IMPROVEMENTS IN OBTAINING COMPOUNDS OF LEAD SUITABLE FOR MAKING PIGMENTS AND FOR OTHER PURPOSES
Year: 1883

page_text: LETTERS PATENT to Andrew French, of Morriston, in the County of
Glamorgan, Metallurgist for an Invention of “IMPROVEMENTS IN OBTAINING
COMPOUNDS OF LEAD SUITABLE FOR MAKING PIGMENTS AND FOR OTHER
PURPOSES
"
PROVISIONAL SPECIFICATION left by the said Andrew French at the
Office of the Commissioners of Patents on the 1st November 1883.
ANDREW FRENCH, of Morriston, in the County of Glamorgan, Metallurgist
"IMPROVEMENTS IN OBTAINING COMPOUNDS OF LEAD SUITABLE FOR MAKING
PIGMENTS AND FOR OTHER PURPOSES”
This Invention relates to the treatment of sublimed whito lead or the compound
obtained by the processes described in the Specification of Letters Patent granted
to the present applicant and dated 8 June 1881 (Nº 2494).
One of the present improvements consists in treating the sublimato so as to
produce a white pigment or substance of very pure color and having a less capacity
or absorbing power for oil, whilst retaining all the other good properties of the
sublimate.
By a second modification of the improved treatment a dark red or brown
compound of lead is obtained which is advantageously applicable for painting and
other purposes.
In carrying out the first improvement the sublimate is treated with sufficient
hydrochloric acid to combine with the zinc and the unsaturated oxide of lead
when present. The acid may either be added directly, but gradually, in the wet
condenser employed for collecting the sublimate; or it may be added to the
sublimate after it has been collected. If the acid is added in the condenser care
must be taken that the water does not become strongly acid. The sublimate
having been treated with the acid may be dried at onco, or it may first be washed
BO as to remove all the soluble zinc chloride and then be dried for the market.
In either case it forms- an excellent white pigment, and requires very little oil to -
form white lend of the usual consistency.

page_text: -
The same treatment may also be employed when sublimed oxides of lead are
produced from crude oxides, or litharge, or metallic lead, the acid being used in
quantity not more than sufficient to produce a white substance of the kind formerly
known as Pattinson's oxychloride of lead.
To obtain the dark red or brown pigment or substance the wet sublimate
consisting principally of sulphite or oxysulphite of lead, has mixed with it a
quantity of what is known as chloride of lime or bleaching powder. The substance
first changes to a light yellow and passes through successively deeper shades until
it becomes dark red or brown. It must then be treated with boiling water to
remove soluble matters, and afterwards dried. When dried it can be ground in
oil and forms a good paint, whilst it is applicable for all the uses to which red lead
is put by ongineers as it has strong drying properties.
SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Andrew French in the Patent Office on the 30th April 1884.
ANDREW FRENCH, of Morriston, in the County of Glamorgan, Metallurgist, 1
"IMPROVEMENTS IN OBTAINING COMPOUNDS OF LEAD SUITABLE FOR MAKING
PIGMENTS AND FOR OTHER PURPOSES"
. My said Invention relates to the treatment of sublimed white lead or the
compound obtained by the processes described in the Specification of Letters
Patent granted to me and dated 8 June 1881. N° 2494.
One of my present improvements consists in treating the sublimate so as to
produce a white pigment or substance of very pure color, and having a less
capacity or absorbing power for oil, whilst retaining all the other good properties
of the sublimate. This pigment or substance has also the advantage of being
incapable of passing through the pores of the skin of persons handling it as it is
insoluble in lactic acid a constituent of sweat which easily dissolves ordinary white
lead and thereby facilitates its introduction into the system. My improved pigment
does not darken so readily as the best white lead by exposure to foul gases or by
absence of sunlight.
By a second modification of my improved treatment a dark red or brown
compound of lead is obtained which is advantageously applicable for painting
and other purposes.
In carrying out my first improvement the sublimate is treated with sufficient
hydrochloric acid to combine with the zinc and any unsaturated lead which may
be present. The acid may either be added directly but gradually in the wet
condenser employed for collecting the sublimate or it may be added to the
sublimate after it has been collected. In the acid is added in the condenser care
must be taken that the water does not become strongly acid. The sublimate
having been treated with the acid may be dried at once, or as I prefer, it may
first be washed so as to remove all the soluble zinc chloride and then be dried.

page_text: In either case it forms an excellent white pigment requiring very little oil to form
white paint of the consistency of ordinary white lead.
The sublimate for treating which my present Invention is designed consists of
lead and zinc, the zinc being in small but variable proportions ranging from 3
to 15 per cent. Sometimes a little alumina and traces of iron are present, being
derived from the fuel, the iron being occasionally sufficient to give a slight tawny
tint to the sublimate. The metals are in the state of sulphites if the ore or other
material from which they have been produced consisted of sulphides.or sulphates,
with only a small amount of oxide of lead; but if much of the latter is present
in the smelting material the sublimate will consist of sulphites and oxides, the
proportions of which will depend on the amount of sulphur in the smelting
material. A considerable part of the sulphite of zinc present is in the free state
and may be dissolved out by water; the remainder of the zinc boing like the
lead as sulphite and oxide in combination and soluble only in one of the stronger
acids.
With hydrochloric acid the whole of the zino may be dissolved out of the
sublimate without decomposing the lead compounds, provided the quantity of acid
is not much more than that required to convert all the zinc into chloride. By
using only a little more acid than is required to convert the zino into chloride, the
alumina and iron will also be dissolved, and that, without disintegrating the
particles of lead compounds but only having the effect of roughening their surfaces
and rendering them whiter and more opaque. This roughening, which can be
observed by means of a microscope, enables the particles to adhere closely together
under slight pressure thereby increasing the density of their aggregations, and
diminishing the proportion of surface to mass, so that a comparatively small
quantity of oil is required for making up the substance into a paint.
In practically working the first part of my Invention I employ both modes of
treatment herein before described, adding acid to the sublimate deposited in and
collected from the Blues between the furnaces and the wet condenser, and also adding
acid to the water in the condensor. In the condenser the acid must be added very
gradually and only so as to keep the water just sharpened or distinctly acid, from
two to five per centum of real acid in the water being sufficient. As the acid
becomes neutralised by the sublimate more must be added to the water to maintain
the proper strength.
The sublimato thus treated in the condenser is run off at convenient periods and
washed with fresh water in a "dolly tub" having a rotating agitator, so as to
dissolve and wash out any adhering chloride of zinc or free acid. The washod
sublimate is next transferred to settling tanks and is afterwards dried in a stove.
The dried cake is passed through a mill having light rollers and is crushed and
afterwards sifted, and it may then be combined with oil in the usual way or it may
be sold as dry white lead.
In treating the dry sublimate collected from the flues or obtained by drying
what is collected in the wet condenser (without having added acid) about one part
by weight of commercial hydrochloric acid (of a specific gravity of about 1·050 or
25 per cent real acid) is mixed, in the cold with every four parts of the sublimate,
in a suitable mill preferably made of sandstone and having wooden or leaden
mixers. This quantity of acid will suffice for treating a sublimate which does not
contain more than 8 per cent of zinc. When the sublimate contains say 15 per
cent of zinc the quantity of acid required will be about one third that of the
sublimate. After the charge has been well mixed it must be allowed to stand for a
fow hours, after which it should be well washed, taking small quantities at a
time, in a "dolly tub" of the kind hereinbefore mentioned. The remainder of
the treatment may be the same as for the washed product of the sublimate treated
with acid in the condenser.
To obtain the dark red or brown pigment (which chemically consists of peroxide
of lead and a sulphur compound of lime) a strong solution is prepared of "chloride
of lime" (bleaching powder) and the sublimate is added to it gradually with brisk

page_text: agitation. The proportion of chloride of lime required to change the sublimate to
a dark brown is about one part to two and a half parts of the sublimate'; but if a
less complete change is desired a smaller proportion of the chlorine agent must bo
used. The operation of mixing should be conducted in a closed vessel having a
flue for conducting the chlorine gas which is abundantly evolved to chambers -
supplied with lime so as to recover the chlorine as chlorido of lime to be used in
treating further quantities of sublimate. Or the chlorine gas may be used in any
other way. The dark red or brown product obtained is washed and dried and may
bo combined with oil to form a paint It dries well and is durable; and is a good
substitute for red lead as used by engineers.
Having thus particularly described my said Invention and the manner of
performing the same I have to state that I do not restrict myself to the preciso
details herein described but that what I believe to be novel and original and claim
as the Invention secured to me by and in terms of the hereinbefore in part recited
Letters Patent is :-
1. The process of treating a sublimate consisting principally of sulphite of lead
with hydrochloric acid substantially in the manner and for the purposes hereinbefore
described.
2. The process of treating a sublimate consisting principally of sulphite of lead
with chloride of lime (bleaching powder) substantially in the manner and for the ?
purposes hereinbefore described.
In Witness whoreof I, the said Andrew French, have hereunto set my hand and
seal this twenty-fifth day of April in the year of our Lord One thousand eight
hundred and eighty-four.
ANDR
VAT