Improvements in the Manufacture of White Lead and in Apparatus therefor.
Year: 1892

page_text: Date claimed for Patent under Sect. 103 of Act,
being date of first Foreign Application (in 1st Oct., 1891
France)
Date of Application (in United Kingdom), 17th Mar.. 1892
Complete Specification Left, 17th Mar., 1892-Accepted, 30th Apr., 1892
COMPLETE SPECIFICATION.
Improvements in the Manufacture of White Lead and in Apparatus
therefor.
I JOHN WILLIAM HENRY JAMES of 4 Victoria Mansions Westminster,
Engineer 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 :-
My invention has for its object, to produce white lead of superior quality to that
at present produced, to economically obtain carbonic acid gas in suitable form for
use in the manufacture and to provide efficient apparatus.
The substances employed in the manufacture are mainly oxide of lead, acetic acid,
and carbonic acid gas, with moisture, heat, agitation and pressure.
First. To obtain with rapidity and certainty a mixture of about 65% of amorphous
carbonate of lead and 35% of hydrate of lead from oxide of lead. I proceed as
follows:-I mix one part of pure finely ground yellow litharge or oxide of lead
with from one and a half to two parts by weight of water (more may be used but
without advantage) and with from one tenth of one per cent. to one per cent. by
weight of acetic acid estimated as glacial. I agitate from the bottom upwards the
magma so produced and during the agitation I inject carbonic acid gas amongst it.
The injection and agitation are effected under pressure or not, at a temperature of
from 170° F. to 210° F. and are continued for from one to two hours until white
lead of the above composition is obtained.
Lead residues may be converted into oxides for use in the above process.
Second. The white lead mixture obtained as above set forth together with the
mother liquor or with the addition of water is slowly agitated in a horizontal
gyratory direction until the coarser particles settle, the supernatant liquor con-
taining the mixed and finely divided carbonate and hydrate of lead is then separated
from the said coarser particles, is neutralized, is filtered, and is afterwards dried at
a temperature of about 190° F. to 210° F. If the white lead mixture is discoloured
with sulphuretted hydrogen it is whitened by the addition of peroxide of hydrogen,
chlorine or like oxidizing agent.
Third. When dilute carbonic acid gas such as that obtained from a lime kiln
containing from 25% to 33% of carbonic acid gas, or that obtained by burning coal
or coke with excess of air, is used; the said gas is intimately mixed with sufficient
chlorine gas to decompose any contained sulphuretted hydrogen. The chlorine gas
is added before or during the passage of the said dilute carbonic acid gas through
a scrubber, so that any excess of chlorine is washed out and the sulphur is
deposited.
Fourth. When undiluted carbonic acid gas is to be used, I compress in the
presence of water carbonic acid gas diluted with nitrogen until the carbonic acid
gas is dissolved.
The aqueous solution of carbonic acid gas is separated from the nitrogen and is
relieved from pressure so that undiluted carbonic acid gas is evolved for use. The

page_text: expanding gas is used to cool the compressed gas and to produce motive power.
The water in which the carbonic acid gas is to be dissolved, contains the metallic
oxide such as oxide of iron or an oxidizing substance for absorbing or decomposing
sulphuretted hydrogen.
Fifth. Apparatus for carbonating consists of a horizontal cylinder of copper,
wood, or other material capable of withstanding corrosion, and is fitted internally
with rotating beaters carried on a solid or perforated hollow spindle passing hori-
zontally through bearings in the said cylinder. A trough is fixed externally from
end to end of the lower side of the cylinder and perforations pass from the said
trough to the interior of the cylinder at such an angle that the carbonic acid
enters the cylinder and flows in the same direction as the revolving magma.
pump is used to force the gas into the cylinder. Instead of one vessel, a series
of vessels may be used. The said carbonating cylinders are provided with charging
hoppers, discharge ways, thermometer sampling cocks and water and steam ways.
Steam is injected through the trough perforations or through the hollow perforated
spindle.
A
Sixth. Filter presses and hydro-extractors for use in separating water from white
lead are made of iron covered with sheet lead, or like material capable of
withstanding corrosion and pressure, and drying chambers are constructed with
superposed endless bands travelling in opposite directions so that the white lead
being dried, falls from band to band. The bands are constructed in any usual or
suitable way and kept stretched by any suitable or usual means, and deflectors are
used to cause hot air preferably heated by means of steam to the temperature
named to fully traverse the drying chamber.
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed, I declare that what I
claim :-
First. Treating a mixture of oxide of lead, acetic acid and water with carbonic
acid gas, for the production of white lead substantially as set forth under the first
head.
Second. Treating white lead so as to separate the finer from the coarser particles,
and when necessary decolourizing white lead, substantially as set forth under the
second head.
Third. Separating sulphuretted hydrogen from dilute carbonic acid gas substan-
tially as set forth under the third head.
Fourth. Separating nitrogen and sulphuretted hydrogen from dilute carbonic
acid gas, substantially as set forth under the fourth head.
Fifth. Apparatus to be used in carbonating oxide of lead substantially as set
forth under the fifth head.
Sixth. Apparatus for separating fine white lead from coarser particles, and
decolourizing and drying white lead substantially as set forth under the sixth head.
Seventh. The process and apparatus for the manufacture of white lead substan-
tially as herein set forth.
Dated the 20th day of February 1892.