Improvements in the Production of White Lead and Chrome Pigments.
Year: 1892

page_text: Date of Application, 28th Mar., 1892
Complete Specification Left, 24th Dec., 1892-Accepted, 28th Jan., 1893
PROVISIONAL SPECIFICATION.
Improvements in the Production of White Lead and Chrome
Pigments.
We, SEBASTIAN ZIANI DE FERRANTI, of 120 Fellows Road, Hampstead, in
the County of Middlesex, 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:-
:-
According to this invention we first obtain by electrolysis from anodes of crude
lead in a salt of one of the alkalies a soluble salt of lead and a solution of the
alkali, we then carbonate the alkaline solution and afterwards add such solution to
the solution of the salt of lead-thereby producing white lead and a solution of
the alkaline salt, still containing a small proportion of the soluble salt of lead and
which when purified from the remaining soluble salt of lead can be again used in
the electrolytic bath. Preferably to purify the solution of the alkaline salt by
the addition to it of chromic acid to separate the lead as chromes.
The process may be conducted as follows:-
PREPARATION OF SOLUBLE SALT OF LEAD.
1. We prepare acetate of lead from lead electrodes immersed in acetate of
ammonia, we prefer to use 10% solution which may be prepared by taking 90 parts
of water 8 of glacial acetic acid by weight and then making the solution neutral
by addition of sufficient quantity of 880 ammonia solution. Suitable tanks made of
earthenware, slate, wood lined with lead, or wood lined with pitch or alphalte are
taken, and a number of porous pots, or frames, covered with porous diaphragms so
as to form porous pots or porous slabs mounted so as to form partitions, are
immersed in the bath. The solution is poured into the porous pots and bath so as
to get an equal level.
Electrodes are then immersed one in each porous pot, and one on either side of
The electrodes are grooved corrugated or otherwise so constructed as to
present the most surface in the smallest space.
same.
A convenient number of sets of tanks are connected in series in proportion to
the voltage say in such a manner as to provide about 2 volts for each cell. The
positive pole of the source of current, either dynamo or battery, is connected to
the outer sets of electrodes in the first tank, the electrodes in porous cells in first
tank are connected to the outer electrode in the second and so on.
On passing a direct current through these cells acetate of lead is formed in the
outer solution and ammonia set free in the porous cell. This is absorbed by the
water. The gas can be prevented clinging to the plates in the porous cells by means
The process is
of agitation. If desirable gas can be collected in a suitable receiver.
continued until the ammonia solution is sufficiently saturated say to about 4th of
complete saturation which can be told by analysis or inspection of the index of a
registering electric meter.
As soon as the desired degree of saturation is reached the liquor in the outer of
cach tank can be run into another tank through a filter press and the liquor in cach
porous cell can also be run into another tank and the first tank and the porous
cells in same can be refilled with acetate of ammonia, and the process can thus be
carried out continuously; contacts being provided so to cut any one tank of a series
out of circuit for re-filling and cleaning purposes.
The ammonia solution is now run into 3 or more carbonating vessels which.arc
about filled with the liquor. Each of these vessels has a coil of lead pipe in the
bottom, the coil being perforated with a number of small holes. Gas contain-
ing CO₂, or pure CO₂ from a suitable source is then taken through a pipe connected
:

page_text: with the perforated coil in base of 1st carbonating vessel. The CO, gas then acts
directly on the ammonia, carbonating it and any excess of gas is conducted from
the top of the vessel by another lead pipe leading to the lead coil at the bottom of
the 2nd vessel. From the 2nd vessel CO, gas is lead to the third, and from third
vessel it is led to a fourth which may take the form of scrubber or tower down
which dilute H,SO, flows. The result is that the ammonia in the first vessel is
carbonated to desired degree, which is determined by an analysis of a small
quantity withdrawn during operation, the second catches any of the carbonate of
ammonia which may escape from the first the third is not quite so much carbonated
and catches any carbonated ammonia which may come from the first and second
vessels. The fourth vessel catches any ammonia escaping with waste gas, which is
thus saved.
1. The time when the ammonia liquor has become sufficiently carbonated may be
determined in the following manner:
The whole quantity of lead which has been dissolved being known either from
the readings of an electric current meter, or by an analysis of a measured sample of
the lead solution.
The quantity of carbonic acid necessary to convert this lead into whitelead is
easily calculated from the known composition of the best samples of white lead
(80 parts of lead by weight require 11.3 parts by weight of carbonic acid (CO2)*
for their conversion). Samples of measured volume are withdrawn from time to
time from the carbonates, an equal quantity of liquid being taken from each
carbonating vessel and these being mixed to form a sample of the average
composition of the liquid in the carbonators.
The weight of carbonic acid in this average sample is determined by analysis
and hence the whole weight of carbonic acid absorbed in the carbonators is found;
the blowing in of carbonic acid is continued till the weight thus found is nearly but
not quite equal to the weight necessary to convert the dissolved lead into white lead.
(2) A qualitative test may be made by mixing portions of the lead solution and
the solution from the carbonators in the same proportion, as the whole volumes of
the liquors from which they are taken bear to each other.
The nature, quantity, and rate of settling of the precipitate is observed and the
amount of excess of lead in the filtrate estimated by precipitation with chromic
acid or otherwise.
When the ammonia liquor has been sufficiently carbonated it should be pumped
through a filter press in order in order to rid it of all solid impurities and allowed
to mix in a tank with the acetate of lead solution which has also been passed-
through a filter press in order to rid it also from solid impurities. The result.
being that a white precipitate is at once formed consisting of an hydrated carbonate
of lead in such a proportion as to form what is commercially known as white lead.
The contents of the tank are then pumped through a suitable filter press in which
it leaves behind the whole of the precipitate in the form of cakes, which must be
washed free of liquor and then dried, the resulting liquor being chiefly acetate of
ammonia containing a small percentage of acetate of lead. The whole of this
liquor' is passed into another settling tank, when it has sufficient commercial chromic
acid added to it to precipitate the whole of the lead in the form of chromes, the
color of which can be controlled (1) by the solution at the time of precipitation
being more or less alkaline (2) by allowing liquor containing a small percentage
of free acetate of lead to remain in contact with the precipitated chrome. Under
these circumstances the first formed chromes will take up more lead, the result
being a darker color.
.
The liquor and precipitate from these tanks is passed through a filter press, as
before described in the case of white lead, the resulting liquor being simply acetate
of ammonia, which is returned to the acetate of ammonia tank.
With regard to the treatment of the ammonia with CO₂, this can be accomplished
in' the following manners :-
1. Supposing the plant be one in which there is a steam engine used, a Roots

page_text: blower or blowing engine can be used to draw the flue gases straight from the
fines of the furnace, these gases can be passed through cylinders, vessels or
scrubbers some containing ferric oxide to remove sulphur compounds, and the others
wet coke to cleanse and cool the gas. This arrangement removes the solid
impurities and sulphides, the resulting gas is then led through the vessels as
described above, the CO, carbonating the ammonia, and the nitrogen and other
accompanying gases passing through without affecting the ammonia.
2. A kiln may be used in which chalk or limestone is burnt with a certain
amount of coal, the resulting gases being led through the same purifying
arrangement above described.
In this case the production of CO, is accompanied by the production of a large
quantity of lime.
The white lead produced by this process compares in density color and covering
power with the finest lead produced by the Dutch process.
In place of using acetate of ammonia other alkaline acetates or other alkaline
salts might be used. For example
1. Acetate of soda, or acetate of potash can be used; caustic soda (NaOH) or
caustic potash (KOH) being set free in the inner cell instead of ammonia. The
caustic soda or potash liquor is then carbonated, the process being in all respects
similar to that in which acetate of ammonia is used-but the precipitated whitelead
is not so easily washed free from the soluble salts of potash and soda as it is from
ammonia salts.
2. Nitrate solutions can be used, nitrate of lead being formed and alkali being set
free in the porous vessel containing the cathode, but in using these solutions it is
necessary to employ a cathode containing oxides of metals; as litharge or copper
oxide (CO) to combine with the hydrogen otherwise the nascent hydrogen
reduces the nitrates in the inner cell to ammonia and thus partially spoils the
regenerative nature of the process.
For example to electrolise a nitrate of potash solution we can employ a copper
oxide electrode in the porous cell the copper oxide being reduced during the process
to metallic copper, which is reoxidised by subsequent heating in an air current is
then ready to be used again. The E.M.F. of polarization is reduced by about
0.6 volts by the employment of a copper oxide cathode.
Dated this 28th day of March 1892.
CARPMAEL & Co.,
Agents for the Applicants.
COMPLETE SPECIFICATION.
Improvements in the Production of White Lead and Chrome
Pigments.
We, SEBASTIAN ZIANI DE FERRANTI, of 120 Fellows Road, Hampstead in
the County of Middlesex, 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 :-
According to this invention we first obtain by electrolysis from anodes of crude
lead in a salt of one of the alkalies a soluble salt of lead and a solution of the
alkali, we then carbonate the alkaline solution and afterwards add such solution to
the solution of the salt of lead-thereby producing white lead and a solution of the
alkaline salt still containing a small proportion of the soluble salt of lead, and
which when purified from the remaining soluble salt of lead, can be again used in
the electrolytic bath. Preferably we purify the solution of the alkaline salt by
the addition to it of chromic acid to separate the lead as chromes.
The process may be conducted as follows:-
We prepare acetate of lead from lead electrodes immersed in acetate of ammonia,

page_text: we prefer to use a 10% solution which may be prepared by taking 90 parts of
water 8 of glacial acetic acid by weight and then making the solution neutral by
addition of sufficient quantity of 880 ammonia solution. Suitable tanks made of
earthenware, slate or wood lined with lead or wood lined with pitch or asphalte are
taken, and a number of porous pots (or frames covered with porous diaphragms so
as to form porous pots) or porous slabs mounted so as to form partitions, are
immersed in the tauk. The solution is poured into the porous pots and tank so as
to get an equal level.
Electrodes are then immersed one in each porous pot, and one on either side of
same. The electrodes are grooved corrugated or otherwise so constructed as to
present the most surface in the smallest space.
A convenient number of tanks thus mounted are connected in series in proportion
to the voltage-say in such a manner as to provide about 2 volts for each tank.
The positive pole of the source of current, either dynamo or battery, is connected
to the outer sets of electrodes in the first tank, the electrodes in the porous cells in
first tank, are connected to the outer electrodes in the second and so on.
ידי
On passing a direct current through these cells acetate of lead is formed in the
outer solution and ammonia set free in the porous cell. This is absorbed by the
water. The hydrogen gas generated can be prevented clinging to the plates in
the porous cells by means of agitation. If desirable the gas can be collected in a
suitable receiver. The process is continued until the ammonia solution is sufficiently
saturated say to about th of complete saturation which can be told by analysis or
inspection of the index of a registering electric meter.
As soon as the desired degree of saturation is reached the liquor in the outer of
each tank can be run into another tank through a filter press and the liquor in each
porous cell can also be run into another tank and the first tank and the porous cells
in same can be refilled with acetate of ammonia, and the process can thus be carried
out continuously; contacts being provided so as to cut any one tank of a series out
.of circuit for refilling and cleaning purposes.
The ammonia solution is now run into 3 or more carbonating vessels which are
about filled with the liquor. Each of these vessels has a coil of lead pipe in the
bottom, the coil being perforated with a number of small holes. Gas containing
carbonic acid, or pure carbonic acid from a suitable source is then taken through a
pipe connected with the perforated coil in base of 1st carbonating vessel. The
carbonic acid gas then acts directly on the ammonia, carbonating it and any excess of
gas is conducted from the top of the vessel by another lead pipe leading to the
lead coil at the bottom of the 2nd vessel. From the 2nd vessel carbonic acid gas
is led to the third, and from third vessel it is led to a fourth which may take, the
form of scrubber or tower down which dilute sulphuric acid flows. The result is
that the ammonia in the first vessel is carbonated to the desired degree, which is
determined by an analysis of a small quantity withdrawn during operation, the
second catches any of the carbonate of ammonia which may escape from the first
the third is not quite so much carbonated and catches any carbonated ammonia
which may come from the first and second vessels. The fourth vessel catches any
ammonia escaping with waste gas, which is thus saved.
The time when the ammonia liquor has become sufficiently carbonated may be
determined in the following manner:
(1) The whole quantity of lead which has been dissolved being known (either
from the readings of an electric current meter, or by an analysis of a measured
sample of the lead of solution) the quantity of carbonic acid necessary to convert
this lead into white lead is easily calculated from the known composition of the best
samples of white lead (80 parts of lead by weight require 11.3 parts by weight of
carbonic acid (CO) for their conversion). Samples of measured volume are with-
drawn from time to time from the carbonators, an equal quantity of liquid being
taken from each carbonating vessel and these being mixed to form a sample of the
average composition of the liquid in the carbonators.
The weight of carbonic acid in this average sample is determined by analysis

page_text: and hence the whole weight of carbonic acid absorbed in the carbonators is found;
the blowing in of carbonic acid is continued till the weight thus found is nearly but
not quite equal to the weight necessary to convert the dissolved lead into white
lead.
The liquid when thus carbonated should still contain a considerable excess of
caustic ammonia.
(2) A qualitative test may be made by mixing portions of the lead solution and
the solution from the carbonators in the same proportion, as the whole volumes of
the liquors from which they are taken bear to each other.
The nature quantity and rate of settling of the precipitate is observed, and the
amount of excess of lead in the filtrate estimated by precipitation with chromic
acid or otherwise.
When the ammonia liquor has been sufficiently carbonated, it should be pumped
through a filter press in order to rid it of all solid impurities and allowed to mix in
a tank with the acetate of lead solution which has also been passed through a filter
press in order to rid it also from solid impurities. The result being that a white
precipitate is at once formed consisting of an hydrated carbonate of lead in such a
proportion as to form what is commercially known as white lead.
The contents of the tank are then pumped through a suitable filter press in
which it leaves behind the whole of the precipitate in the form of cakes, which
must be washed free of liquor and then dried.
The liquor from which the precipitate is separated is chiefly acetate of ammonia
and contains also a small percentage of acetate of lead.
The whole of this liquor
is passed into another settling tank, when it has sufficient commercial chromic acid
added to it to precipitate the whole of the lead in the form of chromes. Preferably
the process is so worked that about 5 per cent. of the lead passing into solution is
ultimately converted into chrome. The colour of the chrome can be controlled
(1) by the solution at the time of precipitation being more or less alkaline, (2) by
allowing liquor containing a small percentage of free acetate of lead to remain in
contact with the precipitated chrome. Under these circumstances the first formed
chromes, will take up more lead, the result being a darker color.
The liquor and precipitate from these tanks is passed through a filter press, as
before described in the case of white lead, the resulting liquor being simply acetate
of ammonia, which is returned to the acetate of ammonia tank.
With regard to the treatment of the ammonia with carbonic acid, this can be
accomplished in the following manners:-
1. Supposing the plant be one in which there is a steam engine used, a Roots
blower or blowing engine can be used to draw the flue gases straight from the flues
of the furnace, these gases can he passed through cylinders vessels or scrubbers
some containing ferric oxide to remove sulphur compounds, and the others wet
coke to cleanse and cool the gas. This arrangement removes the solid impurities
and sulphides, the resulting gas is then led through the vessels as described above,
the carbonic acid carbonating the ammonia, and the nitrogen and other accom-
panying gases passing through without affecting the ammonia.
2. A kiln may be used in which chalk or limestone is burnt with a certain
amount of coal, the resulting gases being led through the same purifying arrange-
ment above described.
In this case the production of carbonic acid is accompanied by the production of
a large quantity of lime.
The white lead produced by this process compares in density color and covering
power with the finest lead produced by the Dutch process.
In place of using acetate of ammonia, other alkaline acetates or other alkaline
salts might be used. For example:-
1. Acetate of soda or acetate of potash can be used; caustic soda, (NaOH) or
caustic potash (KOH) being set free in the inner cell instead of ammonia. The
caustic soda or potash liquor is then carbonated, the process being in all respects
similar to that in which acetate of ammonia is used, but the precipitated whitelead

page_text: is not so easily washed free from the soluble salts of potash and soda as it is from
ammonia salts.
2. Nitrate solutions can be used, nitrate of lead being formed and alkali being
set free in the porous vessel containing the cathode, but in using these solutions it.
is necessary to employ a cathode containing oxides of metals; as litharge or copper
oxide (CuO) to combine with the hydrogen, otherwise the nascent hydrogen
reduces the nitrates in the inner cell to ammonia, and thus partially spoils the
regenerative nature of the process.
For example to electrolise a nitrate of potash solution, we can employ a copper
oxide electrode in the porous cell, the copper oxide being reduced during the
process to metallic copper, which is re-oxidised by subsequent heating in an air
current, is then ready to be used again. The E.M.F. of polarization is reduced
by about 06 volts by the employment of a copper oxide cathode.
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. The manufacture of white lead by, a, the production by electrolysis of a
solution of acetate of lead or other suitable salt of lead and a solution of caustic
ammonia or other alkali, , the treatment of the latter solution whilst separate from
the former, with carbonic acid and, e, the mixing of the two solutions, the one con-
taining the lead salt, and the other the carbonate of the alkali, thereby obtaining
white lead as a precipitate.
2. In the manufacture of white lead, by the precipitation of a solution of acetate
of lead or other suitable lead salt with a solution containing caustic ammonia or
other alkali and carbonate of the alkali, the latter substantially in the proportion
herein directed.
3. In the manufacture of white lead, and the production by electrolysis of a
soluble salt of lead, and caustic alkali, the provision in the electric circuit of an
electric meter from the indications of which the quantities of the two products can
be readily ascertained.
4. In the manufacture of white lead where a soluble acetate of lead or other
suitable salt of lead is precipitated with a solution containing carbonate of ammonia
or other alkali, the treatment of the liquid after the precipitate has been separated
with chromic acid thereby producing chrome, and at the same time rendering the
liquid more suitable for use in the production of a soluble salt of lead by means of
electrolysis.
Dated this 20th day of December 1892.
S. Z. DE FERRANTI.
JOHN H. NOAD.