CERTAIN IMPROVEMENTS IN MANUFACTURING WHITE LEAD
Year: 1838

page_text: TO ALL TO WHOM THESE PRESENTS SHALL COME, I, THOMAS
ROBERT SEWELL, of Carrington, in the County of Nottingham, Lace Manu-
facturer, send greeting.
WHEREAS Her present most Excellent Majesty Queen Victoria, by Her
Royal Letters Patent under the Great Seal of Great Britain, bearing date at
Westminster, the Fourteenth day of July, in the second year of Her reign,
and in the year of our Lord One thousand eight hundred and thirty-eight,
did, for Herself, Her heirs and successors, give and grant unto me, the
said Thomas Robert Sewell, Her especial license, full power, sole privilege
and authority, that I, the said Thomas Robert Sewell, my executors, admi-
nistrators, and assigns, or such others as I, the said Thomas Róbert 'Sewell,
my executors, administrators, or assigns, should at any time agree with, and
no others, from time to time and at all times during the term of years
therein mentioned, should and lawfully might make, use, exercise, and vend,
within England, Wales, the. Town of Berwick-upon-Tweed, and also all
Her Majesty's Colonies and Plantations abroad, my Invention of "CERTAIN
IMPROVEMENTS IN MANUFACTURING WHITE LEAD;" in which said Letters Patent
is contained a proviso, obliging me, the said Thomas Robert Sewell, by an
instrument in writing under my hand and seal, particularly to describe and
ascertain the nature of my said Invention, and in what manner the same is
to be performed, and to cause the same to be inrolled in Her Majesty's
High Court of Chancery within six calendar months next and immediately

page_text: after the date of the said in part recited Letters Patent, as in and by the
same, reference being thereunto had, will more fully and at large appear.
NOW KNOW YE, that in compliance with the said proviso, I, the said
Thomas Robert Sewell, do hereby declare that the nature of my said Inven-
tion, and the manner in which the same is to be performed, is particularly
described and ascertained in and by the following description thereof, reference
being had to the Drawings hereunto annexed, and to the letters and figures
marked thereon (that is to say):-
My Invention of improvements in manufacturing white lead consist in the
four following particulars:-First, a peculiar mode of manufacturing an oxide
of lead, which will be found more suitable for conversion into white lead than
those oxides known in commerce under the names of litharge and massicot.
Second, the production of a superior quality of white lead, into the com-
position of which a larger proportion of metallic lead, or a smaller proportion
of carbonic acid enters, than into an equal weight of carbonate of lead pro-
duced the ordinary modes of precipitation.
Third, the employment of carbonic acid obtained in a state which is better
adapted to the manufacture of white lead, than that evolved in the combustion
of charcoal or other carbonaceous matters in atmospheric air.
And fourth, a superior mode of operating in order to abstract from the
white lead the matters with which it may be in a state of mixture at the
time of its production.
of
The mode in which I manufacture the oxide of lead forming the first head
my Invention is thus:-I take the partially oxidized lead obtained in the
ordinary mode of making red lead, at that point of the process which imme-
diately precedes its introduction into the oven to be converted into red lead.
This preparation I have found to consist of a portion of metallic lead, pro-
toxide of lead, and some red lead; I place these materials in an oven,
similarly constructed to those usually employed in manufacturing red lead, in
which oven or other convenient receptacle I submit it to a moderately red
heat for about three or four hours. During this time it must be frequently
stirred with an iron rake or other suitable apparatus, in order to expose all
the parts equally to the action of the heat. This process of heating, owing
to the high temperature, instead of converting the materials into red lead,
decomposes all the particles of the red lead, oxidizes the metallic lead, and
brings the whole to the state of protoxide of lead, which is the substance
required. Whilst the protoxide is in this highly heated state, it is to be expe-
ditiously removed from the oven into a vessel, and closed up from the action
of the atmosphere until cold, when it has become fit for use.

page_text: I have two modes of effecting the second head of my Invention, either of
which I can employ. One of these modes is by precipitating the white lead
from solutions of oxide of lead, by means of alkali or alkalies in combination
with proper proportions of carbonic acid; the other is by precipitating white
lead from solutions of oxide of lead, by means of carbonic acid obtained in
manner herein-after to be described under the third head of my Invention.
In order to precipitate white lead by the first-mentioned method, I take
a quantity of protoxide of lead dissolved either in dilute nitric or acetic acid,
which solution may be either in the state of dinitrate, trisnitrate, diacetate, or
trisascetate of lead, the two latter I prefer; which being substances well
known to chemists need no further description. To any one of these I add
potash, soda, or ammonia, (which I prefer to be in a state of solution) in
quantity just sufficient to neutralize the acid of the solution of oxide, and
which alkaline materials must be previously in combustion, with as much
carbonic acid as will be sufficient to convert the oxide of lead into dicarbo
nate of lead, but not enough to convert that oxide into carbonate of lead.
To ensure a similar result when I employ the carbonic acid in the state
described under the third head of my Invention, I pass such carbonic acid
through a mixture of oxide of lead, in a solution of acetic acid or acetate of
lead, or. through a solution of diacetate of lead, or of trisacetate of lead, or.
through a mixture of any of these materials, and agitate the mixture during
the passage of the gas, but stop the supply of carbonic acid in a very few
minutes after the liquid arrives at such a state as would produce an acid
reaction upon blue litmus paper when dipped into it.
Under the third head of my Invention, the carbonic acid which I employ
may be obtained from either of the five different combinations of materials
about to be described. First, one part of charcoal, coke dust, or any other
similar carbonaceous matters, with about seven parts of sulphate of lime, well
ground and intimately mixed together; second, one part of charcoal or coke
dust, &c., with about ten parts of sulphate of barytes, well ground and mixed, as
above; third, one part of charcoal, &c., with about eight parts of sulphate of
strontia, well ground and mixed; fourth, three parts of charcoal, &c., with about
fifty parts of carbonate of lime and one hundred and twenty parts of sulphuret
of lead, well ground and mixed. Either of the above combinations of materials.
are to be placed in a retort of the same construction as those used for distilling
coal in the ordinary production of illuminating gas. The retort, being heated,
to a bright red, must be continued at that temperature as long as any gas can..
be generated, and the gas conducted into an hydraulic main, kept constantly.
supplied with water, and thence into a gasholder, from which it may be.

page_text: pumped or otherwise forced through a vessel of water, and brought into
contact with the materials about to be converted into white lead. The fifth
mode of producing carbonic acid gas, is by placing charcoal or coke, or other
similar carbonaceous matters broken into small pieces, in an earthen retort, and
when heated to a bright red, passing a current of steam through the materials
in the retort, which will cause the steam to be decomposed, and carbonic acid
gas to be produced, with small portions of other gases not injurious to the
subsequent operation of making white lead. These gases are to be collected
in a gasholder and applied in the manner before described.
The improved mode of washing white lead, which forms the fourth head
of my Invention, is effected under pressure in an apparatus of the kind
represented in the accompanying Drawings. White lead is produced in
various ways, but most frequently in a state of admixture with acids and
other matters, which it is necessary to remove by washing in water previously
to the white lead being dried and prepared for market. This operation of
washing has to be repeated several times in large volumes of water, and when
it is desired to recover the acids and other matters so washed away from the
lead, the very great quantity of water which must be evaporated in concen-
trating the matters contained in the water renders the operation difficult and
expensive. To obviate this inconvenience, I perform the washing of the lead
under either pneumatic or hydrostatic pressure, by which means I am enabled
to cleanse the lead effectually by a comparatively small quantity of water, and
also to save much of the time usually required for the lead to subside.
Fig. 1 of the Drawings represents in transverse section a strong cast-iron
vessel a, a, a, lined with copper, to prevent the white lead coming in contact
with the iron; and 6 is a strong cover to be placed upon it and fastened down
by screws; c being the receptacle in the vessel for the lead to be washed. Fig. 2
is a similar transverse section of the vessel with the lid attached, the vessel being
in this instance shewn in an inverted position. Fig. 3 is a longitudinal section
of the vessel, mounted in a strong wooden frame; and Fig. 4 is a similar
section, in which the vessel is seen inverted, as it would be while the washing
process was going on. A rebate is made round the vessel at d, d, for the
reception of packing, in order to render the vessel tight when the lid is fixed
upon it. A thick plate of copper e, e, perforated with holes, is attached to
the lid. A portion of this plate is shewn, both in plan and vertical section,
upon an enlarged scale at Figures 5 and 6. It will be perceived that the holes
are countersunk at that part which goes next the cover, and that such coun-
tersinking forms a communication with all the holes, and constitutes a shallow
passage between the plate and the cover. Copper pipes or tubes f, f, f, are

page_text: inserted into perforations through the cover, which pipes communicate with
the shallow passage behind the plate e, and are for the purpose of carrying off
the water filtered through the holes of the plate when the lead is under the
operation of washing. The vessel is supported in its frame by hollow axles
g and h, lined with copper. The axle g is to be stopped by a plug i, when the
apparatus is in action. The axle h has a tube k passed through it for the
purpose of conducting a current of water from the pipe l, the pipe and tube
k being connected by a stuffing box m, and at the end of the tube k there is a
bent nozzle, which directs the current of water. The vessel having been filled
with the white lead, and the lid fixed on, as shewn in Fig. 3, it must be
turned over into the position represented at Fig. 4, which may be done by
means of a toothed wheel taking into a pinion turned by a winch, or by any
other convenient means. Water being now passed through the pipe 1, by
means of a force-pump will, by the nozzle n, be thrown upon the top of the
white lead in the vessel, and be forced through the lead and through a filtering
material o, o, on the face of the plate e, and by means of the holes in the plate
e, will rush with great rapidity into the shallow passage behind, and be dis-.
charged by the pipes f, f, f, out of the vessel. This current of water through
the white lead in the vessel must be continued until the water is discharged in
a pure state. The white lead by this operation will be found to have been
compressed into a compact state at the lower part of the vessel; it is now
therefore only necessary to draw out the plug, and to discharge such portion of
water as may remain upon the lead. The vessel is then to be turned over into
its former position, shewn at Fig. 3, and the shaft p brought down and keyed
to the cover, when after withdrawing the holding screws, the lid may be raised
by turning the screw box q, which will cause the shaft p to lift the lid up, and
allow the white lead to be removed from the vessel.
I would lastly observe, that I do not intend to confine myself to the par-
ticular form or construction of vessel for washing described above, as any
other convenient form or construction may be employed if capable of washing
the white lead under pneumatic or hydrostatic pressure.
In witness whereof, I, the said Thomas Robert Sewell, have hereunto set
my hand and seal, this Fourteenth day of January, in the year of
our Lord One thousand eight hundred and thirty-nine.
THOS ROBT (L.S.) SEWELL.

page_text: AND BE IT REMEMBERED, that on the Fourteenth day of January, in
the second year of the reign of Her Majesty Queen Victoria, the said Thomas
Robert Sewell came before our said Lady the Queen in Her Chancery, and
acknowledged the instrument aforesaid, and all and every thing therein con;
tained and specified, in form above written.. And also the instrument aforesaid
was stamped according to the tenor of the Statute made in the fifty-fifth year
of the reign of His late Majesty King George the Third..
Inrolled the Fourteenth day of January, One thousand eight hundred and
thirty-nine.