IMPROVEMENTS IN THE MANUFACTURE OF PROVISIONAL SPECIFICATION
Year: 1880

page_text: LETTERS PATENT to William Thompson, of Limehouse, in the County of
Middlesex, for an Invention of "IMPROVEMENTS IN THE MANUFACTURE OF
PROVISIONAL SPECIFICATION left by the said William Thompson at the
Office of the Commissioners of Patents on the 6th October 1880.
WILLIAM THOMPSON, of Limehouse, in the County of Middlesex. " IMPROVE-
MENTS IN THE MANUFACTURE OF WHITE LEAD, AND IN THE APPARATUS EMPLOYED
THEREFOR
The present Invention relates to improvements in the mode of preparing metallic
lead for manufacture, and for manufacturing white lead in enclosed spaces,
chambers, or rooms. In a former Patent of mine No. 4142, dated 7th November
1877, I set forth some novel and improved methods of preparing metallic lead for
after treatment, and in the after treatment of that lead in the course of converting
it into white lead. My present Invention consists in still further improvements
for effecting the same object (viz.):-The speedy conversion of metallic into white
lead.
I prepare metallic lead for manufacture into white lead by casting, stamping, .or
otherwise shaping lead so as to present as large a surface as possible to the action
of any chemical agent which I may employ.
It is of importance in making white lead that the surface of metallic lead to be
put under treatment should be quite clean and free from any grease or impurity,
which grease or impurity would in a great measure retard or altogether prevent
the process of its conversion into white lead.
To guard against any such impurities I wash the lead to be converted with acetic
acid and water before putting it into the converting chamber, or in place of acetic
acid and water I wash it with a solution of ammonia, and thus cleansed, the
metallic lead is introduced into the converting chamber, and the process of
chemical action at once proceeds and extends uniformly over the surface of the
metal. I introduce the metallic lead into a closed room or converting chamber
constructed of some material or materials which will not be attacked by the
chemicals, and which will not deteriorate the material manufactured.
The fittings, pipes, and taps which are required to conduct and to regulate the
supply of the gases and vapours are also made of such materials as are capable of
resisting the action of the gases and vapours, such as india-rubber, gutta percha,
tinned copper, tin, or pewter rich in tin.

page_text: It is understood I do not claim the use of these materials or any one of them, nor
do I confine myself to them; I make use of any convenient and suitable substance
for constructing and fitting my apparatus.
The gases employed for the conversion of the metallic to white lead are introduced
into the converting chamber by means of pipes, one or more of which may discharge
into gas chambers upon and connected with the top of the converting chamber, or
the pipes may be affixed to other parts if more convenient, as the gases and vapours
should be supplied so as not to produce violent currents, which are very injurious.
The supply pipes which enter the gas chamber terminate in glass globes, or vessels
of glass or other material, and these glass globes or vessels being heated to the
temperature of the converting chamber, serve as heaters to the entering current of
gas, which circulates inside the glass globes or vessels before entering the principal
space of the converting chamber.
Said chamber is provided with an inner roof made of glass, enamelled slate, or of
any other suitable material, inclined with the roof and a few inches therefrom for
the purpose of conducting away any condensed matters, and to prevent such
condensed matters falling in drops on the materials undergoing conversion within
the chamber. I sometimes make the inclined roof of the converting chamber of
non porous non absolvent material, and dispense with an inner roof, the condensed
matters being conducted away and caused to drop or fall clear of the materials
undergoing conversion. The converting chamber should be fitted with some means
of at all times ascertaining the temperature within it. I prefer to use thermometers,
which are fixed in any convenient manner and place for such a purpose; the
mercurial bulbs of said thermometers may project within the chambers, and the
stems and scales of degrees without, so that observation with regard to the tempera-
ture of the converting chamber or chambers may at all times be conveniently made.
The thermometer stems should be enclosed in a case to protect them from
accidental injury. The temperature which I have found most fitting for work is
from 80° Fahrenheit to 120° Fahrenheit. The temperature of the interior of the
converting chamber may be obtained and sustained by hot water pipes or by
means of hot air pipes, but I prefer to heat the chamber by ineans of steam pipes
which enter the converting chamber at one end, pass completely round it and out
again, and are connected with a steam service at one end, and with a waste service
at the other, said pipes being fitted with regulating taps or valves in the usual way.
The steam pipes are laid in a trough contained in or formed in the bottom of the
converting chamber, said trough containing acetic acid and water, which is supplied
as required in any convenient manner. The acetic acid and water covers or partly
covers the steam pipes in the trough containing it. When steam is passed through
the pipes, the liquid contents of the trough are evaporated into the converting
chamber. The contents of the converting chamber are then brought to and
sustained at any required temperature, and the atmosphere of the converting
chamber is at the same time kept charged with the necessary acetic acid vapours
to act upon the materials placed within. To give more command of the temperature
within the converting chamber and the evaporative energy employed, a smaller
additional steam pipe may be employed to act conjointly with the larger one, if it
is necessary to increase the temperature of the converting chamber; but more
generally the use of the smaller steam pipe is to continue and to sustain the
temperature and the evaporation of the acetic compound in the trough when the
larger pipes are out of use. When the temperature of the converting chamber has
been raised by the action of the larger pipe, and when the converting chamber is
sufficiently charged with acetic gas and vapour, the larger pipe may be dis-
engaged, and the smaller one made use of to sustain and continue the operation.
This heating and evaporating contrivance is situated generally beneath, that is,
immediately under the shelves, trays, or other supports holding the substance to be
converted; but more than one such apparatus may be used in the converting
chamber when desirable. For instance, the chamber might have two or more of
such heaters and evaporators, one under each truck or moveable framed support

page_text: employed to contain the substance undergoing treatment. When the chambers are
very large and the amount of material contained to be converted is large, I make
use of a series of troughs for containing acetic acid and water.
These troughs
The
are suspended from the shelves supporting the materials undergoing conversion
and contain acetic liquid, which by the beat of the chamber is kept in con-
tinual evaporation. These troughs are arranged so as to be fed or emptied from
the outside of the converting chamber as the operation proceeds, and more or
less acetic vapour is needed. I can employ my improved beating and evaporating
apparatus in place of the troughs for increasing the temperature or the evaporation
of acetic compounds in the converting chamber, or both. The heating and evapo-
rating apparatus is then an independent apparatus, and can be attached to or
detached from the shelves or other supports. It is fed with steam, and is supplied
with liquid in any convenient way. I may also employ if needed additional heating
apparatus in the converting chamber, such as hot air or steam pipes, in any suitable
way. The converting chamber may be fitted inside with shelves for holding the
material to be converted, or with shelves and trays, but I prefer to arrange so as to
be able to charge and discharge the converting chamber at one operation. This I
do by employing moveable trucks or framed supports made of any suitable material,
so constructed as to run on rails or tramways fitted inside and outside the chamber.
These trucks or framed supports constitute a series of shelves or supports for the
material to be converted, or supports for trays containing that material.
converting chambers are fitted with glazed doors and windows made to open and
close tightly to prevent any escape of gases or vapours. This permits the workman
to watch the progress which is being made and to observe the condition of things
within the converting chamber, by which observations the workman is able to
learn what is needed and to control the supply of the various chemical agents used
in the converting process. To the converting chamber I attach at some convenient
place, generally to the upper part of the gas space of the converting chamber, a waste
box with pipe and valve. This pipe communicates with the chimney or elsewhere,
and is used to conduct away any waste gases or vapours, and this under ordinary
circumstances is sufficient guard against the escape of any waste deleterious gases
or vapours into the factory. But it is sometimes necessary to absorb these deleterious
gases, as, for instance, when no furnace shaft exists to discharge them into; under
these conditions I arrange for the absorption of the waste deleterious gases or
vapours in an apparatus fitted to the gas space of the converting chamber; said
apparatus consisting of vessels or boxes of enamelled metal, wood, or other suitable
material; these vessels are fitted with an inlet pipe, by which they communicate
with the converting chamber; they are also fitted with an outlet pipe. The vessel
in one form is fitted with partitions reaching alternately from the inner top side
nearly to the bottom of the vessel and from the inner bottom side nearly to the top
of the vessel, so as to compel the waste gases and vapours passing through it to
pass in a circuitous passage from the converting chamber through the vessel which
I fill with coke or some porous substance which has been moistened with water or
water rendered alkaline by alkaline substances. The waste gases and vapours are
absorbed in their passage through the moistened porous material.
A tap is pro-
vided for drawing off any liquid which collects at the bottom of the vessel, and the
partitions attached to the bottom of the vessel are perforated to permit of the fluid
matter collected from the surface of the coke freely passing to said tap; the vessel
should also be provided with, man holes for emptying or recharging. Another mode
of accomplishing the absorption of the waste gases or vapours of the converting
chamber is by the use of water in the purifying vessel, the gases or vapours being
compelled by means of the partitions to pass over the surface of the water in. close
proximity thereto. A man hole and a glass guage for ascertaining the heighth of
the fluid contents of the vessel, together with means for filling and emptying, are
supplied in the usual course.
Having thus described the various portions of the apparatus I employ, I now
describe my improved process of converting metallic lead into white lead. The

page_text: converting chamber, whether fitted with shelves or containing my improved
moveable truck or other supports, having been charged with the lead to be con-
verted into white lead, the heater and acetic evaporation is charged with acetous
liquid, generally with acetic acid and water (in the proportion of one of acetic acid
to twenty of water, or thereabouts), the converting chamber is then closed; steam is
now passed through the pipe of the heater and evaporator to raise the temperature
of the converting chamber to from 80° to 120° Fahrenheit or thereabouts, and to
produce partial evaporation of the acetic compound contained in the evaporator.
When the temperature of the converting chamber has just been raised, atmospheric
air, preferably in a heated state, is passed into the converting chamber from any
convenient apparatus, generally from a gas holder, through one or more of the pipes
and globes or other vessels connected with the converting chamber as before described,
and the action of the current of air and of the acetic vapour and gases from the trough
is kept up for from 3 to 6 days and nights, according to the quantity of lead to be
operated on. During this period the metallic lead is attacked and becomes coated
with a whitish coating of hydrated sub oxide and hydrated subacetate of lead, a
mixture of these lead compounds being formed on the surface of the lead. The
process is continued, but now with the combined action of carbonic acid gas, which
gas is generated in any convenient and economical manner and purified in the
usual way, and is passed through one or more of the before described pipes and
globes or vessels, eventually finding its way to the interior of the converting
chamber to accomplish the work of carbonating the compounds of lead already
formed.
The combined action of the acetous compounds and vapours, atmospheric air, and
carbonic acid is kept up at a proper and regulated temperature increasingly for
Buch a time as is sufficient to convert the metallic lead into white lead. The time
necessary for the completion of the process of conversion depends on the thickness
of the metal submitted to the converting operation; from 12 to 28 days is sufficient
time, the longer period being required by lead which is half inch in thickness, and
the lesser time by that which is not so thick. When the process of conversion is
completed, the supply of steam and gases and vapours is turned off both from the
heater and evaporator and from the converting chamber. The atmospheric air and
carbonic acid gas may be warmed and brought to the same temperature as the
atmosphere within the converting chamber by any convenient means before entering
that chamber. It is found that the combined action of the gases and vapours is
more energetic when all are acting at the same temperature. When the conversion
of metallic lead into white lead is complete I allow the room or converting chamber
to cool and clear of any residual gases and vapours by either blowing air through
the room or converting chamber or by exhausting the air from the chamber at one
part and allowing air to enter at another. The room or converting chamber may
now be opened and the contents removed without any injury or even inconvenience
to those engaged. The white lead produced is washed, ground, and prepared for
the market in the usual manner. It is to be observed that in my improved process
of manufacturing white lead I not only produce a commercial article of absolute
purity, but one which cannot be excelled if equalled in density, in homogenity,
in opacity, in chemical composition, or in body power when made into a paint, and this
my improved process can be carried out on the largest or smallest scale, and that
absolutely without any injury to those engaged. I have before proposed to use
closed chambers for the manufacture of white lead and also carbonic acid gas, air,
and acetic vapours, and I would have it clearly understood that my present
Invention consists mainly of improvements on the Inventions previously made
by me.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said William Thompson in the Great Seal Patent Office on the 5th
April 1881.
WILLIAM THOMPSON, of Limehouse, in the County of Middlesex. " IMPROVE-
MENTS IN THE MANUFACTURE OF WHITE LEAD, AND IN THE APPARATUS EMPLOYED
THEREFOR."
The present Invention relates to improvements in the mode of manufacturing
white lead in air tight chambers, the object being to effect the conversion of
metallic or blue lead into white lead of the best quality, both in respect to its
colour and "body," in a speedy and economical manner. It is well known that
several processes are at present employed for the conversion of metallic lead into
white lead, and that in all these the same chemical elements are employed but with
very different results, both as respects the quality of the product and the cost of
its production. The common process of obtaining white lead is that in which the
metallic lead is subjected to the action of the heat and vapours arising from spent
tanners' bark and dilute acetic acid contained in vessels embedded in this bark.
The process of conversion is very slow, extending over from 3 (three) to 5 (five)
months, and when once started it is entirely beyond the control of the manu-
facturer. The percentage of corrosion moreover differs greatly from various causes,
and it is seldom if ever that the whole of the metal is converted. White lead
obtained by this method is liable to be discoloured by the tan vapours, and requires
to be carefully sorted (generally by hand labour) to remove the coloured portions
from the uncoloured portions. Attempts have been made from time to time to
avoid the defects inseparable from the tan stack process by the use of an air tight
converting chamber into which the chemical elements for corroding and converting
the lead could be introduced and their supply controlled at pleasure, and I have
myself under a Patent granted to me on November 7th, 1877, No. 4142, succeeded
to some extent in removing certain difficulties which attended the tan stack mode
of manufacture. By my present Invention however I have succeeded still further
in my object of producing white lead of the best quality, the process being com-
pletely under the control of the manufacturer and ensuring a larger yield than has
heretofore been obtained from a given weight of blue lead, and also the entire
conversion of the lead supplied to the converting chamber. In carrying out my
Invention I use a close converting chamber similar to that described in the Speci-
fication of my above mentioned Patent, and by preference wheel carriages or trucks
on which the metallic lead to be converted into white lead is packed. I also
employ open gutters or troughs in the floor of the chamber for receiving the dilute
acetic acid and steam pipes for vapourizing the liquid, as described in the Speci-
fication of my former Patent. In the admission however of the atmospheric air
and the carbonic acid gas to the chamber I make a material departure from my
said Patent, inasmuch as I provide for these being supplied to the chamber so as
to prevent the formation of currents and eddies, which I find retard the chemical
action of the gaseous elements thus admitted. I moreover provide for the air and
gas entering the chamber at a temperature which shall correspond with that of
the chamber, and I also provide increased facilities for controlling the heat of the
chamber and the vapourization of the dilute acetic acid. In the accompanying
Drawing Fig. 1 shows in transverse vertical section, and Fig. 2 in horizontal
or sectional plan an air tight converting chamber constructed, according to my
Patent of 1877, with an inner or supplementary roof and with ends that open for
admitting the laden truck or wheel carriage and for discharging it after the process
of conversion is complete, such chamber being also fitted with an arrangement of
supply pipes constituting a part of the present Invention. In these Figures A, A,

page_text: is the closed converting chamber constructed of any suitable material; B is a
suspended or false roof, made of glass or equivalent material, and intended to
receive and convey away the drops of condensed vapour falling from the roof,
which condensed vapour might otherwise fall upon and waste or discolour the
white lead produced. The chamber A extends upwards at its apex into a longi-
tudinal channel C which is intended to receive the pendant pipes D, by which the
air and carbonic acid gas are admitted to the chamber. Of these pipes there may
be any convenient number, say three, and they are each fitted with branches D¹
which lead off to opposite sides of the chamber A, and connect with horizontal
pipes D which are pierced with holes along their whole length. The pendent
pipes D are furnished with hollow globes or chambers D³ of glass or other material,
such as that used for the pipes and for the cocks with which the pipes are fitted,
it being essential, as is well known to white lead manufacturers, that the material
used for such purposes within the chamber should be such as will resist the action
of the acetic acid and other vapour. The object of the globes or chambers D³ is to
destroy all tendency which the air or gas may have to rush into the chamber in
direct currents, and also to present a heating surface to the air or gas prior to its
exit from the pipes into the chamber. E is the carriage formed with a series of
shelves, on which are placed skeleton frames E¹ for receiving the metallic or "blue"
lead that is to be converted into white lead. These frames E' have a tray for their
base to receive any droppings from the blue lead, and they are provided with
horizontal bars or rails upon which rest lugs that project laterally from the cast
metal plates of lead.
"
These plates (which may be cast either solid or in the form of net or lattice
work) I prefer to make of some eighth of an inch thick, but any other determinate
thickness of plate up to half an inch may be used if thought desirable. These
plates I insert in the frame transversely of the same, and about an inch apart,
increasing the space in proportion as the thickness of the plate is increased in
order to provide ample room for the swelling of the lead during the converting
process. The carriage E is mounted upon flanged wheels which run in grooves
formed in the floor of the chamber and are continued beyond the opposite ends
thereof. F, F, are troughs formed in the floor of the chamber and supplied with
dilute acetic acid from a well F¹. G, G, are steam pipes fitted in the troughs F
and serving to vapourize the dilute acid supplied to the troughs. G¹, G', are
other and larger steam pipes, which are intended to heat the chamber at the
commencement of the operation, and to supply dry heat from time to time when
the steam is cut off from the pipes G on the occurrence of too free an evolution of
acid vapours. In order that the attendant may readily ascertain the temperature
of the chamber, suitable thermometers are provided, as shown at H, H, Figures 3
and 4. This double system of supplying heat to the chamber offers great facilities
to the attendant, as he can regulate the heat of the chamber without unduly
increasing or diminishing the temperature of the chamber or the amount of
contained gas and vapours. For the purpose of increasing or diminishing the supply
of air or of carbonic acid gas to the chamber, cocks are provided for cutting off at
pleasure any one or more of the horizontal pierced pipes D2 which admit (as will be
hereafter more fully explained), first air to the chamber, and then air and carbonic
acid gas combined. I will now describe my improved process of converting
metallic lead into white lead. The converting chamber having been charged with
the lead to be converted into white lead, the same having been previously washed
over with acetic acid or ammonia to clean its surface, the troughs F are charged
with acetous liquid, generally with acetic acid and water (in the proportion of one
of acetic acid to twenty of water or thereabouts); the converting chamber is then
closed, steam is now passed through the pipes G and G¹ to raise the temperature of
the converting chamber to from 80° to 120° Fahrenheit or thereabouts, and to
commence the evaporation of the acetic compound contained in the troughs. When
this temperature has been reached in the converting chamber, atmospheric air
from any convenient apparatus, say, for example, a gas holder, is supplied at a

page_text: moderate pressure through the globes and pipes D, D1, D2, D³, to the chamber, and
diffused through the same with only a comparatively slight disturbance of the
imprisoned atmosphere. The action of the air and of the acetic acid vapour thus
supplied to the chamber I maintain without interruption for from 3 to 4 days and
nights. During this period the metallic lead is attacked and becomes covered with
a whitish coating of hydrated sub-oxide and hydrated sub-acetate of lead, a mixture
of these lead compounds being formed on the surface of the lead. The process I
now continue with the addition of carbonic acid gas, which gas may be generated
in any convenient and economical manner. When purified this gas is supplied to
the chamber at a moderate pressure through the system of pipes and globes D, D¹,
D2, D3, or any portion thereof (together with a further supply of air) to accomplish
the work of carbonating the compounds of lead already formed, and this supply of
mixed gas and atmospheric air I maintain, until by inspection through suitably
arranged sight holes, I ascertain that the conversion is completed or carried to the
desired extent.
The proportions of atmospheric air and carbonic acid gas admitted simultaneously
through the same system of pipes to the chamber will be about equal in quantity.
The combined action of the acetous vapours, atmospheric air, and carbonic acid is
kept up at a proper and regulated temperature (by preference slowly increasing
from 80° until the maximum temperature of 120° Fahrenheit is reached) for such
a time as is sufficient to convert the metallic lead into white lead. The time
necessary for the completion of the process of conversion will vary from 12 to 28
days, according to the quality and the thickness of the lead. With good soft lead.
of an inch in thickness 12 days will usually suffice, and for the same lead an
inch in thickness 28 days will be sufficient time. I have found in practice that there
are certain conditions of the metal while under conversion that favour the process,
but there are others that do not. For instance, lead 1/8 of an inch in thickness
when treated with carbonic acid, acetic acid vapour, and air, after the formation
of the hydrated sub-oxide and sub-acetate becomes penetrated in parts, and the
coating of white lead falls off almost as soon as it is formed. With thicker metal
the white lead when formed on the surface of the blue lead exfoliates from the
surface of the metal, but does not fall away, it remains as a porous coating,
surrounding and partly attached to the remaining metallic core by its presence,
greatly favouring the action of the process of conversion of the remaining metal,
so that 28 days will suffice for this thickness. But in some cases, as when the
coating of converted lead from any cause, such as employing too great heat, gets
hardened and loses to some extent its porosity, it then protects the core of lead
from the action of the gases and vapours, and a longer time will be necessary for
the complete conversion of the metal. Again, when too much acetic acid and too
small an amount of carbonic acid is supplied to the chamber the coating is then
to some extent soluble in the vapours, and running over the lead coats and protects
it from proper continuous action. When the process of conversion is completed
the steam heat is turned off from the converting chamber, and the continuous supply
of air and carbonic acid gas is also stopped. The apparatus employed in carrying out
the above described process may be modified to suit the varied requirements of the
manufacturer. Figure 3 shows in cross section a chamber suited to receive two
carriages charged with cast plates of lead, the two loads being simultaneously
submitted to the process.
In this form of chamber no inner or supplementary
roof is required, the condensed vapours running down the inclines of the roof to
the centre, and falling into a gutter in the floor (between the carriages) provided
to receive the droppings. The arrangement of the pipes and troughs will be sub-
stantially the same as in the first described arrangement. Fig. 4 is a cross
section, and Fig. 5 a plan view of a chamber furnished with a modified arrange-
ment of distributing pipes. In this example the chamber has a door only at one
end for the admission and withdrawal of the carriage or truck, and the heating
pipe G is arranged so as to extend along the two sides and ends of the chamber,
it being necessary to dip the heating pipe at the entrance end of the chamber to

page_text: keep it clear of the carriage way. The distributing pipes instead of being within
the chamber, as shown at Fig. 1, are set outside the chamber, and have jets or
branches which enter the chamber at three different levels, and are furnished
with globes D³ which serve to heat the air or gas admitted to them, and to diffuse
the same gently throughout the chamber. In all the arrangements of distributing
pipes the cocks which control the delivery of the air and gas to the converting
chamber are made accessible to the attendant outside the chamber, as is clearly
shown in the Figures. The atmospheric air and carbonic acid gas may, if thought
desirable, be warmed and brought to the same temperature as the atmosphere
within the converting chamber by any convenient means before admission to the
distributing pipes, and this will be found desirable when the arrangement described
with reference to Figures 1 and 2 is employed. It is found that the combined
action of the gases and vapours is more energetic when all are acting at the same
temperature. When the conversion of the metallic lead into white lead is complete
I cool the converting chamber and clear it of any residual gases and vapours, either
by blowing air through the converting chamber or by exhausting the air from the
chamber at one part, and allowing air to enter at another. The converting chamber
may then be opened and the contents removed without any injury or even
inconvenience to those engaged in the manufacture. The white lead produced is then
prepared for the market in the usual manner. It is to be observed that in my improved
process of manufacturing white lead, I not only produce a commercial article of
absolute purity, but one which cannot be excelled, if equalled, in density, in
homogenity, in opacity or body power, when made into a paint, and this, my
improved process can be carried out on the largest or smallest scale, and that
absolutely without any injury to those engaged in the manufacture. To the con-
verting chamber I attach at some convenient place, generally to the upper part of
the gas space of the converting chamber, a waste box, fitted according to the
Specification of my above-named Patent. A pipe from this box communicates with
an adjacent chimney, and is used to conduct away any waste gases or vapours.
This, under ordinary circumstances, is sufficient guard against the gases or vapours
passing into the factory; but it is sometimes necessary to absorb these deleterious
gases, as, for instance, when no furnace shaft is available for receiving them. Under
these conditions I arrange for the absorption of the waste deleterious gases or
vapours, in an apparatus arranged as shown in the sectional view Figure 6, and
connected with the converting chamber. This apparatus consists of a vessel or box
of enamelled metal or of wood or other suitable material, fitted with an inlet pipe,
by which it communicates with the converting chamber, and also with an outlet
pipe. The vessel in one form is provided with partitions reaching alternately
from the inner top face nearly to the bottom, and from the inner. bottom face
nearly to the top, by which means the waste gases and vapours passing through it
are compelled to travel in a circuitous passage from the converting chamber
through the vessel, which I fill with coke or some porous substance which has been
moistened with water, or water rendered alkaline. On exhausting this vessel the
waste gases and vapours will be drawn into the box and absorbed in their passage
through the moistened porous material. A tap is provided for drawing off any
liquid which collects at the bottom of the vessel, and the partitions attached to the
bottom of the vessel are perforated to permit of the fluid matter collected from the
surface of the coke freely passing to the tap. The vessel should be also provided
with manholes in each compartment for charging or emptying the vessel.
modification of this mode of absorbing the waste gases or vapours of the converting
chamber consists in the use of water in the condensing vessel, the gases or vapours
being compelled by means of the partitions to pass over the surface of the water in
close proximity thereto. The apparatus employed in this case is illustrated in the
'sectional view Fig. 7, a manhole and a glass guage (for ascertaining the height
of the fluid contents of the vessel being provided together with means for filling
and emptying the vessel.
A
Having now set forth the nature of my Invention of improvements in the

page_text: manufacture of white lead and in the apparatus employed therefor, and having
explained the manner of carrying the same into effect, I would have it understood
that I do not claim generally the admission of a regulated supply of air and
carbonic acid gas to a confined atmosphere of acetic acid vapour, in which metallic
lead is exposed to corrosion, but what I claim as my Invention and desire to secure
under the above in part recited Letters Patent is,―
First. The process of converting metallic or blue lead" into white lead, as
above described, that is to say, submitting metallic lead in a closed chamber to the
combined action of acetic acid vapour and atmospheric air in a temperature
ranging from 80° to 120° Fahrenheit, or thereabouts, for one sixth to one fourth of
the time required for completing the conversion of the lead, and subsequently
supplying to the closed chamber in addition to the acetic acid vapour, carbonic
acid gas and atmospheric air, and maintaining the supply until the conversion is
completed, the admission of the air and gas being so controlled as to provide for
their diffusion through the chamber without the creation of disturbing currents.
Second. The arrangements of apparatus above described for supplying atmos-
pheric air and carbonic acid gas to the converting chamber, and diffusing the
same through the chamber in a heated state.
Third. The means above described for clearing the converting chamber of gas
and vapours and condensing the same preparatory to opening the chamber for the
removal of the white lead.
In witness whereof, I, the said William Thompson, have hereunto set my
hand and seal, this Second day of April, in the year of our Lord. 1881.
25 Witness,
PHILIP M. JUSTICE,
14, Southampton Buildings,
Chancery Lane,
Patent Agent.
WM. THOMPSON. (L.S.)