IMPROVE- MENTS IN THE MANUFACTURE OF ZINC WHITE
Year: 1863

page_text: PROVISIONAL SPECIFICATION left by Michael Henry at the Office of
the Commissioners of Patents, with his Petition, on the 3rd November
1863. A communication from abroad by Alphonse Pallu, of 33,
Boulevard Saint Martin, Paris, France.
I, MICHAEL HENRY, of 84, Fleet Street, in the City of London, Patent
Agent, do hereby declare the nature of the said Invention for "IMPROVE-
MENTS IN THE MANUFACTURE OF ZINC WHITE," communicated to me from
abroad by Alphonse Pallu, of 33, Boulevard Saint Martin, Paris, France, to
be as follows:-.
Hitherto zinc of a certain description only has been considered available for
producing zinc white, whereas by these improvements zinc of other descrip-
tions or sources is rendered suitable for the same. Heretofore the usual
mode of manufacture has been to distil zinc in close retorts or crucibles
heated externally, the metallic vapours evolved being burnt by currents
of air.
Now, this Invention consists in the employment of combustible gases or
gaseous matters in and for the purpose of obtaining oxyde of zinc or zinc white,
whereby a much higher temperature is produced at the period of oxydation

page_text: than in ordinary methods; the gas preferred for the purpose is carbonic
oxyde. I proceed to describe certain methods of carrying this into effect. In
the three first the zinc is placed in a retort or crucible.
According to one method, combustible gas raised to a bigh temperature is
admitted into the retort, muffle, or crucible containing the melted zinc, and will
assist to carry off the metallic vapours, and thereby accelerate evaporation.
As the gas and metallic vapours are passing away from the retort, say, for
example, when they reach the beak or other convenient part, they are met by
currents of hot air which effect their combustion, and at the high temperature
evolved the oxyde will be produced.
In a second method combustible gas is admitted into the retort, and a
portion of such gas is burnt therein by air introduced through a separate
opening (in small quantities to prevent premature oxydation). The gaseous
currents are so regulated as to leave some of the gases unburnt; the gas and
air are heated before entering the retort, which may be done by passing them
between bricks made red hot by the spare furnace heat. The gas should,
preferably, be admitted about the level of the melted metal to keep it in a
reducing atmosphere and the air higher up. As the zinc vapours and the
excess of (or unburnt) gases are passing away from the retort they meet with
additional currents of air, and are burnt as in the first method.
According to a third method combustible gas and air are not conducted
into the body of the retort or crucible, but, having been previously heated,
they are brought into contact with the metallic vapours as these are passing
away from the retort; this may be done by admitting the gas and air into
the retort beak.
According to a fourth method the zinc is placed in a reverberatory furnace
instead of in a retort; into this furnace combustible gases are admitted, and
the zinc is thus subjected to the heat evolved by the combustion of its vapours
and of the gases. Premature oxydation may be prevented by introducing the
gases over the body of melted metal and the air at a higher point. While
distillation is being carried on, communication between the interior of the
furnace and the outer air is closed except through the chimney. As the
products of distillation and combustion travel to the chimney they pass through
chambers in which the zinc white is separated and deposited, the more volatile
products escaping. If the first oxydes evolved in the various methods should
be of bad color, they may be received in a chamber separate from that
intended for the subsequent or marketable products, and bleached by re-
heating them in a retort, crucible, or reverberatory furnace, or by subjecting

page_text: them in a close vessel to a current of carbonic acid and steam under pressure.
Instead of employing oxyde of carbon or like gases, air may sometimes be
used at a temperature higher than what it attains in a close vessel, as, for
instance, at the temperature at which it issues from Siemens' regenerating
furnaces.