IMPROVEMENTS IN THE MANUFACTURE OF WHITE LEAD AND APPARATUS EMPLOYED THEREIN
Year: 1876

page_text: LETTERS PATENT to John Cowdery Martin, of 5, Upper Hill Street, Richmond,
in the County of Surrey, for the Invention of "IMPROVEMENTS IN THE
MANUFACTURE OF WHITE LEAD AND APPARATUS EMPLOYED THEREIN."
"
Sealed the 28th April 1876, and dated the 20th January 1876
PROVISIONAL SPECIFICATION left by the said John Cowdery Martin at the
Office of the Commissioners of Patents, on the 20th January 1876.
JOHN COWDERY MARTIN, of 5, Upper Hill Street, Richmond, in the County of
Surrey. "IMPROVEMENTS IN THE MANUFACTURE OF WHITE LEAD AND APPARATUS
EMPLOYED THEREIN."
2
My Invention consists in precipitating by means of carbonic acid gas carbonate
or white lead in a non-crystaline condition by employing a saturated or nearly
saturated solution of a neutral salt of lead as the acetate dissolved in water
(instead of using the largely diluted solutions of basic salt of lead, as heretofore
recommended), a further quantity of oxide of lead added gradually being held in
mechanical suspension in the solution, and which, becoming dissolved on the
temperature being raised, produces a sufficiency of the basic salt to set up and
continue the necessary chemical reactions on the introduction of the carbonic acid,
or I dissolve the oxide necessary to maintain the density of the solution separately
and cause it to flow into the precipitating vessel. I also carry on the decomposition
in presence of metallic lead in a form that exposes the largest amount of surface
to the solution, by which the resulting carbonate is produced of a pure white
colour.
I have discovered that to precipitate white lead in a non-crystaline condition
from oxide of lead dissolved in acid diluted with water, forming a solution of
soluable salt of lead, entirely depends on the proportion the acid solvent bears to
the quantity of water in such solution. If the water is in too great excess, and
the acid deficient, a large amount of basic salt of lead will, as is well known, be
formed; in that case the precipitating carbonic acid combines with so much energy
as to produce a crystaline deposit, and this has been the chief cause why all
attempts to produce white lead by means of precipitation equal in quality to that
made by the old or Dutch process have hitherto failed. When, however, the acid
solvent is in a greater proportion to the water less basic salt is produced in the
solution, and the combination of the carbonic acid takes place with less energy in
ID 71

page_text: presence of the larger quantity of acid solvent of the lead oxide which it has to
displace before the carbonate of lead can be formed, and this is then precipitated in
a perfectly amorphous and non-crystaline condition.
The precipitation is carried on in a vessel placed at a suitable elevation until a
considerable quantity of carbonate is held in mechanical suspension by the action
of a revolving agitator, when the whole or part is run off into a second vessel, and
the carbonic acid passed through the solution in this until it shews an acid reaction,
when it is forced under a strainer placed in a separate vessel, and through which
the clear solution rises, leaving the white lead on the bottom which is constructed
to be readily detached. The clear solution passes to the precipitating vessel, and
the white lead is removed and washed in a series of vacuum boxes or strainers
placed one above another, and arranged to be readily elevated, the washing liquor
passing through each from the upper to the lower, thence to an evaporator to be
concentrated, and from this to the first precipitating vessel. The white lead is
afterwards dried and finished for the market in the usual manner.
SPECIFICATION in pursuance of the conditions of the said Letters Patent filed
by the said John Cowdery Martin in the Great Seal Patent Office on the
20th July 1876.
JOHN COWDERY MARTIN, of 5, Upper Hill Street, Richmond, in the County of
Surrey. "IMPROVEMENTS IN THE MANUFACTURE OF WHITE LEAD AND APPARATUS
EMPLOYED THEREIN.
My Invention consists in precipitating by means of carbonic acid gas carbonate
or white lead in a non-crystalline condition by employing a saturated or nearly
saturated solution of a neutral salt of lead as the acetate dissolved in water
(instead of using the largely diluted solutions of basic salt of lead, as heretofore
recommended), a further quantity of oxide of lead added gradually being held in
mechanical suspension in the solution, and which, becoming dissolved on the
temperature being raised, produces a sufficiency of the basic salt to set up and
continue the necessary chemical reactions on the introduction of the carbonic acid,
or I dissolve the oxide requisite to maintain the density of the solution separately
and cause it to flow into the precipitating vessel. I also carry on the decomposition
in the presence of metallic lead in a form that will expose the largest amount of
surface to the solution, by which the resulting carbonate is produced of a fine
white colour.
I have discovered that to precipitate white lead in a non-crystalline condition
from oxide of lead dissolved in acid diluted with water forming a solution of
soluble salt of lead entirely depends on the proportion the acid solvent bears to
the quantity of water in such solution. If the water is in too great excess, and
the acid deficient, a large amount of basic salt will, as is well known, be formed.
In that case the precipitating carbonic acid combines with so much energy as to
produce a crystalline deposit, and this has been the chief cause why all attempts to
produce white lead by means of precipitation equal in quality to that made by the
old or Dutch process has hitherto failed. When, however, the acid solvent is in a
greater proportion to the water less basic salt is produced in the solution, and the
combination of the carbonic acid takes place with less energy in presence of the
larger quantity of acid solvent of the lead oxide which it has to displace before
the carbonate of lead can be formed, and this is then precipitated in a perfectly
amorphous and non-crystalline condition.
The precipitation is carried on in a vessel placed at a suitable elevation until a
considerable quantity of carbonate is held in mechanical suspension by the action
of a revolving agitator, when the whole or part is run off into a second vessel and
the carbonic acid passed through the solution in this until it shews an acid reaction,
when it is forced under a strainer placed in a separate vessel, and through which

page_text: the clear solution rises, leaving the white lead on the bottom which is constructed
to be readily detached. The clear solution passes to the precipitating vessel, and
the white lead is removed and washed in a series of vacuum boxes or strainers
placed one above another, and arranged to be readily elevated, the washing liquid
passing through each from the upper to the lower, thence to an evaporator to be
concentrated, and from this to the first precipitating vessel. The white lead is
afterwards dried and finished for the market in the usual manner.
In carrying out my Invention I make a solution of the neutral acetate or
crystalized sugar of lead in water, in which the weight of water is about one and
a-half times or less that of the crystalized acetate; or I make the solution with
the equivalent quantities of acetic acid, lead oxide, and water, and in a vessel by
preference of a circular form, fitted with a revolving agitator, I place, say 3600
gallons of this solution, temperature being about 60° Fahrenheit, and I suspend or
place in the vessel from 4 to 6 tons more or less of metallic lead in any form that
will cause the exposure of the largest amount of surface, or I granulate or reduce
to small pieces the whole or part of the lead and agitate it with suitable projections
fitted to the agitator. I then add about half a ton or less of oxide of lead, by
preference litharge, passing a current of carbonic acid gas through the solution
until the oxide has become converted into carbonate of lead of a sufficient white
colour, which if the flow of gas and the agitation has been sufficient will occur in
about an hour, more or less. I then add an additional half ton of litharge,
continuing as before, and if the lead oxide does not readily dissolve I gradually
raise the temperature to 90° or 100° Fahrenheit.
When the contents of the vessel have again become of a sufficiently white colour
I add a further quantity of about a ton of litharge, and if the conditions of the
decomposition and conversion have been well observed this quantity may be added
during each hour until as much has been converted as the vessel will contain.
Instead of adding the successive quantities of litharge to the solution as described
the said litharge may be passed into the solution in a regulated continuous stream
throughout the same time.
When the requisite condition of the white lead is obtained I pass the solution
containing it through a filtering press or through any suitable filtering material or
apparatus capable of separating the white lead from such solution, or having run
off the solution I allow the white lead to subside and return the clear solution to
the decomposing or converting vessel first described for re-use as before. The white
lead having been freed from as much of the solution as can be conveniently
separated is washed in as little water as possible. I effect this by placing two,
three, or more quantities of the white lead in separate vessels or apparatus, and
the water used for washing one is used upon the others in succession, and as the
operation proceeds and the quantities are changed fresh water is applied to the
quantity most washed and afterwards to the others, and finally to a quantity of
unwashed material, a process well understood in other manufactures.
The operation may be conducted in boxes having a suitable filtering material
placed a short distance from the bottom, and under which a partial vacuum can be
produced, or vats allowing the several washing waters to settle and be run off may
be used, or it may be conducted in any other convenient manner.
If at any stage of the washing operation a portion of the white lead from its
finely divided condition passes the filtering material or will not readily subside, I
pass a current of carbonic acid gas through the water or add to it a small quantity
of soda crystals (carbonate of soda) in solution.
I do not confine myself to the manner of procedure above described when using
the saturated or nearly saturated solution, nor to the precise quantity of litharge
or other oxide of lead to be acted upon by a given quantity of this solution at one
time, nor to passing a current of carbonic acid through the solution, as I sometimes
take a quantity of litharge, with which is combined from one-fourth to one-half of
its weight more or less of metallic lead granulated or in small pieces to admit of
being conveniently agitated, and add to it only so much of the solution as will

page_text: maintain it in a soft pasty condition, and I place this in a trough or in any
convenient vessel or apparatus where it can be readily agitated, and surround it
with an atmosphere of carbonic acid gas. At the end of about 48 hours the
litharge and a portion of the metallic lead will have become converted into white
lead of a very pure colour.
I further do not confine myself to any precise method of generating the carbonic
acid gas, but when passing this through the solution I prefer to generate it by the
combustion of coke or charcoal with chalk or limestone, passing the gas through
suitable purifiers previous to use. When the litharge or other suitable lead oxide
is added along with metallic lead, as before stated, to the solution in quantities
sufficient for the resulting white lead to form a paste I use carbonic acid generated
as above described, or by the decomposition of refuse tan or other materials which
will spontaneously produce it. evaporate the washing water in any suitable
apparatus, and when it has acquired the same specific gravity as the original
solution I return it to the precipitating vessel above described, or otherwise use it
to convert the litharge or other lead oxide as described.
I prefer to use an acetate of lead, as described, but a nearly saturated solution of
the nitrate may be used; I also use a chloride of lead formed or decomposed with
carbonic acid in the presence of metallic lead.
By a saturated or nearly saturated solution of a neutral salt of lead I would be
understood to mean when using the acetate (which I prefer) that the proportion of
water should be about one and a-half times the weight of the crystallized acetate
at a temperature of 60° Fahrenheit or thereabout, and in no case must the quantity
of water he greater than that which is found by experiment to produce a non-
crystalline precipitate and a given quantity of water must contain so much acetic
acid as would be sufficient to produce these proportions with the requisite amount
of lead oxide dissolved in the solution, and I would observe that the proportion
the water bears to the acetic acid, and consequently to the neutral acetate, is n
principal feature of my Invention, as determining the amount of basic salt of lead
present in the solution at any one time, and therefore (as I have found) of the
crystalline or non-crystalline character of the white lead produced. If the
temperature of the solution is raised above 100° Fahrenheit it should contain more
acid or neutral salt. When the neutral nitrate of lead is used instead of the
acetate the solution should likewise, for the reasons above given, be made with but
little more water than will hold that salt in solution at a given temperature.
I find that one of the causes of the inferiority of white lend as it has hitherto
been directed to be made from litharge or other similar lead oxide to that made
from metallic lead in the stacks appears to be due to the absence or deficiency of
the grey sub-oxide which the presence of metallic lead, as herein-before described,
supplies, and this mixing and becoming converted with the litharge or ready
formed oxide into white lead corrects the tendency lead oxides formed at high
temperatures have to produce a yellowish shade of colour when converted into the
commercial carbonate or white lead, and the conversion of these oxides combined
with metallic lead may be made to correct the low shade of grey white colour
present in the white lead produced from some varieties of metallic lead when
used alone.
I am aware that metallic lead has been directed to be used as a lining or
covering to certain apparatus where litharge was to have been converted into
white lead. This method of applying metallic lead is practically of little or no
effect in supplying the requisite quantity of sub-oxide to the lead oxide under
conversion, and does not appear to have been used in practise.
Having now described the nature of my said Invention, and the manner in
which the same is to or may be performed, I would have it understood that what I
claim as my Invention is,-
Firstly. The manufacture of white lead by the decomposition of a solution of the
acetate or nitrate of lead by means of carbonic acid gas in the presence of metallic
lead, and of a previously formed lead oxide, both being mixed with or contained

page_text: in such solution, as and for the purposes set forth, and whether the mixture forms
a fluid or is in a more or less semi-fluid condition.
Secondly. The manufacture of white lead by the decomposition of a saturated or
nearly saturated solution, as described, of the acetate or nitrate of lead by means
of carbonic acid gas, such decomposition taking place in the presence of either
metallic lead or of a previously formed lead oxide, or of both mixed with or
contained in such solution combined or not with the recovery by evaporation of
the solution containing the soluble salts of lead for re-use or otherwise.
Thirdly. The formation of a chloride of lead from litharge or other suitable lead
oxide in the presence of metallic lead, as described.
Fourthly. The conversion of chloride of lead into carbonate of lead by means
of carbonic acid gas in the presence of metallic lead, as described.
In witness whereof, I, the said John Cowdery Martin, have hereunto set my
hand and seal, this Nineteenth day of July, in the year of our Lord One
thousand eight hundred and seventy-six.
J. C. MARTIN. (L.S.)