Improvements in the Manufacture of White Lead.
Year: 1893

page_text: Date of Application, 26th Oct., 1893
Complete Specification Left, 27th Aug., 1894-Accepted, 29th Sept., 1894
PROVISIONAL SPECIFICATION.
Improvements in the Manufacture of White Lead.
We, JOHN HENRY NOAD, of 14 Stafford Road, East Ham, in the County of
Essex, Chemist and Electrician, and SEBASTIAN ZIANI DE FERRANTI, of
27 Charterhouse Square, in the County of London, Electrician, do hereby declare
the nature of this invention to be as follows:-
According to this invention we prepare acetate of ammonia in the same way as
described in our Specification 600992 but being slightly alkaline. We pour this
solution upon litharge which is contained in a closed still to which heat can be
applied. If the liquor is kept at boiling point the acetic acid at once attacks
the litharge, the ammonia liberated is distilled from the still, the gases, viz.-
steam and ammonia, are then passed through a cooling worm when they condense
and are stored in a suitable receptacle.
-
During this process the acetic acid only attacks the lead oxide (Pb. O.) present
in the litharge. All impurities are unacted upon and can afterwards be reduced,
when they have accumulated in sufficient quantity to the lower oxide of lead if the
impurity is in the form of a higher oxide of lead. Any metals that may be mixed
with the litharge are unacted upon as long as there is an excess of metallic lead
present, care being taken to keep this always present.
It is convenient to economise the amount of heat required for this part of the
process by the use of a vacuum.
The ammonia so obtained is then carbonated in the following manner-it is
pumped to the top of a tower or series of towers made of earthenware or other
suitable substance; which are filled with coke or pumice stone, and on descending
is met with a stream of gas containing carbonic acid gas (CO2). The gas on
leaving the first tower ascends to the second through which the ammonia liquor is
circulated, and on leaving this second tower ascends the third tower through which
water or acidulated water passes to catch any ammonia or ammonium carbonate
The gas used may be
which may have been blown over from the other towers.
drawn direct from the flue of a boiler, care being taken to pass the same through a
scrubber or washing tower so as to cool and remove any impurities. If this part of
the process has to be carried out quickly the gases may be obtained from a lime
kiln or other source in which the percentage of carbon dioxide (CO2) evolved is
greater than the first source.
The lead liquor which is still at boiling point is then drawn from the still through
filters into a closed mixing chamber made of wood or other suitable material.
This chamber has baffle pieces placed in the bottom and at the sides, and the
liquor is kept in constant agitation by means of an agitator revolving, so as to
continually change the surface of the liquor. In the side or top of this closed
chamber is inserted a nozzle or sprinkler through which the carbonated ammonia
The consequence
liquor previously filtered is injected in a fine spray or mist.
is that as the spray falls each particle of carbonated ammonia comes into contact
with fresh lead liquor. By this means we ensure the precipitation of a basic
carbonate of lead of uniform quality.
The liquor is then withdrawn through filter presses, extracting the white lead,
the resulting liquor, acetate of ammonia, being used to treat a fresh lot of
litharge.
We may also use the following process:-
We produce a neutral solution of acetate of lead by dissolving litharge in acetic
ian with further quantity of litharge to form a
.
C

page_text: basic acetate. We then take ammonium carbonate, which may be obtained by
carbonating ammonia as set out before, and having made the usual tests for lead
and the amount of carbon dioxide (CO2) required, we mix the amnionium carbonate
with the hot acetate of lead liquor as aforesaid, thus producing basic carbonate of
lead. The liquor is then pumped through a filter press before described, the
remaining liquor being ammonium acetate. This ammonium acetate is then put
into a still, and chalk or lime added. The whole is distilled and we get as distillate
ammonium carbonate, if chalk is used which is ready to renew the process or caustic
ammonia if lime, when this requires carbonating as aforesaid to continue the
process. We have also left in the still a solution of acetate of lime. To recover
the acetic acid we now add sulphuric acid which carries the lime down as sulphate
of lime, leaving acetic acid, which is ready to dissolve a further quantity of litharge
so as to continue the process.
We sometimes obtain acetate of lead by electrolysis, employing for this purpose
an apparatus consisting of a series of rectangular wooden vats or vessels in each of
which are contained nine or other convenient number of three sided wooden
frames; the frames are arranged side by side within the vat with diaphragms of
parchment paper or the like between frame and frame; wedges are inserted to
tighten the frames together. In this way a number of cells are formed, they are
open at the top. The frames are strengthened by cross bars, which also serve to
support leaden plates, one in each cell, at a distance from the cell walls. The
frames do not descend to the bottom of the vat and with the space beneath the
cells every alternate cell communicates by perforations in the bottom bar of
the frame.
The vat is to be charged with acetate of ammonia solution; this is introduced
into the cells at the top. A pipe is provided for drawing off the liquor from the
bottom compartment of the vat and the cells connected therewith. For emptying
the remaining cells a siphon is provided to each. The leaden plates are electrically
connected in two groups-those in the cell which communicate with the bottom
compartment forming one group and the remaining plates the other group. These
vats are connected electrically in series to any desired number and the circuit
includes a dynamo or source of electricity. In making the electrical connections
the emptying pipes may be utilised.
In some cases we carry on the process of mixing the solutions of lead and
carbonated alkali in a closed vessel so as to be able to employ a high temperature
and we may heat up not only the lead solution but also the ammonia solution
before the mixing takes place.
When the ammonia solution is hot and requires carbonating we may perform the
process of carbonating in closed vessels under pressure so as to get a sufficient
amount of carbonic acid taken up by the ammonia solution.
Dated this 25th day of October 1893.
JOHN H. NOAD.
S. Z. DE FERRANTI.
COMPLETE SPECIFICATION.
Improvements in the Manufacture of White Lead.
We, JOHN HENRY NOAD, of 14 Stafford Road, East Ham, in the County of
Essex, Chemist and Electrician, and SEBASTIAN ZIANI DE FERRANTI, of
27 Charterhouse Square, in the County of London, Electrician, 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 :-
According to this invention we prepare acetate of ammonia in the same way as
described in our Specification 600992 but being slightly alkaline. A suitable
solution is obtained by adding ammonia of sp. gr. 880 to acetic acid containing

page_text: 8 parts of glacial acid to 90 parts of water. We pour this solution upon litharge
which is contained in a closed still to which heat can be applied by a steam heated
coil or otherwise. The still is represented at a in the annexed drawing Figure 1.
The liquor is kept at boiling point and the acetic acid at once attacks the litharge,
the ammonia liberated is distilled from the still, the gases, viz.-steam and ammonia,
are then passed through a cooling worm contained in a tub when they condense
and are stored in a suitable receptacle c.
During this process the acetic acid only attacks the lead oxide (Pb. O.) present
in the litharge. All impurities are unacted upon and can afterwards be reduced,
when they have accumulated in sufficient quantity to the lower oxide of lead if
the impurity is in the form of a higher oxide of lead. Any metals that may be
mixed with the litharge are unacted upon as long as there is an excess of metallic
lead present, care being taken to keep this always present.
It may be convenient to economise the amount of heat required for this part of
the process by the use of a vacuum; if this be desired an air pump is applied in
a well known manner, but this pump is not indicated in the drawing.
The ammonia so obtained is then carbonated in the following manner:-It is
pumped from the receptacle c to the top of a tower or series of towers d d made of
earthenware or other suitable substance; which are filled with coke or pumice
stone, and on descending is met with a stream of gas containing carbonic acid
gas (CO2). The gas derived from any suitable source is forced through the towers
by a fan e and on leaving the first tower passes to the second, through both of
which the ammonia liquor is circulated, and on leaving this second tower the gas
ascends the third tower through which water or acidulated water passes to catch
any ammonia or ammonium carbonate which may have been blown over from the
other towers. The gas used may be drawn direct from the flue of a boiler, care
being taken to pass the same through a scrubber or washing tower so as to cool
and remove any impurities. If this part of the process has to be carried out
quickly the gases may be obtained from a lime kiln or other source in which the
percentage of carbon dioxide (CO2) evolved is greater than the first source.
The circulation of the ammonia liquor through the carbonating towers is continued
until sufficient carbonic acid has been absorbed to precipitate the lead which has
been brought into solution in the still and the carbonising operation is then
stopped.
The lead liquor which is still at boiling point is drawn from the still through
filters into a receiving vessel g which may be provided with a heating coil to
restore the heat lost in the operation of filtering. When the whole of the charge
is through the filters it is passed on into a closed mixing chamber h made of wood
or other suitable material. This chamber has baffle pieces placed in the bottom
and at the sides, and the liquor is kept in constant agitation by means of an agitator
revolving, so as to continually change the surface of the liquor. The agitator is
an axis standing vertically in the mixing chamber and having arms carrying
paddles; the axis is rapidly driven and the baffle pieces serve to check the uniform
In the
rotary movement of the liquid which the agitator would otherwise set up.
side or top of this closed mixing chamber is inserted a nozzle or sprinkler or finely
perforated rose through which the carbonated ammonia liquor previously filtered
through the filter i is injected in a fine spray or mist. The consequence is that as
the spray falls each particle of carbonated ammonia comes into contact with fresh
lead liquor. By this means we ensure the precipitation of a basic carbonate of
lead of uniform quality.
When the whole of the charge of carbonated ammonia solution has been drawn
down into the mixing chamber and the precipitation is complete the liquor is
withdrawn by the pump; and forced through filter presses extracting the white
lead, the resulting liquor, acetate of ammonia, being passed into a tank a ready to
be used to treat a fresh lot of litharge. The white lead is removed in cakes from
the filter press; these are broken up and the material is washed and dried to
prepare it for the market.

page_text: We may also use the following process:-
We produce a neutral solution of acetate of lead by dissolving litharge in acetic
acid. This may be done without heat by allowing an eight per cent. acid to flow
over an extended surface of litharge. We then boil this solution with a further
quantity of litharge to form a basic acetate. We then take ammonium carbonate,
which may be obtained by carbonating ammonia as set out before, and having
made the usual tests for lead and provided the amount of carbon dioxide (CO2)
required to precipitate it, we mix the ammonium carbonate with the hot acetate
of lead liquor as aforesaid in a chamber such as h, thus producing basic carbonate
of lead. The liquor is then pumped through a filter press as before described,
the remaining liquor being ammonium acetate. This ammonium acetate is then
put into a still which replaces the still a and chalk or lime added. The whole
is distilled and we get as distillate ammonium carbonate, if chalk is used, which
is ready to renew the process or caustic ammonia, if lime, when this requires
carbonating as aforesaid to continue the process. We have also left in the still
a solution of acetate of lime. To recover the acetic acid we now add sulphuric
acid which carries the lime down as sulphate of lime, leaving acetic acid, which
is ready to dissolve a further quantity of litharge so as to continue the process.
We sometimes obtain acetate of lead by electrolysis, employing for this purpose
an apparatus consisting of a series of rectangular wooden vats or vessels in each of
which are contained nine or other convenient number of three sided wooden
frames; such an apparatus is represented by Figures 2 to 7 of the annexed
drawings. Figure 2 is a plan, Figure 3 is a longitudinal section and Figure 4 is
a transverse section. Figure 5 is an elevation of one of the frames. Figure 6 is a
plan and Figure 7 is a vertical section of the same. The frames are arranged
side by side within the vat m with diaphragms n of parchment paper or the like
between frame and frame; wedges o o are inserted to tighten the frames together.
In this way a number of cells are formed, they are open at the top. The frames
are strengthened by cross bars which also serve to support leaden plates pp
one in each cell at a distance from the cell walls. The frames do not descend to
the bottom of the vat and with the space beneath the cells every alternate cell
communicates by perforations 12 in the bottom bar of the frame.
The vat is to be charged with acetate of ammonia solution; this is introduced
into the cells at the top. A pipe q is provided for drawing off the liquor from the
bottom compartment of the vat and the cells connected therewith. For emptying
the remaining cells a siphon is provided to each. The leaden plates are
electrically connected in two groups-those in the cell which communicate with
the bottom compartment forming one group and the remaining plates the other
group. These vats are connected electrically in series to any desired number by
conductors indicated by dotted lines and the circuit includes a dynamo or source of
electricity. In making the electrical connections the emptying pipes may be
utilised.
When the electrolysis is sufficiently progressed the resulting ammoniacal and
lead solutions are drawn off separately and they are treated as already described
for the production of white lead.
In some cases we carry on the process of mixing the solutions of lead and
carbonated alkali in a closed vessel of sufficient strength to allow a working
pressure of say 50 lbs. to the inch to be maintained so as to be able to employ
a high temperature and we heat up the lead solution until such a pressure is
attained. We then inject the spray of the solution, carbonated ammonia.
We
may heat not only the lead solution but also the ammonia solution before the
mixing takes place.
Having now particularly described and ascertained the nature of our said
invention and in what manner the same is to be performed we declare that what
we claim is :-
1. The process substantially as described for manufacturing white lead consisting

page_text: in treating litharge with acetate of ammonia in solution (obtaining thereby
ammonia and acetate of lead in solution), then carbonating the ammonia and
using it to precipitate white lead from the acetate of lead solution.
2. In the manufacture of white lead by the precipitation of acetate of lead with
carbonated ammonia, the spraying or subdivision of the liquor so that each particle
of carbonated ammonia comes into contact with fresh lead liquor.
3. The process substantially as described, for manufacturing white lead, consisting
in dissolving litharge with acetic acid, then precipitating the basic acetate with
carbonated ammonia and afterwards recovering the ammonia and the acetic acid
from the residual liquor by the use of chalk or lime and sulphuric acid.
4. Electrolytic cells substantially as described to be used in the manufacture of
white lead; such cells containing frames supporting leaden plates and porous
diaphragms separating the liquids in which adjacent plates are immersed.
5. In the manufacture of white lead by the precipitation of acetate of lead with
carbonated ammonia, the use of a closed mixing vessel of sufficient strength and
maintaining a high temperature and pressure in the mixing vessel.
Dated this 27th day of August 1894.
JOHN H. NOAD.
S. Z. DE FERRANTI.