Process for Manufacture of White Lead.
Year: 1890

page_text: Date of Application, 24th July, 1890
Complete Specification Left, 23rd Apr., 1891-Accepted, 30th May, 1891
PROVISIONAL SPECIFICATION.
A Process for Manufacture of White Lead.
I, GUSTAV BISCHOF of No. 4 Hart Street, Bloomsbury, in the County of
London, Professor of Chemistry do hereby declare the nature of this invention to
be as follows:-
In manufacturing white lead by acting with carbon dioxide on a lead oxide in the
presence of suitable reagents such as acetic acid or its compounds, great difficulty
is experienced in obtaining for this purpose an oxide such as will produce white
lead of a clear white colour. One cause of this difficulty seems to be that lead
oxides of commerce, such for instance, as litharge, are mixtures of several com-
pounds of lead with oxygen, which are differently acted on by the reagents
employed, so that some of these oxides become converted before others of them,
and when the reaction is continued in order to convert those others, those first
converted are apt to be rendered crystalline, thus greatly impairing the value of
the product.
My invention relates to a process whereby I can overcome the difficulty above
stated, and can obtain from ordinary mixed lead oxides a clear uniform white
lead without crystals, in the following manner.
I first partially deoxydise the crude lead oxides, by exposing them at a
temperature of 250° to 300° C. to the action of gas rich in hydrogen, such for
instance as water gas. This operation may be conducted in revolving vessels, or
in stationary vessels provided with agitators, and with suitable worms or other
conveyors for delivering the partially deoxidised product, which is thus reduced to
the condition of suboxide of lead (Ph,O). As it is of advantage to cool the
product before it leaves the deoxidising atmosphere, the delivery passage or
passages should be water jacketted or otherwise kept cool. Having thus reduced
the material to the uniform condition of suboxide, I hydrate and oxidise it by
slaking it with water and exposing it to the air, the suboxide being thus con-
verted into a higher oxide, probably monoxide. Finally, I subject this oxide
mixed with water, sugar and acetic acid or an acetate, such as acetate of lead,
to the action of carbon dioxide. The proportions of the charge may vary;
practically I find a suitable proportion to be:-Hydrated lead oxide about
900 lbs., water about 250 gallons, commercial acetic acid equivalent to about 14 lbs.
of the pure chemical-acid, (or the equivalent of this in lead acetate) and sugar
about 45 lbs. The liquid portion of the charge, after the white lead is separated
from it, may be used with successive charges of lead oxide.
This operation is conveniently performed in revolving vessels, the gas, when it is
pure, being admitted through a trunnion under a little pressure.
When the carbon dioxide gas is mixed with air or other gases, it is of advantage
to employ in rotation a series of carbonating vessels with inlet through the one
trunnion and outlet through the other, so that the surplus gas can be conducted
from the one to the next in order, until the whole of the carbon dioxide or nearly
the whole is absorbed.
בד
71
1
CTI
1000
ABEL & IMRAY,
Agents for the Applicant.

page_text: COMPLETE SPECIFICATION.
A. Process for Manufacture of White Lead.
I, GUSTAV BISCHOF, of No. 4 Hart Street, Bloomsbury, in the County of
London, Professor of Chemistry, '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 :-
In manufacturing white lead by acting with carbon dioxide on a lead oxide in
the presence of suitable reagents such as acetic acid or its compounds, great
difficulty is experienced in obtaining for this purpose an oxide such as will produce
white lead of a clear white colour. One cause of this difficulty seems to be that
lead oxides of commerce, such for instance as litharge, are mixtures of several
compounds of lead with oxygen, which are differently acted on by the reagents
employed, so that some of these oxides become converted before others of them;
and, when the reaction is continued in order to convert those others, those first
converted are apt to be rendered crystalline, thus greatly impairing the value of
the product.
My invention relates to a process whereby I can overcome the difficulty above
stated and can obtain from ordinary mixed lead oxides a clear uniform white lead
without crystals, in the following manner :-
I first partially deoxidise the crude lead oxides by exposing them at a
temperature of about 250° to 300° C. to the action of gas rich in hydrogen such
for instance as water gas; but care should be taken to avoid the presence of
sulphur compounds.
This operation may be conducted in revolving vessels, or in stationary vessels
provided with agitators and with suitable worms or other conveyors for delivering
the partially deoxydised product which is thus reduced to the condition of sub-
oxide of lead, probably corresponding to the formula Pb,O. As it is of advantage
to cool the product before it leaves the deoxidising atmosphere, the delivery
passage or passages should be water jacketted or otherwise kept cool.
Having thus reduced the material to the uniform condition of suboxide, I hydrate
and oxidise it by moistening it with water and exposing it to the air, the suboxide
being thus converted into a higher oxide, probably monoxide, which may be
expressed by the formula PbH,O2.
Finally, I subject this oxide mixed with water and acetic acid or an acetate, such
as acetate of lead, and preferably with sugar, to the action of carbon dioxide.
The proportions of the charge may vary; practically I find a suitable proportion
to be :-
Hydrated lead oxide about 900 lbs., water about 250 gallons, commercial
acetic acid equivalent to about 14 lbs. of the pure chemical acid (or the equivalent
of this in fead acetate) and sugar about 45 lbs. The sugar however is not
absolutely necessary, but is useful in promoting the reaction. The liquid portion
of the charge after the white lead is separated from it, may be used with
successive charges of lead oxide.
This operation is conveniently performed in revolving vessels, the gas, when it is
pure, being admitted through a trunnion under a little pressure.
When the carbon dioxide gas is mixed with air or other gases, it is of advantage
to employ in rotation a series of carbonating vessels with inlet through the one
trunnion and outlet through the other, so that the surplus gas can be conducted
from the one to the next in order, until the whole of the carbon dioxide or
nearly the whole is absorbed.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed I declare that what I
claim is :-
The herein described process for manufacture of white lead, by reducing the

page_text: mixed lead oxides of commerce to the condition of suboxide, oxidising and hydrating
this product and subjecting it in admixture with water acetic acid or acetates, with
or without sugar, to the action of carbon dioxide.
11001
ABEL & IMRAY,
Agents for the Applicant.