Improvements in the Manufacture of White Pigment.
Year: 1886

page_text: Date of Application, 11th Aug., 1886.
Complete Left, 10th June, 1887.
Complete Accepted, 2nd Aug., 1887.
PROVISIONAL SPECIFICATION.
Improvements in the Manufacture of White Pigment.
I FARNHAM MAXWELL LYTE of Cotford Oakhill Road Putney in the County of
Surrey Analytical Chemist do hereby declare the nature of this invention to be as
follows:-
In addition to the methods described in a previous application for Letters Patent
No. 8837 of 1886 and entitled "Improvements in the production of White Pigments,"
I find that the oxy or basic salts of lead fitted for use as pigments may conveniently be
produced by adding to one of the basic salts of that metal in solution, an acid producing
insoluble or sparingly soluble compounds with lead; or by adding a solution of one of
the salts of any such acid to a solution of one of the soluble basic salts of lead. The
addition, however, of acids must be in given proportions and according to the chemical
formulæ, otherwise the composition of the precipitate is liable to vary according to the
proportion of the precipitant used, and if a salt is employed the compound generated
often possesses a more or less solvent action on the precipitated lead salt.
Another way is to digest an insoluble or sparingly soluble salt of lead whether
normal or basic with one of the soluble basic lead salts. By this last method also, the
normal, or more or less basic salt of lead thrown down by an acid from the normal or
basic soluble salt of lead as first above described, as well as the Clichy white lead, may,
when not sufficiently basic, be improved.
Again, where, in working according to my Patent above mentioned, an excess
of PbO may have been accidentally added, causing the pigment or paint made there-
from to lose whiteness, such over basic lead pigment may be brought to its proper
basicity by digestion with a suitable acid, or with a solution of one of its salts, thus
dissolving the excess of PbO while the insoluble lead salt retains that basicity to which
it owes its covering power as a pigment.
In producing precipitates according to the above described methods, I may find it
advantageous to heat the solutions. I further find that precipitates thus produced may,
in certain cases, to advantage, be mixed with the oxides or insoluble compounds of
some of the other metals.
F. MAXWELL LYTE.
By A. M. & Wm. Clark,
53, Chancery Lane, London,
Patent Agents.

page_text: 1 FARNHAM MAXWELL LYTE of Cotford, Oakhill Road, Putney in the County of
Surrey, Analytical Chemist 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 :-
It is generally admitted that the covering power of carbonate of lead is partly due
to its degree of basicity; the same peculiarity is, however, generally an attribute of
other insoluble or sparingly soluble lead salts such for instance as the sulphate, chloride,
oxalate, and phosphate; and I have found that these, as well as the carbonate, may be
brought to any required degree of basicity by digestion, under the action of heat, in
a soluble basic lead salt such, for instance, as the basic acetate or nitrate of lead.
I find that lead sulphate and lead chloride both give good results, and I will describe
my invention as applied to the treatment of lead sulphate, it being understood however,
that I do not limit myself to this salt.
The following is an example of a method of carrying out my process; I take, say,
about 100 gallons of basic lead acetate (made for instance by repeatedly pouring
a neutral lead acetate of, say, specific gravity 1.15 at 60° Fahrenheit, over finely
divided lead) of specific gravity about 1.315 at 60° Fahrenheit, and I precipitate the
said 100 gallons with sulphuric acid until the liquid becomes so barely acid that it will
turn litmus paper plum color. I then heat this acidulated liquor (say, to boiling point
in a steam-jacketted pan) and after allowing about an hour for the precipitate to settle,
I decant the acidulated effluent. This effluent may again be rendered basic by pouring
it over finely divided lead, as above described, a further quantity of acetic acid being
added, if necessary. To the lead sulphate precipitate left in the pan, I then add a
further quantity (say, 50 gallons more or less, according to the basicity it is required
to impart to the precipitate) of the same basic acetate, that is to say, having in the
first instance precipitated all the extra base out of 100 gallons of a given basicity, I
then add to the precipitate, another measure of liquor containing a given proportion of
base. I then proceed to heat this liquor (containing the precipitated sulphate) proferably
to 212° Fahrenheit, and continue boiling and stirring for about a quarter of an hour.
By this time, it will be found that the sulphate has attained its right degree of basicity,
the liquor on the other hand having lost most of its extra base. The whole may then
be filter-pressed and the filtrate added to the before mentioned acidulated effluent for
re-conversion into basic acetate. The cakes from the filter press should then be
broken up and washed and, if necessary, the operation of washing repeated until the
washings are barely clouded on addition of sulphuric acid. The washed basic sulphate
may now be dried and powdered, in the manner usual in the manufacture of Dutch
Lead, and packed for sale; but I find that it is improved if ground either when moist
or dry, but before being mixed with Oil.
The first washings which contain a considerable proportion of acetate, may be
treated with sulphuric acid and the lead sulphate precipitated (when washed) may be

page_text: added to the next batch of lead sulphate to be rendered basic, or it may be treated
separately with a given proportion of basic acetate, as hereinafter described, or
it may even be added to the next batch of basic lead sulphate after the boiling, as the
presence of such a small proportion of normal sulphate is immaterial. The last
washings are not worth treatment.
I would have it understood that I do not limit myself to the specific gravities above
given, although I find them answer very well.
When it is desired to render basic a salt not specially precipitated, as above described,
(such for instance, as the sulphate precipitated as a bye-product by the makers of red
liquor for print works) I may estimate the weight of the extra base when precipitated
with H. SO, from one gallon of the basic acetate to be employed and then (supposing
this to be two pounds or thereabouts when dry) for every two pounds of red liquor
precipitate well washed and dried, I add one gallon (more or less according to the
degree of basicity required) of the basic acetate and boil the same, as before described.
It is however, preferable not to dry the precipitates before boiling with the basic
acetate and this may be avoided, by estimation of moisture. Or, inasmuch as it may
be easily calculated how much precipitate, sulphate, or otherwise, any given salt of
lead will give, it will be easy, knowing the quantity of that salt which has been used,
to find out by calculation, with how much basic acetate or other basic solution, to boil.
Although I have described a volumetric method of treatment, I desire it to be
understood that I do not specifically claim this method in the present application, as it
forms the subject of another application for Letters Patent, bearing date September 18th
1886 No. 11889.
As silver and other metals may be recovered from the bottom of the lead acetate
tubs, the process thus becomes a cheap method of treating silver lead in the manufacture
of White Lead.
Having now particularly described and ascertained the nature of the said
invention, and in what manner the same is to be performed; I declare that what I
claim is;-
"
The herein described process of rendering basic, lead sulphate and lead chloride and
other normal or partly basic insoluble or sparingly soluble lead salts; which process
consists, essentially, in digesting, with heat, the salt to be rendered basic in a solution
of basic lead acetate or other basic soluble salt of lead, substantially as and for the
purpose specified.
F. MAXWELL LYTE.
By A. M. & Wm. Clark,
53, Chancery Lane, London,
Patent Agents.