Improvements in the Manufacture of White Lead.
Year: 1889

page_text: Date of Application, 22nd Oct., 1889
Complete Specification Left, 27th Jan., 1890-Accepted, 15th Mar., 1890
PROVISIONAL SPECIFICATION.
Improvements in the Manufacture of White Lead.
I, Professor Dr. PAUL BRONNER of Stuttgart, in the Empire of Germany, do hereby
declare the nature of this invention to be as follows:-
The method of manufacturing white-lead, which forms the subject of this invention
is based upon the discovery which I have made that lead sulphate can be very readily
decomposed by heating it together with a certain quantity of soda-lye if this quantity
be determined so that the product will be, not hydrated oxide of lead, but a basic salt.
If this quantity be such that the compound 2 Pb SO, Pb (HO), is produced the
latter can immediately be transformed into excellent white-lead 2 Pb CO₂, Pb (HO),
by heating the same together with a suitable quantity of sodium carbonate. The
by-product obtained is Glauber's salt.
The lead sulphate which has been freshly precipitated (not dried) and purified by
washing is heated, together with 2 molecules of caustic soda for 3 molecules of the
sulphate the basic salt 2 Pb SO, Pb (HO), being very readly formed:
2 Pb SO, Pb (HO), + 2 Na, CO₂
===
2 Pb CO₂, Pb (HO), + Na, SO..
The solution of Glauber's salt at the top of the basic lead sulphate need not be drawn
off. In fact the necessary quantity of the solution of soda can be added immediately,
the heating being then continued. It is however expedient to take somewhat more
soda than the quantity determined by calculation because a small excess of the same
will greatly facilitate the transformation. (The lead sulphate may however be treated
directly with a mixture of soda-lye and soda.) The crumbly condition of the precipitate
gradually disappears and the latter becomes finely pulverized, its volume being
perceptibly decreased by the change. The termination of the transformation may be
roughly ascertained by the alkaline reaction becoming considerably weaker but the
surest indication of the end is that a well-washed sample dissolves without a residuum
in heated, diluted pure nitric acid or in acetic acid. The solution, which contains
Glauber's salt, is drawn off whilst the white-lead is washed, pressed and dried.
By the improved process a very beautiful and extremely fine product is obtained
which has excellent covering-power and renders grinding and pounding unnecessary.
The cost of this process compares favorably with that of the so called stack or chamber
process.
This process enables the lead sulphate obtained as a by-product in cloth-printing
works in the preparation of the red-mordant to be transformed with profit into saleable
white-lead. It is of course understood that the sulphate can also be produced at will

page_text: from litharge or from sugar of lead or lead nitrate, and treated so as to obtain white
lead at a comparatively low price.
Dated this 22nd day of October 1889.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, Agents for the Applicant.
The transformation rapidly takes place even up to 70 degrees Centigrade, and a
swollen, crumbly substance is produced which tends to ball so as to form lumps. This
balling must be prevented by continual stirring. The termination of the transformation
is easily perceived by the complete disappearance of the alkaline reaction. This basic
sulphate cannot be employed as a pigment because it does not possess sufficient covering
power. It can however be completely decomposed by heating the same together with
à solution of sodium carbonate (soda) and transformed into white-lead.
2 Pb SO, Pb (HO)2 + 2 Na₂ CO₂ = 2 Pb CO₂, Pb (HO)2 + 2 Na, SO..
The solution of Glauber's salt at the top of the basic lead sulphate need not be drawn
off. In fact the necessary quantity of the solution of soda can be added immediately,
the heating being then continued. It is however expedient to take somewhat more
soda than the quantity determined by calculation, because a small excess of the same
will greatly facilitate the transformation. (The lead sulphate may however be treated
directly with a mixture of soda-lye and soda.) The crumbly condition of the
precipitate gradually disappears and the latter becomes finely pulverized, its volume
being perceptibly decreased by the change. The termination of the transformation
may be roughly ascertained by the alkaline reaction becoming considerably weaker,
but the surest indication of the end is that a well-washed sample dissolves without a
residuum in heated, diluted, pure nitric acid or in acetic acid. The solution, which
contains Glauber's salt, is drawn off, whilst the white-lead is washed, pressed and
dried.
By the improved process a very beautiful and extremely fine product is obtained
which has excellent covering power and renders grinding and pounding unnecessary.
The cost of this process compares favorably with that of the so called stack or chamber
process.

page_text: This process enables the lead sulphate obtained as a by-product in cloth-printing
works in the preparation of the red-mordant to be transformed with profit into saleable
white-lead. It is of course understood that the sulphate can also be produced at will
from litharge or from sugar of lead or lead nitrate and treated so as to obtain white-
lead at a comparatively low price.
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 is ;-
The process of transforming lead sulphate first into basic sulphate preferably into
2 Pb SO, Pb (HO), by heating it with caustic alkaline lye and then into white lead
by heating the basic sulphate with carbonate of sodium.
Dated this 27th day of January 1890.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, Agents for the Applicant.