IMPROVEMENTS IN THE MANU- FACTURE OF WHITE LEAD, AND APPARATUS EMPLOYED THEREIN
Year: 1877

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 MANU-
FACTURE OF WHITE LEAD, AND APPARATUS EMPLOYED THEREIN."
Sealed the 21st August 1877, and dated the 4th April 1877.
PROVISIONAL SPECIFICATION left by the said John Cowdery Martin at the
Office of the Commissioners of Patents on the 4th April 1877.
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."
I mix or grind oxide of lead with white lead produced by precipitation, or with
other white lead that may be deficient in body or density, or which requires an
undue quantity of oil for conversion by grinding into paint.
The lead oxide may be the black or grey suboxide produced by the abrasion of
the surface of metallic lead exposed in a dry or wet condition to the atmosphere
within a revolving cylinder or case, or it may be the oxide caused by the decom-
position of carbonate of lead by heat in a partially closed retort, but other oxide of
lead may be used.
I produce the precipitated white lead by any of the well-known processев,
either from litharge or other lead oxide, or directly from metallic lead. When
operating upon the last I reduce the lead to a condition for exposing a large
amount of surface to the atmosphere by causing it to fall in a melted state in small
regulated streams or drops upon a rapidly revolving cylinder kept cool by water
circulating within it through hollow journals. The metallic lead so divided I spread
upon racks one above another, over and through which by an intermittent move-
ment a solution of acetate of lead in water is caused to flow, white lead being
precipitated from such solution by the action of carbonic acid gas. I separate the
white lead from the solution by subsidence, or by passing it through a filter press,
or by forcing it under and through a cloth supported by a grooved and perforated
false bottom placed in a vat or vessel, and I wash the white lead by keeping it
agitated and forcing water through it while under a similar false bottom placed in
a senarate vessel.

page_text: I further produce white lead by passing a current of carbonic acid into water
with or without the addition of acetic acid or acetate of lead in solution, and
containing finely divided oxide of lead produced by the abrasion of metallic
lead exposed alternately to the action of water or the lead solution, and to the
atinosphere.
SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said John Cowdery Martin in the Great Seal Patent Office on the 4th
October 1877.
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."
I mix or grind oxide of lead with white lead produced by precipitation or with
other white lead that may be deficient in body or density, or which requires an
undue quantity of oil for conversion by grinding into paint.
The lead oxide may be the black or grey suboxide produced by the abrasion of
the surface of metallic lead exposed in a dry or wet condition to the atmosphero
within a revolving cylinder or case, or it may be the oxide caused by the decom-
position of carbonato of lead by heat in a partially closed retort, but other oxide of
lead may be used.
I produce the precipitated white lead by any of the well-known processes, either
froin litharge or other lead oxide, or directly from metallic lead. When operating
upon the last I reduce the lead to a condition to expose a large amount of surface
to the atmosphere by causing it to fall in a melted state in small regulated streams
or drops upon a rapidly revolving cylinder kept cool by water circulating within it
through hollow journals. The metallic lead so divided I spread upon racks one
above another, over and through which by an intermittent movement a solution
of acetate of lend in water is caused to flow, white lead being precipitated from
such solution by the action of carbonic acid gas. I separate the white lead from
the solution by subsidence, or by passing it through a filter press, or by forcing
it under and through a cloth supported by a grooved and perforated false bottom
placod in a vat or vessel, and I wash the white lead by keeping it agitated and
forcing water through it while under a similar false bottom placed in a separate
vessel.
I further produce white lead by passing a current of carbonic acid into water
with the addition of acetic acid or acetate of lead in solution, and containing
finely divided oxide of lead produced by the abrasion of metallic lead exposed
alternately to the action of water or the lead solution, and to the atmosphere.
White lead as hitherto manufactured by precipitation is, as is well known, of
less specific gravity than stack made lead, and requires a larger per-centage of oil
for conversion by grinding into paint, is deficient in spreading and covering pro-
perties, and liable to harden in the casks instead of to improve by keeping, as is
the case with well-made stack lead.
I have found, however, that all the properties of stack made lead may be imparted to
precipitated lead, and to effect this I prepare a peculiar hydrated suboxide of lead
produced by the abrasion of small granulated pieces of metallic lead enclosed
within a revolving case perforated to admit the air and produce oxidation. I
prefer the case to be of a square form of section revolving on its axis longitudinally,
a stream of water passing into it through hollow bearings on which it revolves,
and passing out through the perforations carries with it the suboxide; or instead
of a stream of water passing through the case, the latter may be made to revolve
partly in water.
Any other means of producing this oxide by agitating particles of metallic lead

page_text: in contact with the atmosphere, or by alternate exposure to the atmosphere and to
water, may be employed. The suboxide, which is of a black or grey colour, rapidly
subsides from water containing it, and from which it is removed and dried; it will be-
come more highly oxidized, and pass to a yellow colour if exposed too freely to the
atinosphere with agitation and with an insufficient amount of water to carry it
away this I endeavour to avoid. I prefer that the precipitated lead to be operated
upon should contain a slight excess of carbonic acid over stack lead, average samples
of which appear to consist of two parts of neutral carbonate to one of hydrated
oxide; this composition is not absolutely essential, but soft lead may be produced
by it, and it assists the subsequent combination.
I mix under pressure or grind with the lead in a dry condition one-half per cent.
or less by weight of the suboxide. I have found 8 lbs. impart to a ton of pre-
cipitated lead of the above composition all the properties of stack made lead, the
the crystaline particles appearing to be broken, and to have become amorphous, and
the bulk reduced after treatment, so that 166 parts by weight would occupy no
more space than 114 required before, the lead suboxide appearing to have entored
into combination with the carbonic acid, and to have become converted into white
lead with the due proportion of hydrated oxide to the neutral carbonate, as exists
in white lead of the ordinary formation.
have described the manner of producing the suboxide which I have found gives
the best results, but other oxides of lead will produce an effect more or less
analagous, the lower or suboxides (as the black or grey) producing the botter offect,
as they become more easily hydrated, and pass into a carbonate in a dry or nearly
dry state.
The superior oxides (as the red) produce the least effect, and their presence in
the lead would be generally visible, owing to imperfect combination, and as they
approach the orange or red colour would be liable to act as a drier to the ground
paint, causing it to harden and deteriorate in keeping.
I sometimes produce and use a grey or black suboxide of lead by treating white
lead in a closed or partially closed retort composed of iron or clay entirely or almost
entirely excluding the air, leaving a sinall aperture for the escape of the carbonic
acid gas, but any other way of producing the black or grey suboxido may be
employed.
An excess of oxide of lead may be produced in white lead by drying or heating
it exposed to the atmosphere, and driving off the carbonic acid at a high tempera-
ture, and this may be ground into the lead, and thus increase its specific gravity;
but in that process the quantity of the oxide is not readily under control, and is
liable to approach the red or orange coloured oxide produced by heat, which have
the defects above stated.
I make white lead for subsequent treatment by the suboxide by any of the well-
known processes of precipitation, but I prefer to make it as follows:-I spread
metallic lead prepared to expose as large a surface as possible upon trays or racks,
having spaces or openings in the bottom, and fitted between the racks with moveable
shutters to regulate the amount of atmospheric air passing over the lead. The lead
is spread to the thickness of from one to two feet upon each, and over this I cause
The number of racks or
to flow a stream of water containing acetic acid.
trays one above another is regulated by the quantity of the lead solution passing
over, and I direct the solution to each part of the lead, so that it shall wash away
the oxide from the surface so soon as formed. I effect this by making the racks of
an oblong form, and a perforated gutter (composed of wood or other suitable
material placed on wheels, and extending over the whole length of the trays, and
into which I pump the solution) is made to move slowly over the surface of the
upper rack or tray with an alternate to-and-fro movement by means of a connecting
rod fitted to each end of the gutter, and attached to two endless articulated metal
or other bands passing each over two pulleys fixed upon the ends of two shafts
working between the connecting rods, the distance between the pullies at each end
of the shafts from the outer edge of the one to the outer edge of the other being

page_text: equal to the distance the gutter is required to traverse; the faces of the pullies
may be fitted with projections fitting into holes or spaces in the band, or provided
with other means to prevent its slipping and ensure a regular movement.
Figures 8 and 9 shew an end elevation and plan respectively.
a, a, a, a, are the trays containing the lead c, c, c; b, b, the gutter for distributing
the solution; d, d, the pullies on the ends of the shafts driving the endless bands
to which are attached the connecting rods g, g, giving motion to the gutter;
h is the pulley communicating motion; i is the pipe carrying the solution from the
pumps to the gutter and over the lead; is the pipe carrying the solution from
the lead to the precipitating vats; is one of a series of shutters by which the
spaces between the trays can be closed.
Instead of pullies and endless bands for communicating motion to the gutter
simple crank arms or discs and crank pins, or other suitable means may be employed.
The solution flowing over the lead passes to vats or vessels placed beneath and
filling them alternately; a current of carbonic acid gas is passed through each, pre-
cipitating the white lead, as is well understood. The precipitated lead is then
removed from the solution by subsidence, or by forcing the solution containing it
through an ordinary filter press, or by preference one to be presently described.
For precipitating the lead I employ two or more vats, but I prefer to employ three,
and I pass the gas into each or all at the same time running the charged lead solution
into each alternately, and pumping the solution containing the precipitated lead also
from each alternately, taking care to stop the flow into the vat before commencing
to pump from it. I am enabled by this means to more readily obtain a softer lead,
which combines better with the lead oxide in the subsequent operations than when
one precipitating vat is used, in which the solution flowing from the metallic lead
and the precipitated white lead pass into and out of the vat at the same time, as I
find the lead precipitated in presence of a solution highly charged with basic salt
of lead is harder, and does not combine so well as when the action has been con-
tinued slightly longer upon the solution, and it contains less basic salt.
After the lead is separated the solution is again caused to flow over the lead, and
the several operations are repeated indefinitely.
The filter presses I prefer to use are composed of several sufficiently strong
frames of wood of the same size and thickness internally as the block of lead
required, and over and between each are placed grooved boards. A groove to
contain a rod is also formed in both sides of the frame, as shown in section at a, a,
Figure 1, and strips of cloth cut and carefully joined to the form shown at Figure 2
are firmly attached by the edges b, b, b, b, to the inner edge of each side of the
frame, as shown at a, Figure 1. This is stretched outwards over the frame, covering
the grooves a, a, a, a, as shown at Figure 3. A second cloth covering the entire
frame and marginal strip is placed over this, and the two are pressed into the
groove a, a, and held by the rod d, shown in section at Figure 1, fitting into the
groove upon them; both parts of the cloth are folded back over the rod, and appear
as shown at Figure 4, and both sides of the frame having cloths a perfectly closed
space of the thickness of the block of lead required is formed. I have found 3
inches in thickness gives good results.
c, e, e, e, Figure 4, are loops of string fitting over pins to retain the folded cloth
in position until closed by the grooved boards.
Several of these closed frames, covered by the grooved boards, are placed side
by side, and firmly bolted together in the ordinary manner of a filter press, and the
solution containing the lead is forced through a pipe e¹ into each of the frames, and
passes out through the cloths, the lead being retained. When' the frames are filled
and the lead pressed sufficiently hard, the latter is removed and placed in a tub or
vessel fitted with a revolving agitator after the manner of a pug mill to reduce the
pressed lead to such a consistency with water as will enable it to flow through a
pipe into the washing apparatus, shown in section at Figure 5, and which consists
of a vessel composed of two parts. The lower part, containing a revolving agitator f
is by preference of semicircular or segmental form, and capable of holding about a

page_text: ton of white lead, which I have found to be a convenient quantity to wash at one
operation. Into this the diluted white lead is run, the upper part being closed by
cloths fitting over rods placed in grooves f, f, in the edge of the wood forming
the vessel in the manner described for closing one side of the frames used for
pressing the lead, as shown at Figure 1; the shaft of the agitator which is placed
horizontally the whole length of the apparatus passes through the side, and is driven
from without by a pulley, or otherwise. The upper part of the washing apparatus
has a bottom composed of boards well supported to resist pressure, and containing
grooves on the lower side similar to the press boards, and also having holes from
the grooves passing quite through, as shown at g, g, g, g, Figure 5, this being placed
over the cloth is firmly held by bolts and cross pieces to the lower part, as shown
at h, h, h, h, Figure 5, but is capable of being readily removed. A pipe i from a forco
pump or from a tank of water placed sufficiently above to give the requisite pressure
leads into the lower part of the vessel. I have found a pressure equal to a head of
water of about 18 feet in height answer well.
The lead to be washed being sufficiently diluted with water and run into the
vessel by the pipe, Figure 5, the agitator is set working, and when required a
small quantity of sulphuric acid, soda crystals, or chloride of sodium in solution, or
other suitable substance which will cause the lead to separate freely from the water
is introduced by means of the pipe and funnel 1, Figure 5, and a small quantity may
be withdrawn by the pipe m to ascertain that the lead separates freely beforo
admitting the washing water. The several pipes are each fitted with suitable
cocks. Water is then admitted from the tank above, is diffused through the lead
by the agitator, and passes through the cloth and the holes in the false bottom
above, running off by an opening and pipe n in the side of the vessel, the white lend
being held back by the cloth.
When no traces of lead salt are found in the water, or the lead is sufficiently
washed (which will occur in from half an hour or an hour, according to the quantity
of water used) the water supply is shut off, and the washed lead with the remaining
water is pumped by the pipe o through a filter press similar to that before described,
from which the pressed lead is removed and dried in the ordinary manner. It is
necessary to open the pipe 7 leading into the apparatus to admit air before removing
the contents after washing, or the cloth may be forced down by the atmospheric
pressure upon the agitator.
I do not confine myself to the method above described for fixing a false bottom
supporting a cloth over an agitator when washing white lead, as any other con-
venient manner of securing a cloth or its equivalent by a false bottom fixed over an
agitator and capable of holding back the lead while the water passes through may
be employed.
I melt the metallic lead for conversion into white lead in an ordinary melting pot
having an aperture near the bottom closed by a plug, and I run the lead from this
into an iron gutter containing holes, such gutter being kept hot by gas or other
suitable means and placed over a revolving cylinder of iron or other suitable material
kept cool by water passing through it, and it may, if required, bo occasionally
polished with black lead to prevent adhesion of the metal. The drops of lead in
falling from the holes become flattened and cooled on striking the cylinder, and are
thrown off by the centrifugal force generated into a trough containing water placed
beneath. The metallic lead is by this operation rapidly converted into small thin
flakes, exposing a large surface to the oxidizing influence of the atmosphere.
Sometimes I pour the lead into the perforated gutter by means of a ladle in place
of running it directly in by means of the plug and pipe described.
Figures 6 and 7 show a plan and sectional elevation of the apparatus of which a
is the pipe leading from the melting pot; b, the perforated gutter; c, the revolving
cylinder; and d, the trough beneath; shows the inlet and the outlet of the
water passing through the cylinder, and which also supplies the trough, an overflow
pipe carrying it away.
Instead of keeping the metallic lead stationary, as above described, and pumping

page_text: or causing the solution to be in motion over it, I sometimes keep the solution
stationary and move the lead by placing the latter within revolving cylinders, or
cases having perforations to admit the air, such cylinders or cases being composed of
any material which will not decompose or injure the solution, which may be a
solution of the acetate or other suitable salt of lead. I revolve these cylinders when
partially immersed in the solution, or I move the lead in any other way that will
expose it alternately to the solution and to the atmosphere. The solution becomes
very rapidly charged with lead oxide, when it is run off into vats and treated with
carbonic acid, the white lead being separated precisely as above described when the
metallic lead is to be stationary and the solution passes over it.
Having now described the nature of the said Invention, and the manner in which
the same is to or may be carried into effect, I would have it understood that I do
not claim as any part of my Invention the production of white lead by precipitation
from a solution passing over metallic lead, as I am well aware it is known and
practised, but what I do claim as the features of novelty and intend to be secured
by the within in part recited Letters Patent are,
Firstly. The treatment of precipitated white lead or other white lead requiring to
be increased, in specific gravity with oxide of lead, as herein-before described and
for the purpose set forth.
Secondly. The production of the oxide of lead by the alternate exposure to the
atmosphere and abrasion of metallic lead either in a wet or dry state, or by heating
carbonate of lead in a closed or partially closed retort, substantially as described
and for the purpose set forth.
Thirdly. The construction and arrangement of the frames and cloths between the
grooved boards of the filtering presses, substantially as herein-before described and
illustrated in Figures 1, 2, 3, and 4 of the Drawings.
Fourthly. The washing apparatus constructed, arranged, and adapted, sub-
stantially as herein-before described and illustrated in Figure 5 of the Drawings.
Fifthly. The combination of the trays or racks containing the metallic lead with
the traversing gutter, arranged and adapted substantially as hercin-before described
and illustrated in Figures 8 and 9 of the Drawings, and for the purposes set forth.
Sixthly. Passing the solution flowing from the metallic lead alternately to two or
more vessels for precipitation, as and for the purposes described.
Seventhly. Placing metallic lead in small pieces within perforated cylinders, and
revolving them when partly immersed in a solution of acetate or other suitable salt
of lead, or otherwise exposing metallic lead in motion alternately to such solution
and to the atmosphere for the manufacture of white lead, as described.
Eighthly. The apparatus for reducing the metallic lead to a subdivided condition,
substantially as herein-before described and illustrated in Figures 6 and 7 of the
Drawings for the manufacture of whito lead.
In witness whereof, I, the said John Cowdery Martin, have hereunto set my
hand and seal, this Third day of October, in the year of our Lord One
thousand eight hundred and seventy-sevon.

page_text: In the Matter of Letters Patent granted to John Cowdery Martin of 5 Upper
Hill Street, Richmond, in the County of Surrey for an Invention
of IMPROVEMENTS IN THE MANUFACTURE OF WHITE LEAD AND
APPARATUS EMPLOYED THEREIN " bearing date the Fourth day of April,
One thousand eight hundred and seventy seven N° 1300.
DISCLAIMER AND MEMORANDUM OF ALTERATION of parts of the
Specification of the said Letters Patent proposed to be entered by the said
John Cowdery Martin.
WHEREAS since the date of the said Letters Patent and of the filing of the
Final Specification of the same I the said John Cowdery Martin have ascertained
that doubts have arisen as to the novelty of parts of the Invention described and
claimed in the Specification of the said Patent and also that there are certain
inaccuracies in the said Specification and I am therefore desirous of amending the
said Specification by disclaiming certain parts thereof and making certain
corrections therein.
I the said John Cowdery Martin therefore for the reasons aforesaid do hereby
alter and amend the Specification as follows, that is to say:-
In the printed Specification published by the Commissioners of Patents at page
line 4, I strike out the numeral "8" and substitute therefor the numeral "6" and
in the same line I strike out the numeral "9" and substitute therefor the
numeral "7."
At the same page line 11 after the word "closed" I add the words "The said
letter is omitted but should be marked in Figure 6 on one of the vertical
shutters."
At page 4 line 38 I alter the letter of reference "
reference "c."
a " to the letter of
At page 5 line 28 I strike out the word "or" and substitute therefor the
word "* to."
At page 5 line 52 I strike out the numeral "6" and substitute therefor the
numeral "9" and in the same line I strike out the numeral "7" and substitute
therefor the numeral "8."
At page 6 lines 20 to 23 I strike out the whole of the second claim.
At the same page line 24 I alter the word "Thirdly" to "Secondly."
At the same page line 27 I alter the word "Fourthly" to "Thirdly.”
At the same page line 29 I alter the word "Fifthly" to "Fourthly."
At the same page line 31 I alter the numeral "8" to the numeral "6" and the
numeral "9" to the numeral "7."

page_text: At the same page lines 32 and 33 I strike out the whole of the sixth claim.
At the same page line 34 I alter the word "Seventhly" to "Fifthly."
At the same page line 36 I strike out the words "or otherwise exposing
metallic and substitute therefor the words "exposing such."
13
At the same page line 38 I strike out the word "Eighthly" and substitute
therefor the word "Sixthly." In the same line between the word "The” and
the word "apparatus" I insert the words "use of the."
At the same page
line 39 I strike out the numeral "6" and substitute therefor
the numeral "8 and in the same line I strike out the numeral "7" and
substitute therefor the numeral "9" after which alterations the Specification will
read as follows:-
I mix or grind oxide of lead with white lead produced by precipitation or with
other white lead that may be deficient in body or density, or which requires an
undue quantity of oil for conversion by grinding into paint.
The lead oxide may be the black or grey suboxide produced by the abrasion of
the surface of metallic lead exposed in a dry or wet condition to the atmosphere
within a revolving cylinder or case, or it may be the oxide caused by the decom-
position of carbonate of lead by heat in a partially closed retort, but other oxide
of lead may be used.
I produce the precipitated white lead by any of the well-known processes, either
from litharge or other lead oxide, or directly from metallic lead. When operating
upon the last I reduce the lead to a condition to expose a large amount of surface
to the atmosphere by causing it to fall in a melted state in small regulated streams
or drops upon a rapidly revolving cylinder kept cool by water circulating within it
through hollow journals. The metallic lead so divided I spread upon racks one
above another, over and through which by an intermittent movement a solution of
acetate of lead in water is caused to flow, white lead being precipitated from such
solution by the action of carbonic acid gas. I separate the white lead from the
solution by subsidence, or by passing it through a filter press, or by forcing it
under and through a cloth supported by a grooved and perforated falso bottom
placed in a vat or vessel, and I wash the white lead by keeping it agitated and
forcing water through it while under a similar false bottom placed in a separate
vessel.
I further produce white lead by passing a current of carbonic acid into water with
the addition of acetic acid or acetate of lead in solution, and containing finely
divided oxide of lead produced by the abrasion of metallic lead exposed alternately
to the action of water or the lead solution, and to the atmosphere.
White lead as hitherto manufactured by precipitation is, as is well known, of less
specific gravity than stack made lead, and requires a larger percentage of oil for
conversion by grinding into paint, is deficient in spreading and covering properties,
and liable to harden in the casks instead of to improve by keeping as is the cuse
with well-made stack lead.
I have found, however, that all the properties of stack made lead may be
imparted to precipitated lead, and to effect this I prepare a peculiar bydrated sub-
oxide of lead produced by the abrasion of sinall granulated pieces of metallic lead
enclosed within a revolving case perforated to admit the air and produce oxidation.
I prefer the case to be of a square form of section revolving on its axis longitu-
dinally, a stream of water passing into it through hollow bearings on which it
revolves, and passing out through the perforations carries with it the suboxide; or
instead of a stream of water passing through the case the latter may be made to
revolve partly in water.
Any other means of producing this oxide by agitating particles of metallic lead
in contact with the atmosphere, or by alternate exposure to the atmosphere and to
water, may be employed. The suboxide, which is of a black or grey colour, rapidly
subsides from water containing it, and from which it is removed and dried; it will
become more highly oxidized, and pass to a yellow colour if exposed too freely to
the atmosphere with agitation with an insufficient amount of water to carry it

page_text: away; this I endeavour to avoid. prefer that the precipitated lead to be operated
upon should contain a slight excess of carbonic acid over stack lead, average
samples of which appear to consist of two parts of neutral carbonate to one
of hydrated oxide; this composition is not absolutely essential, but soft lead may
be produced by it, and it assists the subsequent combination.
I mix under pressure or grind with the lead in a dry condition one half per cent.
or less by weight of the suboxide. I have found 8 lbs. impart to a ton of pre-
cipitated load of the above composition all the properties of stack made lead, the
crystaline particles appearing to be broken, and to have become amorphous and
the bulk reduced after treatment, so that 166 parts by weight would occupy no
incre space than 114 required before, the lead suboxide appearing to have entered
into combination with the carbonic acid, and to have becoine converted into white
lead with the due proportion of hydrated oxide to the neutral carbonate, as exists
in white lead of the ordinary foriuation.
I have described the manner of producing the suboxide which I have found gives
the best results, but other oxides of lead will produce an effect more or less
analagous, the lower or suboxides (as the black or grey) producing the better effect,
as they become more easily hydrated, and pass into a carbonate in a dry or nearly
dry state.
The superior oxides (as the red) produce the least effect, and their presence in
the le would be generally visible, owing to imperfect combination, and as they
appro the orange or red colour would be liable to act as a drier to the ground
paint, causing it to harden and deteriorate in keeping.
I sometimes produce and use a grey or black suboxide of lead by treating white
lead in a closed or partially closed retort composed of iron or clay entirely or
almost entirely excluding the air, leaving a small aperture for the escape of the
carbonic acid gas, but any other way of producing the black or grey suboxide may
be employed.
An excess of oxide of lead may be produced in white lead by drying or heating
it exposed to the atmosphere, and driving off the carbonic acid at a high temperaturo,
and this may be ground into the lead, and thus increase its specific gravity; but in
that process the quantity of oxide is not readily under control, and is liable to
approach the red or orange coloured oxide produced by heat, which have the defects
above stated.
I make white lead for subsequent treatment by the suboxide by any of the well-
known processes of precipitation, but I prefer to make it as follows;--I spread
metallic lead prepared to expose as large a surface as possible upon trays or racks,
having spaces or openings in the bottom, and fitted between the racks with
moveable shutters to regulate the amount of atmospheric air passing over the lead.
The lead is spread to the thickness of from one to two feet upon each, and over
this I cause to flow a stream of water containing acetic acid. The number of racks
or trays one above another is regulated by the quantity of the lead solution passing
over, and I direct the solution to each part of the lead, so that it shall wash away
the oxide from the surface so soon as formed. I effect this by making the racks of
an oblong form, and a perforated gutter (composed of wood or other suitable
material placed on wheels, and extending over the whole length of the trays, and
into which I pump the solution) is made to move slowly over the surface of the
upper rack or tray with an alternate to and fro movement by means of a connecting
rod fitted to each end of the gutter, and attached to two endless articulated metal
or other bands passing each over two pulleys fixed upon the ends of two shafts
working between the connecting rods, the distance between the pullies at each end
of the shafts from the outer edge of the one to the outer edge of the other being
equal to the distance the gutter is required to traverse; the faces of the pullies
may be fitted with projections fitting into holes or spaces in the band, or provided
with other means to prevent its slipping and ensure a regular movement.
Figures 6 and 7 show an end elevation and plan respectively.
u, a, a, a, are the trays containing the lead c, c, c; b, b, the gutter for distributing

page_text: the solution; d, d, the pullies on the ends of the shafts driving the endless
bands ff, to which are attached the connecting rods g, g, giving motion to the
gutter; his the pulley communicating motion; i is the pipe carrying the solution
from the pumps to the gutter and over the lead; k is the pipe carrying the solution
from the lead to the precipitating vats; is one of a series of shutters by which
the spaces between the trays can be closed. The said letter is omitted but
should be marked in Figure 6 on one of the vertical shutters.
Instead of pullies and endless bands for communicating motion to the gutter,
simple crank arms or discs and crank pins, or other suitable means may be
employed.
The solution flowing over the lead passes to vats or vessels placed beneath, and
filling them alternately a current of carbonic acid gas is passed through each,
precipitating the white lead, as is well understood. The precipitated lead is then
removed from the solution by subsidence, or by forcing the solution containing it
through an ordinary filter press, or by preference one to be presently described.
For precipitating the lead I employ two or more vats, but I prefer to employ
three, and I pass the gas into each or all at the same time running the charged
lead solution into each alternately, and pumping the solution containing the
precipitated lead also from each alternately, taking care to stop the flow into the
vat before commencing to pump from it. I am enabled by this means to more
readily obtain a softer lead, which combines better with the lead oxide in the
subsequent operations than when one precipitating vat is used, in which the
solution flowing from the metallic lead and the precipitated white lead pass into
and out of the vat at the same time, as I find the lead precipitated in presence of
a solution highly charged with basic salt of lead is harder, and does not combine so
well as when the action has been continued slightly longer upon the solution, and
it contains less basic salt.
After the lead is separated the solution is again caused to flow over the lead, and
the several operations are repeated indefinitely.
The filter presses I prefer to use are composed of several sufficiently strong
frames of wood of the same size and thickness internally as the block of lead
required, and over and between each are placed grooved boards. A groove to
coutain a rod is also formed in both sides of the frame, as shown in section at a, a,
Figure 1, and strips of cloth cut and carefully joined to the form shown at Figure 2.
are firmly attached by the edges b, b, b, b, to the inner edge of each side of the
frame, as shown at c Figure 1. This is stretched outwards over the frame, covering
the grooves a, a, a, a, as shown at Figure 3. A second cloth covering the entire
frame and marginal strip is placed over this, and the two are pressed into the
groove a, a, and held by the rod d shown in section at Figure 1, fitting into the
groove upon them; both parts of the cloth are folded back over the rod, and
appear as shown at Figure 4. and both sides of the frame having cloths a perfectly
closed space of the thickness of the block of lead required is formed. I have
found 3 inches in thickness gives good results.
e, e, e, e, Figure 4, are loops of string fitting over pins to retain the folded cloth
in position until closed by the grooved boards.
Several of these closed frames, covered by the grooved boards, are placed side
by side, and firmly bolted together in the ordinary manner of a filter press, and
the solution containing the lead is forced through a pipe e', into each of the frames,
and passes out through the cloths, the lead being retained. When the frames are
filled and the lead pressed sufficiently hard, the latter is removed and placed in a
tub or vessel fitted with a revolving agitator after the manner of a pug mill to
reduce the pressed lead to such a consistency with water as will enable it to flow
through a pipe into the washing apparatus, shown in section at Figure 5, and
which consists of a vessel composed of two parts. The lower part, containing a
revolving agitator is by preference of semicircular or segmental form, and capable
of holding about a ton of white lead, which I have found to be a convenient
quantity to wash at one operation. Into this the diluted white lead is run, the

page_text: upper part being closed by cloths fitting over rods placed in grooves f¹, f' in the
edge of the wood forming the vessel in the manner described for closing one side
of the frames used for pressing the lead, as shown at Figure 1; the shaft of the
agitator which is placed horizontally the whole length of the apparatus passes
through the side, and is driven from without by a pulley, or otherwise.
The upper part of the washing apparatus has a bottom composed of boards well
supported to resist pressure, and containing grooves on the lower side similar to
the press boards, and also having holes from the grooves passing quite through,
as shown at g, g. 9, g, Figure 5, this being placed over the cloth is firmly held by
bolts and cross pieces to the lower part, as shown at h, h, h, h, Figure 5, but is
capable of being readily removed. A pipe i from a force pump or from a tank of
water placed sufficiently above to give the requisite pressure leads into the lower
part of the vessel. I have found a pressure equal to a head of water of about
18 feet in height answer well.
The lead to be washed being sufficiently diluted with water and run into the
vessel by the pipe k, Figure 5, the agitator is set working, and when required a
small quantity of sulphuric acid, soda crystals, or chloride of sodium in solution,
or other suitable substance which will cause the lead to separate freely from the
water is introduced by means of the pipe and funnel L, Figure 5, and a small
quantity may be withdrawn by the pipe m, to ascertain that the lead separates
freely before admitting the washing water. The several pipes are each fitted with
suitable cocks. Water is then adinitted from the tank above, is diffused through
the lead by the agitator, and passes through the cloth and the holes in the false
bottom above running off by an opening and pipe n in the side of the vessel, the
white lead being held back by the cloth.
When no traces of lead salt are found in the water, or the lead is sufficiently
washed (which will occur in from half an hour to an hour according to the quantity
of water used) the water supply is shut off, and the washed lead with the
remaining water is pumped by the pipe o, through a filter press similar to that
before described, from which the pressed lead is removed and dried in the ordinary
manner. It is necessary to open the pipe leading into the apparatus to admit air
before removing the contents after washing, or the cloth may be forced down by
the atmospheric pressure upon the agitator.
I do not contine myself to the method above described for fixing a false bottom
supporting a cloth over an agitator when washing white lead as any other
convenient manner of securing a cloth or its equivalent by a false bottom fixed
over an agitator and capable of holding back the lead while the water passes
through may be employed.
I melt the metallic lead for conversion into white lead in an ordinary melting
pot having an aperture near the bottom closed by a plug, and I run the lead from
this into an iron gutter containing holes, such gutter being kept hot by gas or
other suitable means and placed over a revolving cylinder of iron or other suitable
material kept cool by water passing through it, and it may, if required, be
occasionally polished with black lead to prevent adhesion of the metal. The drops
of lead in falling from the holes become flattened and cooled on striking the
cylinder, and are thrown off by the centrifugal force generated into a trough
containing water placed beneath. The metallic lead is by this operation rapidly
converted into small thin flakes, exposing a large surface to the oxidizing influence
of the atmosphere.
Sometimes I pour the lead into the perforated gutter by means of a ladle in
place of running it directly in by means of the plug and pipe described.
Figures 9 and 8 show a plan and sectional elevation of the apparatus of which a
is the pipe leading from the melting pot; b, the perforated gutter ; c, the revolving
cylinder; and d, the trough beneath; f shows the inlet and g the outlet of the
water passing through the cylinder, and which also supplies the trough, an overflow
pipe carrying it away.
Instead of keeping the metallic lead stationary as above described, and pumping