Process for Manufacture of White Lead.
Year: 1891

page_text: Date of Application, 3rd Mar., 1891
Complete Specification Left, 4th Jan., 1892-Accepted, 2nd Apr., 1892
PROVISIONAL SPECIFICATION.
A Process for Manufacture of White Lead.
1, JOHN HENRY NOAD, of No. 10 Lichfield Terrace, East Ham in the County
of Essex, Chemist and Electrician, do hereby declare the nature of this invention
to be as follows:-
My invention relates to the manufacture of white lead, by a process whereby I
obtain it of clear white colour and of good body suitable for pigment purposes.
In an electrolytic bath charged with solution of acetate of ammonia I suspend,
as anodes, slabs, bars or plates of lead, and as cathodes, slabs bars or plates of
other conducting metal, or it may be of carbon. I enclose the cathodes within
porous cells or in compartments separated from the rest of the bath by porous
partitions. I provide these cells or compartments and also the bath itself with
overflow pipes which communicate with a pipe supplying carbonic acid gas and with
a filter press.
I provide also means of pumping or forcing the liquids through the filter
press and of returning to the bath the liquid which is filtered out. The anodes
and cathodes being connected by suitable conductors to the terminals of a dynamo
electric machine or other source of electricity, after a time the liquid in the porous
cells or compartments is mostly ammonia solution, that in the rest of the bath
being mostly acetate of lead. Through the mixed liquid overflowing from both I
blow carbonic acid gas, sending the whole through the filter press, and returning to
the bath the liquid filtered out.
When this has gone on for some time I stop the action, or divert the liquids to
another filter press, and open apart the filter press which has been in use, removing
from it cakes of white lead precipitated in its cells from the liquid passed through.
Dated this 3rd day of March 1891.
ABEL & IMRAY,
Agents for the Applicant.
COMPLETE SPECIFICATION.
A Process for Manufacture of White Lead.
I, JOHN HENRY NOAD of No. 10 Lichfield Terrace, East Ham in the County
of Essex, Chemist and Electrician, 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 relates to the manufacture of white lead, by a process whereby
I obtain it of clear white colour and of good body suitable for piginent purposes.
In an electrolytic bath charged with solution-of acetate of ammonia I suspend,
as anodes, slabs, bars or plates of lead, and as cathodes, slabs bars or plates of
other conducting metal, or may be of carbon. I enclose the cathodes within
porous cells or in compartments separated from the rest of the bath by porous
partitions. I provide these cells or compartments and also the bath itself with
overflow pipes which communicate with a pipe supplying carbonic acid gas and
with a filter press.
I provide also means of pumping or forcing the liquids through the filter press
and of returning to the bath the liquid which is filtered out. The anodes and
cathodes being connected by suitable conductors to the terminals of a dynamo
electric machine or other source of electricity, after a time the liquid in the porous
cells or compartments is mostly ammonia solution, that in the rest of the bath
[Price 81

page_text: being mostly acetate of lead. Through the mixed liquid overflowing from both I
blow carbonic acid gas, sending the whole through the filter press, and returning
to the bath the liquid filtered out.
When this has gone on for some time I stop the action, or divert the liquids to
another filter press, and open apart the filter press which has been in use, removing
from it cakes of white lead precipitated in its cells from the liquid passed through.
I prefer to employ a ten per cent. solution of acetate of ammonia with a current
of a density of say four amperes to the square foot, and a pressure of about
one volt to each tank. The porous cells I make of Willesden water proof paper
of dimensions to contain a plate exposing four square feet of surface on either side.
Both the anodes and the cathodes I prefer to be of lead. The vats in which the
porous cells are contained may be of wood and of such dimensions as to contain a
number of porous cells either more or less to satisfy the above mentioned conditions
in regard to the supply of electricity.
Each vat and each cell in the vat is provided with an overflow or draw off pipe
and these all lead to a mixing tank. The arrangements are such that a tolerably
constant overflow is maintained from each cell and each vat; each cell supplying
its due proportion and the vat supplying to the mixing tank a quantity of liquor
equal to that drawn from all the cells which the vat contains.
Upon the bottom of the mixing tank there is a coil of pipe finely perforated and
carbonic acid gas is supplied to this pipe and is allowed to bubble through the
liquor which the mixing tank contains. The resulting precipitate should have a
creamy appearance; when it commences to have a granular look it is a sign that
the supply of carbonic acid gas is excessive. A force pump draws the liquor with
the precipitate suspended in it from the mixing tank and drives it into a filter
press.
The filter press I prefer to employ is that well known as Johnson's filter press
and in this press the white lead is collected between cloths in the form of cakes.
The liquor from the filter press is returned continuously to the vats and to the
porous cells.
As soon as a filter press is full it is detached and the contents are
washed by causing the force pump to force water through the cakes which the press
then contains.
The details of the apparatus and of the conduct of the manufacture may be much
varied without departing from my invention.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed I declare that
what I claim is :-
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1. The manufacture of white lead substantially as described by the electrolysis
of a solution of acetate of ammonia with anodes of lead and the treatment of the
resulting liquor with carbonic acid gas.
2. In the manufacture of white lead in accordance with the preceding claim, the
maintenance of a circulation from the vat in which the electrolysis is conducted,
through a carbonating apparatus and a filter press and back to the vat to be again
submitted to electrolysis.
Dated this 4th day of January 1892.