CERTAIN IMPROVEMENTS IN THE MANUFACTURE OF WHITE LEAD
Year: 1837

page_text: TO ALL TO WHOM THESE PRESENTS SHALL COME, I, THOMAS
ROBERT SEWELL, of Carrington, in the Parish of Basford and County of
Nottingham, Lace Manufacturer, send greeting.
WHEREAS His late most Excellent Majesty King William the Fourth,
by His Royal Letters Patent, bearing date at Westminster, the Eleventh day
of January, in the seventh year of His reign, did, for Himself, His heirs and
successors, give and grant unto me, the said Thomas Robert Sewell, my exors,
admors, and assigns, and such others as I, the said Thomas Robert Sewell, shall
at any time agree with, & no others, His especial licence for the full power,
sole privilege and authority, to make, use, or exercise and vend, within England
and Wales, and the Town of Berwick-upon-Tweed, and in all His Majestie's
Colonies and Plantation abroad, my Invention of "CERTAIN IMPROVEMENTS
IN THE MANUFACTURE OF 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, to describe and ascertain the
nature of my said Invention, and in what manner the same is to be performed
and carried into effect, and to cause the same to be enrolled in His said
Majesty's High Court of Chancery within six calendar months next and
immediately after the date of the said in part recited Letters Patent, in
default of which the said Letters Patent, and all rights, priviledges, and benefits
therein mentioned, are totally to cease, determine, and become void.

page_text: NOW KNOW YE, that in compliance with the said proviso, I, the said
Thomas Robert Sewell, do hereby declare the nature of my said Invention,
and in what manner the same is to be performed and carried into effect, by
the following description or explanation thereof, reference being made to the
Drawings herennto annexed, and the letters and figures marked thereon,
that is to say:--
My Improvements in the Manufacture of White Lead consist, in the first
place, in a mode of combining oxygen with lead, by the agency of the com-
bustion of charcoal, for the purpose of producing a material or substance
commonly called or known to chemists as protoxide of lead, in connection
with a mode of preserving and applying the carbonic acid gas, generated by
the combustion, to the further purpose of carbonating protoxide of lead.
Secondly, in certain improved modes of operating for the purpose of
carbonating protoxide of lead, in order to produce the substance or pigment
called ceruse, or the white lead of commerce.
Thirdly, in the construction and arrangement of apparatus suited to perform
one or both of these operations separately or combined.
As respects the first head of my Invention, I place metallic or blue lead in
a suitable receptacle, where it is melted by the heated gases produced from
the combustion of charcoal, and oxydized by the oxygen of the undecom-
posed atmospheric air brought over its surface, by means of which operations
the lead becomes oxidized and rendered in a fit state for being converted into
the pigment called white lead, and the carbonic acid gas, instead of being allowed
to escape into the atmosphere immediately after passing over the lead, is
conducted through pipes by means of a pump to the vessel in which the
carbonating process is to be performed. As to the second head of the Inven-
tion, I place protoxide of lead, prepared as above and ground and washed (or
by any other process which may have rendered it fit for the purpose), in a
suitable vessel containing a solution of acetate of lead, or of acetic acid, or
any other suitable solvent of protoxide of lead, and pass through this mixture
a current of carbonic acid gas, for the purpose of agitating the mixture and
promoting the action of the solvent upon the oxide, and when a portion of
the oxide has become dissolved in the solvent, causing the carbonic acid gas
to unite with it, and to precipitate ceruse or white lead. The third head of
the Invention, the construction and arrangement of apparatus suited to the
purposes of the above operations, will be best understood by reference to the
accompanying Drawings, in which Fig. 1 is a longitudinal section of an
apparatus arranged to conduct the operation from the beginning to the end.
A furnace a, containing a quantity of ignited charcoal, is placed contiguous to

page_text: a vessel or trough b, b, formed of fire brick, which is shewn in transverse
section at Fig. 2. This vessel contains a quantity of metallic or blue lead c,
and is covered by a roof d, d, of fire brick, forming a very narrow channel as
a flue over the surface of the lead. The furnace is supplied with atmospheric
air from the open ashpit e below, and the oxygen and other gases, as well as
the carbonic acid gas generated from the combustion, pass in a heated state
through the vessel 6 over the surface of the lead, and in passing cause the
lead to melt. A quantity of cold air may be admitted, if necessary, at the
door f in front, for the purpose of regulating the temperature of the melted
lead, which should be kept at a low red heat during the operation. In the
passage of the gases over the surface of the melted lead c, oxygen enters into
combination with the lead and converts it into an oxide. The carbonic acid
and other gases proceeding onward descend into the chamber g, carrying with
them the oxide thus produced, which deposites on the floor at the bottom of
the chamber (and from thence may be removed, when necessary, by opening
the door h), whilst the gases pass up through the pipe i, i.
It will now be necessary to shew the means by which I produce a current of
air and gases through the furnace a, the lead vessel b, the chamber g, and the
pipe i, i, i. A tank of water is fixed in the masonry at k, k, and in this is
placed an inverted vessel 1, 1, supported by bars m. A perforated diaphragm
n, n, is fixed within this vessel l, which diaphragm may be covered with a
sheet of wire gauze for the purpose of causing the gases, which are to be
passed through the diaphragm, to be separated into very minute bubbles.
Pure water is delivered into the vessels / and / by a pipe from a cistern o,
which may continue flowing until the tank k is filled nearly up to its brim.
A wooden vessel p, p, p, (say about six feet diameter and six feet deep) is
furnished with a false bottom of wood q, which is perforated with holes each
of about an inch in diameter. This false bottom is placed a few inches
from the real bottom, forming a space j between them for the introduction of
the gases. Upon the upper surface of the false bottom a shed or diaphragm
of very closely woven canvass or wash leather, or other suitable porous sub-
stance, is tightly distended and secured in that situation, or perhaps a false
bottom of porous wood might answer the purpose. On this diaphragm I
place a quantity of protoxide of lead, say a ton weight, and then nearly
fill the vessel p with a solution consisting of about nine hundredweight of
acetate of lead, dissolved in about four or five times its weight of water, which
solution is intended as a menstruum for dissolving the protoxide of lead, and
becomes the vehicle for the chemical operation which is to follow; or, instead of
this solution, acetic acid or any other suitable solvent of lead may ] be employed,'

page_text: but I prefer that above mentioned.
Now in order to carry on the process of
making white lead by the apparatus under consideration I employ an air
pump, which is connected by pipes and chambers to the furnace a on one
side, and to the vessel p on the other side, as represented partly in section in
Fig. 1.
A pipe 8, 8, 8, leading from the upper part of the vessel ?, is connected
to the induction side of the air pump, and a pipe t from the eduction side
leads into a close air-tight vessel u, furnished with a weighted valve to regulate
the pressure within. From this vessel u a pipe v, having a regulating stop-
cock, communicates with the compartment j under the false bottom g in the
vessel p. The air pump r, which is constructed on the double-action prin-
ciple, is to be worked by a steam engine or other adequate means applied to
its piston, by the action of which the atmospheric air is drawn from the
vessel 1, through the pipe s, and forced through the pipe t. On a partial
vacuum being thus produced in the vessel 7, the water will rise in that vessel
and descend in the tank to the levels shewn in the Drawing, and on the
further action of the pump r atmospheric air, and the gases produced by
by combustion in the furnace a, will be drawn from the furnace over the
surface of the melted lead c, through the chamber g and pipe i into the water
in the vessel 1, and there these gases rising in bubbles through the water and
through the diaphragm n become washed and cooled before they ascend into
the upper part of the vessel, the water in the vessel 7 being kept continually
cool by a jet of cold water from the cistern o, the surplus water escaping by
the perpendicular pipe w and gage cock x, from whence it runs off into a
drain. In the progress of these gases from the furnace over the surface of
the melted lead the oxygen of that portion of the atmospheric air which has
not been decomposed by the combustion combines with the lead and converts
it into an oxide, which oxide, if not blown off by the draft into the chamber g
below, may be pushed forward by a rake and deposited in the bottom of the
chamber. And I would here remark, that if the operation should be found
not to have brought the lead completely into the state of a protoxide, the
material may be again placed in the trough b and be subjected to a repe-
tition of the same operation. The continued action of the pump r will
draw the gases from the upper part of the vessel through the pipe s, and
force them through the pipe t into the air vessel u, where the gases becoming
slightly compressed, the vessel will constitute a reservoir for supplying a
continuous current of the gases through the pipe v into the compartment j in
the bottom part of the vessel p. The gases are by these means made to rise
through the false bottom 9 of the vessel p, and through the diaphragm of close
canvass or wash leather, or other porous material, and in passing the gases

page_text: will be found to ascend in a multitude of streams of exceedingly minute
bubbles through the solution, agitating the particles of the protoxide of lead
as they pass, and assisting them to dissolve in the menstruum, in which progress
the carbonic acid gas enters into chemical combination with the protoxide
of lead held in solution, and causes it to precipitate in the form of ceruse or
white lead. In the event of the solution in the vessel p percolating thro' the
diaphragm into the compartment j, it will be necessary to afford the means
for its discharge in a lateral direction, otherwise the gases could not be
conveniently forced through the menstruum. For this purpose I apply a pipe y
the lower end of which communicates with the compartment ; under the false
bottom, and the upper end opens into the vessel p near its top. When the
elastic force of the gases in the vessel u are beginning to act through the
pipe v, the stopcock in the pipe y must be opened, which will allow the liquor
in the compartment ; to be forced up the pipe y by the pressure of the gases,
and when it has been thus discharged from the compartment the stopcock
must be closed, and the gases will then pass up through the menstruum, as
before described. This process must be continued until the whole of the
oxide has been dissolved, which may be known by the whiteness of the
precipitate, and if the operation has been properly conducted this will take
place in the coure of ten or twelve hours. The contents of the vessel p should
then be transferred into another vessel, and the white lead being allowed to
subside, the liquor drawn off may, with a small addition of the solvent, be used
again to dissolve the oxide employed in future operations. The deposite of
white lead must now be washed in pure water, in order to remove the
remainder of the solvent, and when dried and prepared in the usual way will
be ready for the market. For the sake of economy, the material taken up
by the water in the first washing of the white lead may be concentrated by
evaporation, and introduced into the vessel p in any future operation. Instead
of the vessel p above described, I sometimes employ an apparatus represented
in section at Fig. 3, which is designed to be used when the oxide of lead to be
operated upon happens to contain insoluble impurities, as is commonly the
case with litharge and massicot. a, a, a, is a deep vessel of wood, and b, b, a
trunk, forming a narrow chamber contiguous to its side. c is a box
containing oxide of lead, which, on being introduced into the vessel a, rests
upon ledges near the bottom of the vessel, and these ledges are packed, to
prevent any liquid passing up the sides. This box has a perforated bottom and
also a perforated bed, and a filtering diaphragm of wash leather or other
suitable material is extended over and secured to the internal surface of each.
A long pipe d of lead or copper leads from the upper part of the vessel a into.

page_text: a cask e below, and a short pipe f from the same cask extends upwards
through the bottom of the vessel a, each of which pipes is furnished with a
stopcock. In the side of the vessel a an aperture is made, which is covered by
a flexible diaphragm g of wash leather or any other suitable porous substance,
the edges of the diaphragm being secured by a wooden frame in the inside of
the chamber. Into the vessel a is to be introduced a solution of acetate of
lead or acetic acid, and the cocks being opened in the pipes d and f, the
solution is allowed to fill the vessel a, the cask e, and the pipes d and f, to
within a few inches of the level of the lateral branch in the pipe d. A bent
pipe i communicating with the bottom of the trunk or chamber 6 leads into
upper part of the vessel a, and is furnished with a stopcock. A pipe k, which
is intended to be connected with the pipe v and the vessel u in Fig. 15, leads
into the upper part of the trunk or chamber 6, for the purpose of conducting
the gases into the chamber and through the diaphragm g into the vessel a.
The carbonic acid and other gases being forced by the pump r through the
air vessel u and pipe v, as before described in reference to Fig. 1, are
made to enter the chamber 6 by the pipe k, and the cock of the pipe i
being opened, any liquor which may have passed from the vessel a
through the diaphragm g into the chamber b, will by the pressure of the
gases be made to pass up the pipe i, and to discharge itself into the upper
part of the vessel a. The cock in the pipe i must now be closed, when the
gases filling the chamber band swelling the diaphragm g into the vessel a, will
by the force of the pump be passed through the pores of the diaphragm g,
and rise in a multitude of small bubbles thro' the solution. The effect of
thus introducing a quantity of gas into the solution in the upper part of the
vessel a will be to raise its column and cause the liquor to flow through the
lateral branch h, and the column of liquor in the upper part of the vessel a
thus becoming lighter, the liquor in the cask e and the lower part of the
vessel a will be forced upwards through the box c by the pressure of the
column in the pipe d. The solution or solvent being thus carried up through
the oxide in the box c, it will dissolve a portion of the oxide as it passes, and
this being acted upon by the carbonic acid gas which proceeds in bubbles
through the solution, will cause the white lead to be produced and carried
over by the continued current down the pipe d into the cask e, where it will
become deposited.
In employing those parts of the apparatus described above, in which
the oxide is dissolved and the white lead formed, it is not absolutely.
necessary to connect them with the furnace and vessel in which the lead.
is oxidised and the carbonic acid gas generated, as described in reference to.

page_text: Fig. 1; for if the lead were to be properly oxidised by any other suitable
process, and if carbonic acid gas were to be generated by any other means,
and the two substances be brought to act upon each other in the manner
described, a very important part of my object might be effected. I therefore
desire it to be understood that the particular features which I claim as my
Invention under the above recited Letters Patent are,-
First, the mode of heating metallic or blue lead by the combustion of
charcoal, in order to dispose it to take up or combine with the oxygen of
the atmosphere, which is drawn through the furnace, in connection with the
retention and application of the carbonic acid gas so generated to the purpose
of carbonating oxide of lead, as described above.
Second, the mode of operating upon oxide of lead for the purpose of
converting it into ceruse or white lead, as described above. And,
Third, the construction, arrangement, and adaptation of apparatus capable
of effecting those objects, as set out in the Drawing hereto annexed, as
described above.
Ip witness whereof, I, the said Thomas Robert Sewell, have hereunto
set my hand and seal this Tenth day of July One thousand eight