Improvements in the Manufacture of Metallic Oxides and in Apparatus therefor.
Year: 1888

page_text: Improvements in the Manufacture of Metallic Oxides and in
Apparatus therefor.
I, SYDNEY PITT, of Sutton, in the County of Surrey, Gentleman, (a communication
to me from abroad by Arthur Crossman Bradley, of Brooklyn, in the State of New
York, United States of America Gentleman) 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:-
The processes that have hitherto been employed to manufacture the metallic oxides
used as pigments and paints have been, so far as my knowledge extends in the case
of the oxide of lead known as litharge, to expose a mass of the molten metal in an
open hearth reverberatory furnace to the products of combustion of fuel mixed with
more or less air, accompanied with the stirring of the metal to expose fresh surfaces
to the action of such products; or to expose the lead in a hot revolving retort to air
and the products of combustion which are drawn through the retort, which is turned
during the operation to expose fresh surfaces of the lead to the action of the air. In
thelease of the white oxide of zinc, the process has been to volatilize the metal either
from a inolten mass of it, or from a mass of its ore sometimes mixed with fuel, and
permit the metallic vapour to burn in air. The process of manufacture by the first
process is tedious and requires the expenditure of much labour to stir the molten
metal and to free the oxide from the metal as it is formed; the second is also tedious
and requires the expenditure of power to turn the retort and the lead within it; the
product also in the first case is soiled with the earthy matter from the fuel. On the
other hand, the processes of manufacturing the oxide of zinc are either attended with
the mixture of earthy matter from the fuel with the product (which injures its value),
orjare slow and require a large expenditure of fuel to volatilize the metal from a mass
of it.
The object of the present invention is to enable metallic oxides to be produced with

page_text: far greater rapidity than by the previous processes of heating the lead in a large mass
or in a divided state in a revolving retort, and without a preliminary vaporizing of
the metal, and with a large saving of labour. In order that my invention may be
fully understood I will proceed to describe the mode in which I have worked with
success and the new apparatus which I have used for the purpose.
Figure 1 of the accompanying drawings represents a front view of an oxidizing
furnace which I have used with success.
Figure 2 represents a vertical central section of the furnace with some parts in
elevation.
Figure 3 represents a horizontal section of the furnace following the zig zag
lines X, X, of Figure 2.
Figure 4 represents a section of one of the hollow fire brick blocks of which the hot
air heating pipe is built up.
Figure 5 represents a vertical central section of a modified construction of oxydizing
furnace.
Figure 6 is a horizontal sectional view of the same.
The said furnace Figures 1 to 4 inclusive, consists substantially of two parts;
viz., an oxidizing chamber A, and an air heating apparatus B, both heated by means
of burning fuel. The oxidizing chamber A, has the form of a pipe which is sustained
in a furnace C, at the lower end of which there is a grate c, upon which the fuel is
burned. This chamber is provided above the grate with an opening or nozzle a, by
which it is connected with the heating apparatus B, for heating air; and the said
chamber is fitted at its upper end, or head a', with an escape pipe a², by which the
chamber is connected with a dust collector. At the upper end of the oxidizing chamber A,
there is a charger D, by means of which the inetal to be oxidized is fed to the
enclosed oxidizing chamber, and the neck of this charger is preferably fitted with a
sliding gate or valve d, by means of which the supply of metal can be regulated.
The neck d' of the charger is preferably extended into the oxidizing chamber sufficiently
to have the lower end of the neck below the orifice of the escape pipe a², and, as it is
desirable to prevent the metal when previously comminuted from inclting in the neck
of the charger, the extension of the neck into the said chamber is surrounded by a
water jacket d, through which a current of water is caused to pass; the water being
supplied by means of a water supply pipe e and the warm water being permitted to
escape through an escape water pipe e¹.
The air heating apparatus may be of the same construction as the pipe hot blast
ovens used in the manufacture of pig iron; but the air heating apparatus which I
have used with success consists of convoluted pipes b, formed of hollow fire brick
blocks that form two worm like passages, which are analogous to the two threads of
a double threaded screw, and which communicate at their lower ends, by means of
the connecting pipe 1, with the nozzle a of the oxidizing chamber. The upper ends
of the air passages are connected by means of a pipe E (a part only of which is
shown in the drawings) with an air forcing machine; that which I have used with
success being an ordinary Root Blower; and as the construction of air forcing
machines is well known in metallurgy, I do not deem it necessary to describe one in
detail. The convoluted pipe or pipes are sustained in a furnace F at the lower end
of which there is a gratef on which fuel is burned to heat the pipes and the current
of air which is forced through them by the air forcing machine, so that the air is
highly heated when it enters the oxydizing chamber.
The lower end of the oxydizing chamber is extended downward through the grate c
and through the ash pit cl of the furnace, and forms a receptacle a³ to receive any
unoxydised metal, which may be removed at intervals through an opening or doorway
provided for the purpose, said doorway being fitted with a door a*.
The escape pipe a of the oxydizing chamber is connected with a dust collector,
which may be of any suitable construction such as is used for collecting dust in the
useful arts. Thus, the said dust collector may be a large chamber fitted with partitions
forming a tortuous passage similar to the dust collectors used in collecting flour dust,
or with a series of wire cloth partitions. Or the dust collector may consist of a

page_text: series of pipes with bag attachments similar to those used for collecting the oxide of
zine; or, it may consist of a large chamber having such a bag collecting apparatus
connected with it, so that the said chamber may collect the first portions of the oxide,
and the bag collectors may collect the residue; but when bag collectors are used, the
current proceeding from the oxydizing chamber must be cooled sufficiently before it
reaches the bags by being caused to pass through long pipes or otherwise, to prevent
the bags from being burned by the heat. In all cases the dust collecting apparatus
should be fitted with openings, or doorways closed by doors, to enable the dust to be
readily removed. As the construction of dust collectors is well understood in
metallurgy, I do not deem it necessary to describe them in detail.
In order that my process may be fully practiced, it is essential that the metal to be
treated shall be in a comminuted condition before it is oxydized; by which I mean
that the metal to be oxydized shall be reduced to the condition of sand or minute
globules, as distinguished from the metal in mass on the one hand, and from metal in
the condition of vapor on the other. I prefer that the metal shall be comminuted
before it is fed into the oxydizing furnace, and the mode of comminuting the metal
which I prefer is to permit a stream of the molten metal to fall upon a rapidly
revolving disc, the practical effect of which is to throw off the metal by centrifugal
action in a powdery or sand like condition; and as this mode of comminuting
metal is well known in metallurgy, it is unnecessary to describe it in detail.
I prefer to heat the oxydizing chamber A to a temperature somewhat higher than
that at which the metal to be treated will burn in air, and the hot air apparatus should
be heated hot enough to heat the current of air which is forced through it to a
temperature at which the metal in a comminuted condition will burn in its passage
through the oxydizing chamber. When then the air forcing apparatus is in
operation, a current of highly heated air is forced through the oxydizing chamber.
The comminuted metal to be oxydized, which may be lead, is placed into the charger D,
and is permitted (by opening the gate d) to flow into the oxydizing chamber. The
comminuted metal falls through the said chamber in a shower, so that the atmosphere
therein has free access to its particles which are acted upon simultaneously by heat,
and the current of air; consequently the metal burns or oxydizes rapidly, and is
converted mainly into a pulverulent oxide. As the current of hot air, in which the
metal is burnt, is enclosed or confined by the walls of the oxydizing chamber, the
pulverulent oxide produced cannot escape from the current but is carried off by
the current and is deposited in the dust collector, whence it may be removed through
the doorways or openings provided for the purpose. If a bag dust collector be used,
its bags must be made of cloth pervious to air; so that the air will filter through the
cloth of the bags, leaving the oxide within them to be withdrawn at intervals as is
customary with this class of dust collectors. Such larger particles of the comminuted
metal as are not fully oxydized, drop into the receiver a³ at the lower end of the oxydizing
chamber, and may be removed at intervals through the doorway provided as above
described: Instead of connecting the upper orifices a² of the oxydizing chamber with
the dust collector, and the lower orifice a with the air heating apparatus, the upper
orifice a' may be connected with the air heating apparatus, and the lower. orifice a (or
the upper portion of the receiver a³) may be connected with the dust collector ;
and in such case the current of air will be downward through the oxydizing chamber.
When the metal that is treated is lead, the oxide produced as above described is
Litharge, and it is produced in such a finely divided condition that it is particularly
fitted for a pigment; moreover, as the oxydation is effected in a chamber from which
the earthy products of the combustion of mineral fuel are excluded, the oxide is. not
soiled by admixture with earthy matter.
The oxydizing chamber should be formed of a material that will withstand the heat,
the part which is in the furnace having been constructed by me of fire brick material;
and it should (if necessary) be lined or coated on its interior with some material that
will not melt readily when acted upon by the metallic oxide. When lead is the metal
that is oxydized, I have found that it is expedient to line the inside of the part of.the
oxydizing chamber which is within the furnace body with bone ashes, which may be

page_text: moistened and rammed in around a wooden former or core which is subsequently
withdrawn.
As before stated, the apparatus used for practising my said process may be varied;
thus for example, if natural gas or other heating gas can be had at a lower cost for
the purpose than coal, the oxydizing furnace above described may be heated with gas
instead of with coal by using gas burners of the usual construction instead of
grates or, the gas may be burned in the oxydizing chamber. A section of an
oxydizing furnace heated on the latter plan by natural gas is represented at
figure. In this case the oxydizing chamber A is fitted with burners c through
which natural gas is introduced; these gas burners being of the construction
of the well known Bunsen Burner, so that the gas is mixed with air. The action
of the Bunsen Burners introduces an excess of air and creates a strong draught
upward through the oxydizing chamber, and whatever additional air may be
required to thoroughly oxydize the metal is admitted through one or more orifices
beneath the gas burners; a forced current being introduced if a current strong enough
to make the operation practically successful is not obtained by draught. The gas burners
must be of sufficient capacity to heat the oxydizing chamber and the current of air passing
through the same to the requisite temperature for the rapid oxydation of the metal.
The pulverulent oxide produced in the gas furnace is carried out of the chamber with
the current of air, and is collected in the dust collector, as previously described with
reference to the oxydizing furnace first described in the Specification.
The improvements thus far described constitute the first division of the invention.
The second division of the invention has reference to the manufacture of those metallic
oxides, such as Orange Mineral and Red Lead or Minium, which contain a larger
amount of oxygen that can be combined with the metal by the hereinbefore described
process and means. In the manufacture of these oxides according to my invention,
the lead is first oxydized by the process and means previously described and is thereby
converted into Litharge, which is collected in the dust collector in the form of
pulverulent oxide or dust. The litharge obtained from the dust collector as herein-
before described in the first operation is then roasted in the same manner as is
practised in the production of Orange mineral from white lead, and of red lead from
the litharge produced by oxydizing a molten mass of lead; the pulverulent or dust
litharge obtained as previonsly described in this specification being stirred during the
roasting so as to expose it thoroughly to the action of air and effect its super-oxyda-
tion. As the construction and management of a reverberatory furnace for such purpose
is well understood in the art, it is not necessary to describe them.
The orange mineral and red lead obtained by said compound. process are not only
produced with a less expenditure of labor than has hitherto been required, but are
remarkably brilliant in color, which is believed to be due to the fact that the dust
litharge, which is produced in the first treatment from comminuted lead as herein
hefore described, is in an extremely divided condition, so that the super-oxydation is
more thorough than has hitherto been obtained.
•
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed 1 declare that what 1
claim is
1. The process substantially as before set forth of manufacturing an oxide of a
metal which consists in exposing the metal in a comminuted condition to the action
of an enclosed current of air heated to a temperature sufficient to burn the metal.
2. The process substantially as before set forth of manufacturing the oxide of a
metal, which consists first, in exposing the metal in a comminuted condition to an
enclosed current of air heated to a temperature sufficient to burn the metal; and
second, in collecting the dust oxide from said current.
3. The apparatus substantially as described in reference to figures 1 to 4 of the
drawings.
4. The apparatus substantially as described in reference to figures 5 and 6 of the
drawings.

page_text: 5. The compound process substantially as before set forth of manufacturing the
superoxide of a metal, which consists first, in subjecting the metal in a comminuted
condition to an enclosed current of air heated to a temperature sufficient to burn the
metal; and second, in roasting the pulverulent oxide collected from the first operation,
so as to super-oxydize the same.
6. The improvements in the manufacture of metallic oxides and in apparatus
therefor substantially as before set forth.