Improvements in the Manufacture of White Lead.
Year: 1892

page_text: Date of Application, 21st Dec., 1892
Complete Specification Left, 23rd Oct., 1893-Accepted, 21st Mar., 1894
PROVIDIUNAL DE
Improvements in the Manufacture of White Lead.
We, SEBASTIAN ZIANI DE FERRANTI, of Charterhouse Square in the City of
London, Electrician, and JOHN HENRY NOAD, of 10 Lichfield Terrace, East
Ham, in the County of Essex, Chemist, do hereby declare the nature of this invention
to be as follows:-
Our invention relates to the production of white lead from a soluble salt of lead
obtained by electrolysis and by the precipitation of the same with a carbonated
alkali.
The electrolizer we construct of a series of lead plates similar the one to the
other and cast with flanges around their edges. These plates are locked up
together in a frame as in a filter press. Between plate and plate there is in each
case a porous diaphragm it may be of parchment paper which is strengthened and
rendered insulating at the edges and lower part by vulcanised india rubber or
otherwise. Thus a series of cells are formed and these are filled with an alkaline
solution preferably a ten per cent. solution of acetate of ammonia. The plates are so
formed as to provide filling holes at the top of the cells and emptying holes at the
bottom. The terminal plates of the series are connected with a dynamo or other
source of constant current with the result that acetate of lead is formed on one
The outlets or emptying
side of each diaphragm and caustic ammonia on the other.
holes range in two lines beneath the bottoms of the cells; they are closed by
hinged metal flaps or valves, one for each series, and to render the flap watertight
and to preserve insulation the flap contains an india rubber bag containing water
under a pressure sufficient to hold the face of the bag firmly against the orifices to
be closed.
When the electrolysis is sufficiently advanced the flaps are opened and the liquid
is let down from the cells; the lead solution into one receiving tank and the
caustic ammonia into another.
The ammonia is pumped to the top of a carbonising tower and descends amongst
coke with which the tower is filled. In the tower the ammonia meets a current of
gas containing carbonic acid and it is circulated through and through the tower
until the proper degree of carbonization is obtained. The gas after leaving the
carbonising tower before it is allowed to escape is passed through another tower
where it is brought into contact with acid which stops any ammonia the gas may
carry off with it.
The tank containing the lead solution is heated by a steam coil and when at a
suitable temperature which has a considerable influence on the quality of the
products the liquid (which is filtered) is run together with the solution of
carbonated alkali (which also is filtered) into a mixing tank, care being taken to
Precipitation
maintain a suitable proportion between the lead and the carbonate.
ensues and afterwards the contents of the mixing vessel are pumped through a
filter press which retains the white lead whilst the solution passes on into a close
chamber in which it is submitted to distillation by being sprinkled over a steam
heated coil; this volatilises ammonia and any ammonium carbonate which may be
present and these pass to a condenser whilst the acetate of ammonia solution is run
into store vessels from which the electrolizer is supplied. The ammonia from the
condenser passes into the mixing chamber. In this way the presence of an excess
of ammonia in the mixing vessel is ensured over and above the carbonated
ammonia which passes through the electrolizer; this excess of ammonia has an

page_text: important influence on the quality of the product. A vacuum may be maintained
in the still if desired by means of a steam jet.
Dated this 20th day of December 1892.
S. Z. DE FERRANTI.
JOHN H. NOAD.
COMPLETE SPECIFICATION.
Improvements in the Manufacture of White Lead.
We, SEBASTIAN ZIANI DE FERRANTI, of Charterhouse Square, in the City of
London, Electrician, and JOHN HENRY NOAD, of 10 Lichfield Terrace, East
Ham, in the County of Essex, Chemist, 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 more especially to improvements on the process described
in the Specification of a former Patent granted to us No. 6009 in the year 1892.
In this process acetate of ammonia is decomposed by electrolysis with lead
electrodes. This operation yields a lead solution and caustic alkali which is
afterwards carbonated. On mixing the two solutions white lead is precipitated.
As the process was formerly conducted the whole of the lead could not
advantageously be precipitated by the carbonated alkali but a certain amount had
to be left in solution, to be afterwards removed by the addition of chromic acid.
The cost of production of white lead was thereby increased.
By our present invention we are able at once to precipitate the whole of the
lead in solution as white lead. We attain this end by heating the lead solution
and precipitating white lead from the hot solution; also by employing in the
mixing vessel an excess of ammonia over and above that which comes from
the electrolyser; this excess of ammonia we afterwards separate by distillation.
Our invention also relates to improvements in the electrolyser.
The electrolizer we construct of a series of lead plates similar the one to the
other and cast with flanges around their edges. These plates are locked up
together in a frame as in a filter press. Between plate and plate there is in each
case a porous diaphragm it may be of parchment paper which is strengthened and
rendered insulating at the edges and lower part by vulcanised india rubber or
otherwise. Thus a series of cells are formed and these are filled with an alkaline
solution preferably a ten per cent. solution of acetate of ammonia. The plates are
so formed as to provide filling holes at the top of the cells and emptying holes at
the bottom. The terminal plates of the series are connected with a dynamo or
other source of continuous current with the result that acetate of lead is formed on
one side of each diaphragm and caustic ammonia on the other. The outlets or
emptying holes range in two lines beneath the bottoms of the cells; they are
closed by hinged metal flaps or valves, one for each series, and to render the flap
watertight and to preserve insulation the flap contains an india rubber bag
containing water under a pressure sufficient to hold the face of the bag firmly
against the orifices to be closed.
When the electrolysis is sufficiently advanced the flaps are opened and the liquid
is let down from the cells; the lead solution into one receiving tank and the caustic
ammonia into another.
With this electrolyser we are able to work with less electro motive force than
heretofore ranging according to the density of the solution from 1 to 1-6 volts per
cell. This electrolyser is also easy to keep in working order as sludge cannot
accumulate. The emptying flaps also are easy of manipulation.
In order that our invention may be fully understood and readily carried into
effect we will proceed to describe the drawings hereunto annexed.

page_text: DESCRIPTION OF THE DRAWINGS.
Figure 1 shows the general plan of the plant we provide for the manufacture of
white lead.
Figure 2 is a plan partly in section and Figure 3 is a transverse section of the
electrolyser.
Figures 4 and 5 represent one of the diaphragms.
Figure 6 is a diagram to aid in the description of the diaphragm.
Referring to Figure 1 the routine of working may be traced as follows:-
Ammonia is pumped by pump P¹ from a tank to the top of carbonating towers T¹
and T' and it descends amongst coke with which the towers are filled. In the
towers the ammonia meets a current of gas containing carbonic acid (CO₂) drawn
from suitable source y by blower R and it is circulated through and through the
towers until the proper degree of carbonation is obtained, that is to say, until there
sufficient carbonic acid absorbed to precipitate the whole of the lead in the lead
solution with which the carbonated alkali is afterwards to be mixed. A slight
excess of carbonic acid is unobjectionable. The liquor from the towers T¹ T' is
filtered in filter F. The gas after leaving the carbonating tower before it is
allowed to escape is passed through another tower T' also filled with coke where
it is brought into contact with acid which stops any ammonia or ammonium
carbonate the gas may carry off with it.
The lead solution which is drawn from the electrolyser E after being filtered in
the filter F is run into a tank S₁ and heated to the boiling point by a steam coil
supplied from a suitable source x. This elevation of temperature has a considerable
influence on the quality of the products. The liquids, that is to say, the lead
solution and the carbonated alkali from the tanks S1 and S2 are run together in
fine showers into a mixing tank M. care being taken to maintain a suitable
proportion between the lead and the carbonate. Complete precipitation ensues and
afterwards the contents of the mixing vessel are pumped by the pump P³ through
a filter press F P which retains the white lead whilst the solution is passed on by
the pump P into a close chamber C' in which it is submitted to distillation by
being sprinkled over a steam heated coil supplied from a suitable source X or
otherwise. This volatilises ammonia and any ammonium carbonate which may be
present and these pass to a condensing coil C2 whilst the acetate of ammonia
solution is pumped by the pump P into the store vessel A from which the
electrolyser E is supplied. The ammonia from the condenser passes into the mixing
chamber M either directly or into S so as to pass through the carbonating tower.
In this way the presence of an excess of ammonia in the mixing vessel is ensured
over and above the ammonia which passes through the electrolyser; this excess of
ammonia has an important influence on the quality of the product and it is to be
constantly maintained when necessary by the importation into the process of
additional ammonium.
At every stage of the process care is taken to avoid loss of ammonia, the
reactions being carried on in closed vessels and any ammonia vapours which cannot
otherwise be retained are led into the acid tower.
Except as herein stated the manufacture should be conducted as described in the
Specification of our former Patent.
We will now describe the drawings Figures 2 to 6 which relate to the
electrolyser.
a is a base which by standards a' a' carries the two side bars or bearers a³ a²;
also at one end the abutment plate a³ and at the other the bearing for the locking
screw b.
ccc are a series of flanged plates of cast lead, they are all alike and
they have lugs c' which serve to support them, resting upon the insulating blocks d
of hard wood or other material which lie upon the bearers a². Between every
plate and the next a diaphragm e is placed. At one end of the series a sheet of
insulating material is interposed between the leaden plate and the abutment a³ to

page_text: prevent electrical conduction and to ensure a water tight joint. At the other end
of the series a similar sheet is interposed between the leaden plate and the
pressure plate g. The screw abuts on the plate g and by its pressure all the joints
are closed water tight. On each plate care two filling orifices and also two
sets of outlet passages c³c³. When at work the outlets are closed by the flaps h h
which are hinged to the frame at . Upon each flap and extending the whole
length of the apparatus there is a bag of india rubber or other suitable material ¿
and by a flexible pipe water is admitted to the bag under sufficient pressure to bring
the side of the bag against the outlets to close them and to keep them closed.
The apparatus can then be filled through the holes and in this operation care
must be taken not to bulge the diaphragms by inequality of pressure. The flaps /
rest at intervals on the blocks k k. When it is desired to empty the apparatus the
electrolysis having been carried sufficiently far the blocks k can be withdrawn and
the water pressure can be cut off from the bags i. The two liquors then descend
into separate receiving compartments I and m in the base and they pass away in
separate tanks by pipes provided for the purpose.
The electrical connectious may be made in any convenient manner, as by soldering
the conductors on to the terminal plates cc of the series.
The diaphragms we make preferably of stout Willesden paper; this material is
cut to the form shown by Figure 4 and along the lower edge of the diaphragm we
split the paper (which can be done without difficulty) and introduce a strip of sheet
india rubber o. Also around the edges of the diaphragm we stick strips of water-
proof fabric p p. The strips p p serve to make watertight joints when the plates
are locked up together. The india rubber strips o serve to prevent electrolysis
taking place at the lower part of the cells, for it is found that here for a depth of
an inch or so, the lead solution tends to be of considerably higher density than in
the upper part of the cell which but for the precaution described would cause
irregularity in the action.
Having now particularly described and ascertained the nature of our said inven-
tion and in what manner the same is to be performed, we declare that what we
claim is:
1. In the process of the manufacture of white lead by electrolysis and
precipitation the means substantially as described for obtaining the precipitation
as white lead of the whole of the lead which has passed into solution: such means
consisting in heating the liquor and adding alkali over and above that which results
from electrolysis simultaneously with the formation of the lead solution.
2. In the process of the manufacture of white lead by electrolysis and
precipitation subjecting the liquor after precipitation and before returning it to
the electrolyser to a process of distillation whereby ammonia is separated from it
and the liquor is rendered more suitable for use in the electrolyser.
3. An electrolyser substantially as described having flanged plates with
diaphragms between, locked together in a frame to form cells.
4. In an electrolyser substantially as described, having a series of cells with exit
openings at the bottom, elastic bags distended by fluid within and thereby caused
to close such openings.
5. In an electrolyser substantially as described having diaphragms of porous
material nipped and held between flanged plates the means for preventing
electrolysis in the lower part of the sill by inserting nonconducting material into
the lower part of the diaphragm.
Dated this 23rd day of October 1902
'CARPMAEL & Co.,
Agents for the Applicants.