Iм- PROVEMENTS IN THE MANUFACTURE OF WHITE LEAD, AND APPARATUS THEREFOR
Year: 1872

page_text: PROVISIONAL SPECIFICATION left by William Thompson at the
Office of the Commissioners of Patents, with his Petition, on the
29th October 1872..
I, WILLIAM THOMPSON, of No. 101, Wandsworth Road, in the County
of Surrey, do hereby declare the nature of the said Invention for "Iм-
PROVEMENTS IN THE MANUFACTURE OF WHITE LEAD, AND APPARATUS THEREFOR,'
to be as follows:-
"
In preparing white lead it is of great importance that the blue lead
acted on should be as pure as possible, and free from dross or other
matter which can float on the surface of the molten metal; also that
the fluid lead should be drawn off at a regulated temperature.
One part of this Invention relates to the construction and use of
melting apparatus, whereby the purity of the metal to be operated on
can be secured and its temperature can be regulated.
For this purpose
I construct a melting pan with three compartments separated from each
other by vertical partitions. One of these compartments is used for
melting the lead. From another of the compartments which com-
municates by an opening at its bottom with the melting chamber
the fluid lead is taken, and being thus supplied from the bottom of

page_text: the melting chamber it is free from dross or scum. The third com-
partment is kept cooler than the melting chamber, being arranged so
as to be farther from the furnace heat, and being supplied as required
with the lead to be melted. It communicates with the melting chamber
by a passage governed by a sluice or valve. Whenever the lead in the
melting chamber becomes overheated, a portion of the cooler fluid could
be run into it from the third chamber, and thus the temperature may
be regulated before any lead is withdrawn. Instead of one compartment,
as last described, there may be two or more containing metal at different
temperatures and serving as reserve chambers for the supply of the
melting chamber..
Lead is more readily acted on when a large surface of it is exposed,
and when it is of a comparatively loose texture. Another part of
my Invention relates to its preparation in such a condition. For this
purpose I provide a cylinder open at the end, and having a lip pro-
jecting inwards at each end. I mount this cylinder on rollers and
cause it to revolve thereon, and I pour the fluid lead into it. By the
rotation of the cylinder the lead is spread in a thin sheet of open
texture over its interior periphery, which sheet can be cut longitudinally
and removed and flattened. To facilitate its removal the lip at one end
of the cylinder may be made moveable. In order the more quickly to
cool the lead during this operation, I make the cylinder with a casing
supplied with cold water; or I cause the cylinder to revolve with the
lower part of its periphery immersed in a trough of water; or I pour
water over its exterior periphery, and in order to keep it moistened I
prefer to coat it with felt or other fibrous or spongy material. In order
to granulate the lead I mount a roller in bearings, and cause it to
revolve with a sloping knife adjusted near to its circumference. I pour
the melted lead into the angular space above the knife, whence it issues
in a thin stream through the passage between the edge of the knife and
the cylinder, and drops into water below, wherein it sets in granules.
The cylinder above described, by which the lead is made into sheets,
may be also used as the roller for granulation.
In the manufacture of white lead, the blue lead in sheets or granules
or other forms is acted on by acids and vapours in closed chambers
maintained at suitable temperatures. In charging and discharging these
chambers much time is usually lost, and there is a considerable waste
of the gases and vapours employed as reagents, and also a waste of heat,

page_text: because the chambers must to a great extent be cleared and cooled
before workmen can enter them.
Another part of my Invention relates to mean's for avoiding such loss
and waste. For this purpose I construct chambers with doors at each
end and lines of rails through them, and I provide trucks to run on
these rails. Outside the chamber I load a truck with the blue lead,
preferably arranging it in alternate layers of the thin sheets, and the
granules supported upon open trays or gratings. I then open one of
the doors of the chamber and run in the truck. When the lead has
been sufficiently acted on I open the opposite door of the chamber
and withdraw the truck. For continuous working both doors may
be opened at the same time, and a truck charged with blue lead
may be pushed in so as to push out the truck of lead that has been
operated on, and to take its place in the chamber. It is to be understood
that the chambers and trucks are formed wholly or principally of
materials such as slate, earthenware, glass, or the like substances that
are not acted on by the reagents used for acting on the lead; also that
the gases and vapours are supplied to the chambers preferably at their
lower parts, and that to ensure a circulation through the chambers,
fans or other mechanical propellers may be employed made of materials
not acted on by the reagents.