Improvement in the Manufacture of White Pigments principally composed of Sulphate of Lead.
Year: 1889

page_text: Date of Application, 11th Dec., 1889
Complete Specification Left, 11th Sept., 1890-Accepted, 22nd Nov., 1890
PROVISIONAL SPECIFICATION.
Improvement in the Manufacture of White Pigments principally
composed of Sulphate of Lead.
I. JOHN EGERTON WOOD A.R.S.M. F.G.S. Temperance Hotel, Shirehampton,
near Bristol Manager of Works of Bristol Sublimed Lead Co. Limited Shirehampton
do hereby declare the nature of this invention to be as follows
--
My invention consists in the adding of some 5 to 10% of soda Na, CO, (5-10%
of the weight of white lead being operated upon) to water in which the white lead is
being washed. I say 5-10% more or less, as I have not had sufficient opportunity
for fixing the proportion. The soda may be dissolved in the water before the
addition of the lead; or it may he added with the lead; or after it. The "sublimed
lead" which I here call "white lead" is generally, lead sulphate with lead sulphite and
oxide, mixed with zinc oxide & smaller quantities of zinc sulphate and sulphite.
The sulphites usually are in very small quantities. This sublimed lead if ground
with oil, in the ordinary way of making paint, sets hard very often, like a cement ;
this setting taking place at once, or only after some time. Sublimed white lead
washed with water (this removes zinc sulphate and sulphite) & then dried no longer
has the power of setting when ground with oil. In this state however, used as a
paint on surfaces, it takes a considerable time to dry 5-6 days, which spoils its
chances as a paint. Sublimed white lead, washed or unwashed, rarely possesses
such a white colour as ordinary white or corroded lead.
This "sublimed white lead "treated or washed, according to my invention, fiitered
from the washing liquor & dried in the ordinary or any other way, is found to have
its colour greatly improved. It no longer sets on grinding; as far as I know, there
is no zinc lost by solution; and lastly it has a greater tendency to dry when used
as a paint.
101
D
1000
COMPLETE SPECIFICATION..
Improvement in the Manufacture of White Pigments principally
composed of Sulphate of Lead.
1, J. EGERTON WOOD Temperance Hotel Shirehampton near Bristol Manager to
The Bristol Sublimed Lead Co. Limited Works, Shirehampton near Bristol 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 consists in the washing of the dry pigment (i.e. not ground in oil)
with a solution of sodium carbonate or soda (Na, CO); by which process some lead
sulphate, and more or less of the lead oxide, and zinc salts are converted into
carbonates. Any zinc sulphate or zinc sulphite, which would tend to pass into
solution, would be converted into zinc carbonate. Any zinc oxide present would
be more or less transformed into carbonate. Generally speaking, the amount of
carbonate, formed in the pigment, is proportional to the soda used, and the time the
action is allowed to proceed.
Pigments consisting mainly of sulphate of lead, used as paint, have a very feeble
power of drying. Whereas ordinary white, or corroded lead, takes from one day to
three days to dry, when used in paint; pigments of the kind I have mentioned, would
probably take twice as long to dry. When a lead sulphate pigment, is ground stiff
with oil, in the ordinary manner, there is a tendency to set hard, as a cement, more

page_text: or less quickly. This usually occurs when zinc salts (sulphate, oxide and, or sulphite)
are present. When containing oxide of lead, a pigment of this kind, has, as a rule a
yellow tinge, which is objectionable.
The mode of precedure, with this invention is as follows.—The dry pigment to be
treated is stirred into a clear solution of soda. The proportions of soda and water,
are regulated by the nature of the pigment, and the mode of manipulating
respectively (by machinery hand &c.). With a pigment I have treated, which
consisted of some 86 % lead sulphate, 6% lead oxide, and the rest zinc oxide &c.,
I found that 5 per cent. of the pigiment, to be about the weight of soda required.
The muddy solution, is kept agitated for some hours, which in a case like that just
mentioned, would be some eight or ten. The clear liquor, which consists of a
solution of sodium salts (sulphate mostly) is got rid of, by any means (filter press,
syphon arrangement, or other means) and the pigment dried; it is then ready
for use.
.
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 :
1st. A total absence of any tendency of the pigment, so produced, to set, when
ground with oil.
99
1
J. EGERTON WOOD.