Improvements in the Manufacture of Plumbic Oxide or Litharge and in Apparatus Employed therein.
Year: 1887

page_text: Improvements in the Manufacture of Plumbic Oxide or Litharge and
in Apparatus Employed therein.
We SAMUEL CONSTANT ROWELL of Boston in the State of Massachusetts one of
the United States of America Dealer in Machinery and JAMES WEBSTER NEWELL of
Boston aforesaid Iron Merchant do hereby declare the nature of this invention and in
what manner the same is to be performed, to be particularly described and ascertained
in and by the following statement :-
This invention has for its object to provide a method whereby plumbic oxide, or as
it is commercially known litharge, may be produced from metallic lead more quickly
and in a purer state than has heretofore been accomplished.
We have by experiment discovered that litharge of purer quality may be rapidly
and economically produced by placing the lead in a retorting furnace or chamber the
outside of which is heated to the required degree, the retorting chamber being
supplied by air preferably heated and preferably supplied at the bottom of the said
chamber, or in such manner as to pass upward through and over the molten lead, thus
keeping the said lead in agitation, the preferably heated air forced into the said chamber
thus agitating the lead, which results in exposing to the oxygen of the heated air a
greater surface of lead than otherwise thus more thoroughly and rapidly oxydizing
the lead.
In the practice of our invention we prefer to divide the process into two steps i.e.
first, heating the metallic lead in a retorting chamber to or a little above its melting
point, and when raised to such heat forcing preferably heated atmospheric air over or
through the molten mass of metal, whereby the lead is converted into impure litharge,
the impurity of the litharge consisting chiefly of metallic lead, the impure litharge
appearing in the form of a dross, which, removed from the retorting chamber, is
secondly submitted in a calcining chamber, maintained at a heat preferably higher than
that at which the retorting chamber is maintained, to the influence of air, preferably
more highly heated than the air in the retorting chamber in which the lead was first
placed.
Our invention consists in a furnace having certain novelties of construction as will
be hereinafter described; and also in a new method of forming litharge.
Figure 1 is a vertical section of a furnace with which to practise our invention, the

page_text: section being taken on the irregular line x-x Figure 3 and also showing the chimney
in section.
Figure 2 is a transverse section of Figure 1 on line x-x¹.
Figure 3 a transverse section of Figure 1 on line y-y with the chimney removed, and
Figure 4 a side elevation of Figure 1 partially broken out to show the hot air
tuyere.
Referring to the drawings, A represents the brick-work of a furnace provided with a
chimney or flue A', herein shown as extended to the bottom of said furnace.
The interior of the furnace referred to is divided centrally by a wall a supporting
one end of the arched roof a¹ of a combustion chamber a³, containing the fire grate a
upon which is placed fuel, preferably coke, which furnishes the heat to melt the lead,
said beat being directed through said furnace in a manner to be hereinafter fully
described and designated by full arrows.
The central wall a also supports one end of the arched roof a forming part of a
flue c².
The brick-work as, suitably laid, forms the bottom of a calcining chamber a³ and
also the roof of a recoiving chamber a', said chambers being connected by a shoot or
passage as preferably located near one end of said chambers, as shown in Figure 3.
Above the arched roofs a, a, referred to and which constitute the top of the greater
part of the furnace, see Figure 4, the walls of the furnace are extended upward to form
the main or retorting chamber b.
The bottom of the retorting chamber b is herein shown as composed of a metal plate b
supported in the side walls of the furnace, said plate being preferably inclined and
concaved at one end as shown in the drawings to form a pan to receive and hold the
metal lead. The concaved portion of the plate & is herein shown as separated or divided
to leave a passage b', as shown in Figure 1.
The tuyere is herein shown as an integral part of the plate 61, the tuyere
communicating with the passage 3 by port . The plate ³, preferably of metal,
constitutes the roof of the calcining chamber a³ and also the floor or under part of the
flue c².
The upper portion of the plate 61 and upon which the lead is placed, is herein shown
as provided with perforations c, for the passage of air which is forced up through the
molten lead, said lead being melted by heat which escapes from the fire chamber a²,
through passage c¹, the flue c², thence through the flue passages c, c³, as indicated by
the full line arrows,
the latter passage being between the arched roofs a', a', and the
plate 6', and thence through the passage c into the chimney or flue A¹.
The air by which the molten lead is oxidized is preferably forced by an air pump,
not shown, through a series of connected pipes located in the fire chamber a and
shown in plan view Figure 3, the said pipes being herein shown as of arch-shape and
erected upon and communicating with boxes d', d, having partitions at suitable intervals
to compel the air entering the boxes to traverse the arched pipes, one after the other,
after the manner of a coil.
The boxes d', d, are supported upon the brick-work, as shown in Figures 1 and 3,
and extend throughout the length of the chamber a².
The boxes referred to and their attached arched pipes are so divided at or near the
centre of the length of the chamber a² as to form two batteries, one of which, as
hereinafter described, is made to receive atmospheric air and supply it in more or less
heated condition to the retorting chamber b, the other battery furnishing air more or
less heated to the calcining chamber a, the direction of flow of the heated air being
designated by the dotted arrows 2 and 3, the arrow 2 showing the course of the air
which enters the chamber b, and the arrow 3 that which enters the chamber a³.
The pipe which connects one of the said batteries with the tuyere is shown
partially in dotted lines in Figures 1 and 2, and completely in full and dotted lines
Figure 4.
From the tuyere & the heated air passes through the port 66, passage b², and
perforations c up through the molten lead, said lead being oxidized by said air chiefly
to litharge (Pho)

page_text: The litharge being of less specific gravity than metallic lead, rises to the surface of
the molten mass.
As the litharge is formed, it is raked or scraped up on to the inclined part of the
plate b, and when a sufficient quantity has thus been accumulated, a cover g of a shoot
or hopper g extended through the arch at and leading into the calcining chamber a³,
see dotted lines Figure 1 is raised, and the litharge and its impurities chiefly metallic
lead, are raked into the hopper or shoot g', through which it falls into the chamber a,
the metallic lead being acquired by the scraping of the litharge upon the inclined
plate 6.
Access to the chamber 6 is obtained through a door & in the side of the furnace.
The litharge and its impurities in the calcining chamber a are still further subjected
to the oxidizing influence of heated air, the cover g being replaced upon the shoot g'.
The heated air which passes through the calcining chamber a³ is forced therein from
the battery through a compartment in the box d², which compartment is connected
by pipe, see Figure 1, with a box or channel h°, said channel extending the length
of the chamber a, and being provided with a series of ports or openings ², see
Figures 1 and 3, which are connected with the calcining chamber as, the air being
forced into the battery from the front side of the furnace as indicated by arrow 3,
preferably by a fan, not shown.
The temperature of the calcining chamber will preferably be somewhat higher than
that of the retorting chamber b, it being preferably between the fusing and volatilizing
points of lead.
The excess of heated air in the calcining chamber a' finds an exit therefrom through
the passages k made at intervals in the wall of the furnace and throughout the length
of said chamber, said passages being made continuous and preferably connected to the
flue c².
From the flue c² the hot air passes through the passages c¹ and c and thence to the
chimney A¹ by the passage e, the hot air on its way to the chimney imparting heat
to the metal plate & thus assisting to the melting of the lead supported in the concaved
portion of said plate.
The products of combustion passing from the combustion chamber a through the
flue passage c, and into the chamber c, heat the metal shield c³, which radiates its
heat into the chamber að and down upon the litharge, thereby raising the temperature
of said chamber.
The impurities of the metallic lead which may be volatilized, and the excess of air
in the chamber b, are carried off by the flue m.
The litharge is permitted to remain in the chamber a until it has acquired the
desired color or tone, when it is scraped or raked through the shoot a into the
receiving chamber a', from whence it is taken ready for grinding.
Instead of dividing the plate b¹ and perforating the upper portion of said plate, we
may employ a false bottom which would rest upon the plate and would be provided
with perforations, the false bottom forming part of the tuyere 6º.
It will be herein noticed that the products of combustion are prevented from
coming in contact with the metallic lead, thereby preventing the formation of
comparatively large quantities of carbonate of lead which is formed when the products
of combustion come in contact with the lead and which exists as an impurity in
litharge thus made.
We have herein shown a mechanism well adapted to economically heat air and
introduce it into the retorting and calcining chambers, and we have also as so far
described referred to the form of heat as coal or coke upon the grate, but we wish it
to be understood that we do not desire to limit our invention to the employment of
the exact means herein shown for heating the air to be discharged into the said
chambers for instead thereof we may employ any usual means or method of heating
air to be introduced into furnaces for industrial uses and so also we may use as the
generator of heat, gas, oil, or any other usual fuel instead of coke, the use of gas or
oil as the fuel necessitating the application to the furnace of usual means for burning
the same.

page_text: Having now particularly described and ascertained the nature of our said
invention, and in what manner the same is to be performed, we declare that what we
claim is :-
1. In a furnace for the manufacture of litharge, the combustion chamber, the
retorting chamber to contain metallic lead and having a hollow bottom perforated to
permit heated air to be forced up through the lead, and passages connecting said
combustion chamber with the chimney and made to cause the products of combustion
to pass beneath and in contact with the bottom of the retorting chamber to melt the
lead, combined with a battery of pipes communicating with the retorting chamber
below its perforated bottom, substantially as 'described.
2. The combustion chamber, the retorting chamber, and a battery of pipes through
which heated air may be forced into the retorting chamber combined with a calcining
chamber located below and communicating with the retorting chamber, and with
a battery of pipes communicating with the calcining chamber to operate, substantially
as described.
3. That improvement in the process of manufacturing litharge from metallic lead,
which consists first in forcing air through the mass of lead in a molten state in one
chamber and second, in transferring the impure litharge thus formed to a second
chamber, and therein subjecting said impure litharge to the action of heated air in
said second chamber, substantially as described.
4. The improvement in the art or method of manufacturing litharge, which consists
in subjecting melted lead to the action of heated air in a retorting chamber, and
thereafter subjecting the dross or impure litharge thus formed to the action of heated
air in a calcining chamber, maintained at a higher temperature than the retorting
chamber, substantially as described.
5. That improvement in the art or method of manufacturing litharge from metallic
lead, which consists in forcing air heated to one temperature through the mass of lead
in a molten state to form a dross or impure litharge, and thereafter subjecting the
said dross or impure litharge to the action of air heated to a higher temperature to
impart to the said impure litharge the desired tone or color, substantially as
described.
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