Improvements in and relating to the Manufacture of White Lead.
Year: 1897

page_text: Date of Application, 10th Mar., 1897
Complete Specification Left, 8th Dec., 1897-Accepted, 29th Jan., 1898
PROVISIONAL SPECIFICATION.
Improvements in and relating to the Manufacture of White Lead.
I, THOMAS CRISP SANDERSON, of Brooklyn, Humber Road, Westcombe Park, in
the County of London, Metallurgist, do hereby declare the nature of this invention
to be as follows:-
The improvements which form the subject of my application for Letters Patent
are devised to produce a precipitated white lead of high density and having a com-
position similar to that produced by what is known as the "Dutch" or
process.
stack"
It is wellknown that white lead can be made by a precipitation process of com-
position simiar to that produced in the Dutch process namely in the form of a
compound or mixture of carbonate and hydrate of lead, but such precipitated
white lead has usually suffered from the drawback of being of very light density
which constitutes an objection to its commercial use. Furthermore, it may be
found that in two samples, the one produced by the Dutch process and the other
by precipitation each may be of identical per centage composition of carbonate and
hydrate of lead and even of the same specific gravity when the respective powders
are weighed in water and yet the weight of equal bulks of the dry powders when
weighed in air may be very different, the precipitated sample being considerably
lighter. By my improved process I succeed in precipitating upon the first pre-
cipitated bulk of mixed carbonate and hydrate of lead further quantities which
produce a body of essentially the same physical qualities as the Dutch process
white lead and approximately of the same specific gravity in air as well as in water.
In carrying my invention into effect I treat in a suitable vessel a charge of
basic acetate of lead solution by blowing carbonic acid gas from a suitable source
through the same until a precipitate of carbonate and hydrate of lead is thrown
down. After the precipitate has been allowed to settle I draw off the clear normal
acetate solution, I then run a fresh charge of basic acetate solution into the vessel,
intermix therewith the precipitate already obtained by stirring the same
thoroughly and treat the whole mixture again with carbonic acid gas as before.
This operation may be repeated as frequently as is found to be requisite. Finally,
the precipitate is run or pumped into filter-presses or settlers to separate it from
the liquid after which it is washed and dried in the usual manner. It will be
found that the precipitate thus prepared is of much greater density than the same
precipitate produced by a single operation. The proportion of carbonate and
hydrate in the precipitate can be varied within certain limits by the amount and
composition of the gas injected into the solution. It is advantageous to keep the
precipitate agitated during the operation by means of a stirrer or agitator working
near the bottom of the vessel. When sufficient carbonic acid gas has been blown
through the solution in order to reduce the basic acetate to the normal acetate of
lead the gas is stopped and the precipitate allowed to subside, but it is better to
prevent it from setting fast on the bottom by sufficiently agitating by means of
the stirrer.

page_text: In place of conducting the whole operation in a single tank I find it advantageous
on the manufacturing scale to draw off the whole or part of the precipitated white
lead into a second vessel or tank also provided with a stirrer and there to pre-
cipitate another charge of basic acetate upon it in the same manner, repeating
the operation as often as requisite to produce the required density and composition.
The resultant normal acetate after being drawn off the precipitate is again used to
produce basic acetate by resaturating with lead oxide in the well known manner,
any loss of acid being replaced by the addition of acetic acid' and the first washings
from the white lead.
j
.
Although I have described my process as applicable to the precipitation of white
lead from acetic acid solution, it is also applicable to other soluble salts of lead
capable of being precipitated by carbonic acid gas for this purpose.
Improvements in and relating to the Manufacture of White Lead.
I, THOMAS ('Ise Sanderson, of Brooklyn, Humler Road, Westcombe Park, in
the franty of London, Met Murgist, da hereby declare the nature on 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 of an improved process for the manufacture of white lead
of high density.
White lead as is well known has hitherto been made principally by reacting
upon metallic lead by means of moist air containing vapour of acetic acid and
carbonic acid in the manner known in England as the "Dutch" or
"Stack
process. A product of like chemical composition can be more economically and
quickly produced by precipitation of a suitable lead salt, but such precipitated pro-
ducts have hitherto been of too light density. It is found that when the chemical
composition of the respective products is the same, and even when they are of the
sume specific gravity when weighed in water, the weight in air of equal bulks of
the products will shew considerable difference, the precipitated article being much
lighter.
By my improved precipitating process I produce a new kind of precipitated white
lead equal in its physical qualities to that produced by the slower and more expen-
sive oxidation process.
In carrying my invention into effect I treat in a suitable vessel a charge of basic
acetate of lead solution by blowing carbonic acid from a suitable source through
the same until a precipitate of carbonate and hydrate of lead is thrown down. After
the precipitate has been allowed to settle I draw off the clear normal acetate solu-
tion; I then run a fresh charge of basic acetate solution into the vessel, intermix
therewith the precipitate already contained by stirring the same thoroughly, and
treat the whole mixture again with carbonic acid as before. This operation may
be repeated as frequently as is found to be requisite. Finally, the precipitate is
run or pumped into filter-presses or settlers to separate it from the liquid after
which it is washed and dried in the usual manner. It is advantageous to keep the
precipitate agitated during the operation by means of a stirrer or agitator working
near the bottom of the vessel. It will be found that the precipitate thus prepared
is of much greater density than the same precipitate produced by a single opera-
tion. In preparing a white lead containing definite proportions of plumbic hydrate

page_text: and carbonate respectively, I attain the object in view by varying the number of
successive precipitations, or the amount of precipitate carried over at each succeed-
ing precipitation. When sufficient carbonic acid has been blown through the solu-
tion in order to reduce the basic acetate to the normal acetate of lead the supply
of carbonic acid is stopped and the precipitate allowed to subside, but it is better
to prevent it from settling fast on the bottom by sufficiently agitating by means
of the stirrer.
In place of conducting the whole operation in a single tank I find it advan-
tageous on the manufacturing scale to draw off the whole or part of the precipi-
tated white lead into a second vessel or tank also provided with a stirrer and there
to precipitate another charge of basic acetate upon it in the same manner, repeating
the operation as often as requisite to produce the required density and composition.
The resultant normal acetate after being drawn off the precipitate is again used
to produce basic acetate by resaturating with lead oxide in the well known manner,
any loss of acid being replaced by the addition of acetic acid and the first washings
from the white lead.
Although I have described my process as applied to the precipitation of white
lead from acetic acid solution, it is also applicable to other soluble salts of lead
capable of being precipitated by carbonic acid for this purpose.
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:
:―
1. The production of precipitated white lead of high density by adding succes-
sive quantities of carbonic acid to a basic lead salt solution in presence of the
successive precipitates accumulated from prior precipitations.
2. The herein before described process for the production of commercial precipi-
tated white lead of high density by precipitating successive precipitates by means
of carbonic acid from a solution of basic acetate of lead or the like, separating the
supernatant liquid from the precipitate, and adding a further supply of solution
thereto before each precipitation, substantially as and for the purpose set forth.
3. In a process for the manufacture of white lead by precipitation of a lead salt
from solution by means of carbonic acid, the obtaining of a precipitate containing
plumbic hydrate and carbonate in definite proportions, substantially as set forth.
OT J
1
1007
W. P. THOMPSON & Co.,
Of London, Liverpool, Manchester and Birmingham,
Patent Agents for the Applicant.