland, the
Channel Islands, and Isle of Man, an Invention for "IMPROVEMENTS
IN THE MANUFACTURE OF WHITE LEAD," upon the condition (amongst
others) that I, the said Edward Milner, my executors or admini-
strators, by an instrument in writing under my, or their, or one of
their hands and seals, should particularly describe and ascertain the
nature of the said Invention, and in what manner the same was to
be performed, and cause the same to be filed in the Great Seal Patent
Office within six calendar months next and immediately after the date
of the said Letters Patent.
NOW KNOW YE, that I, the said Edwar Milner, do hereby
declare the nature of the said Invention, and in what manner the
same is to be performed, to be particularly described and ascertained
in and by the following statement thereof, that is to say :-
My Invention relates, to an improved method of manufacturing
"white lead," carbonate of lead from litharge, and is a furthur improve-
ment on the processes described in the Specifications of Letters Patent
granted to John Gallemore Dale and myself, the said Edward Milner,
dated August 10th 1869, No. 2443, and also to myself, the said Edward
Milner, dated June 22nd 1872, and No. 1881.

page_text: My improvements relate more especially to the Patent of June 22nd.
1872, and consist in certain alterations discovered in the course of
manufacture, by which I have been enabled to produce a carbonate of
lead equal in commercial value to most of that produced by the well
known "Dutch method," and of a quality far superior to that which I
have found it possible to make by accurately following my former
1872, and consist in certain alterations discovered in the course of
manufacture, by which I have been enabled to produce a carbonate of
lead equal in commercial value to most of that produced by the well
known "Dutch method," and of a quality far superior to that which I
have found it possible to make by accurately following my former
Specification.
I now proceed to describe these my improvements :-I take oxide of
lead, commonly known as litharge, in a very finely ground state and
mix it with a solution of chloride of sodium, potassium, or ammonium,
in the proportion of about 4lbs. dry litharge to 1lb. dry salt, the salt
being dissolved in 16 parts by weight of water. I do not consider these
precise proportions essential, but they are what I find work satisfactorily.
This mixture is now agitated thoroughly in a wooden pug mill, which
is best made of yellow pine, with arms of American elm, driven by
suitable machinery. Oak timber must on no account be introduced
into this vessel or the proper reaction will not take place. The agitation
should be kept up for at least three hours without ceasing, because
if it is stopped the whole mass will set so stiff that it cannot be further
agitated, but has to be removed by hand from the mill. After this time
the mixture becomes more fluid, and only requires agitating a short
time to finish the charge; but this time can only be found by actual
examination of each charge. I usually work the charges for about
4½ hours. The result of this operation in an insoluble basic chloride of
lead (previously described in the Specification of the Patent No. 1881,
of 1872, as hydrated oxide and chloride of lead), and it is the equivalent
of what is referred to in the Specification of the Patent of August 16th
1869, as being insoluble basic salts of lead; the chloride will be
suspended in a solution which will contain caustic soda and common
salt. When chloride of sodium is used up to this point I am merely
setting forth the improvements made on part of the Invention, the
subject of the Patent of 1869, No. 2443, namely, this particular way of
making the insoluble basic salt of lead, and effecting its combination
with caustic soda in one operation. The mixture thus made is now
introduced into a vessel lined with lead and fitted with wooden beaters,
filling the vessel rather higher than the horizontal shaft to which the
beaters are fixed, and therefore leaving some of the arms of the beaters
always above the surface, so as to obtain as great an amount of agitation

page_text: as possible. A stream of carbonic acid gas is now introduced to effect
the result referred to in the said Patent of 1869, but it should be intro-
duced as described in the Specification of the Patent of 1872, that is,
near the bottom or at a low part of the vessel.
The action of the carbonic acid gas will be much more effective, and
a better result will I find be produced if instead of arresting it at the
point mentioned in the said Specification of the Patent of 1872 it is
continued beyond that point when the solution no longer gives an
alkaline reaction. By thus continuing to force the current of carbonic
acid gas into the mixture for a longer time than was proposed in my
former Specification, varying it according to the violence of agitation
and strength of the gas from an hour to about 3 hours, the resulting
carbonate of lead will be obtained of an improved character, and of far
greater commercial value than what I have heretofore obtained, being
denser, having more body, and working better as a pigment. Care
must be taken not to continue the action of the carbonic acid gas for
too long a time, as in that case it would lose its value as a pigment.
I have described a very simple test by which any one can tell when
it is necessary to cease supplying gas to the mixture. When the solution
has ceased to show an alkaline reaction the mixture is a viscid homo-
geneous mass, and if a portion is shaken in a half empty glass it will
coat the sides and remain in a layer all over them; but when sufficient
gas has been applied a small quantity shaken in a clear glass vessel it
coats the sides with a very thin layer like frost on a window pane, and
after standing for a few seconds the clear liquor separates from the
carbonate of lead and leaves an arborescent pattern on the interior of
the glass. If however the action of the gas is continued for too long a
time the product loses its value, becoming like sand, and not coating
the test glass at all, but settling rapidly out of the salt solution. The
workmen can tell by this simple test to the greatest nicety when to stop
the supply of gas. The carbonate of lead thus produced after being
washed to free it from salt, and being dried, is ready for use, and is of
greatly improved quality as compared to that produced by the former
method, as previously described.
Having now described my Invention, and the best means I am
acquainted with for carrying the same into effect, I claim,―
The imprated method of manufacturing the insoluble hosia

page_text: salt of lead in a solution of caustic soda at one operation, substantially
as described.
Secondly. The improved method of completing the manufacture of
carbonate of lead by converting a mixture such as is obtained by the
improved method referred to in the first claiming clause by treating it
with a stream of carbonic acid gas beyond the point at which it ceases
to show an alkaline reaction, and by employing the characteristic test
as described in order to indicate the proper point of saturation, sub-
stantially as described.
Thirdly. The manufacture, substantially as described, of carbonate of
lead of an improved quality by employing relatively large quantities
of carbonic acid as compared with those indicated in the Specification
of my former Patent dated June 22nd 1872, the treatment by carbonic
acid being continued until the proper point of saturation is reached, as
shown by the test used, as herein-before set forth.
In witness whereof, I, the said Edward Milner, have hereunto
set my hand and seal, this Eighteenth day of May, in the year
of our Lord One thousand eight hundred and seventy-six.