Improvements in and relating to the Manufacture of White Lead.
Year: 1892

page_text: Date of Application, 13th Aug., 1892-Accepted, 8th Oct., 1892
COMPLETE SPECIFICATION.
Improvements in and relating to the Manufacture of White Lead.
I, ARTHUR JAMES SMITH, of Kingston-on-Thames, in the County of Surrey,
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 :-
The main object of my invention is to provide for the production of a pure white
lead containing the proper percentage of the actual pigment compound (that is to
say, of the minute rounded and opaque particles which have no signs of crystal-
lization) necessary to impart to the paint or pigment as high a covering power as
is practically consistent with the preservation of the requisite capacity for
effecting the solidification or drying and hardening of the oil used in the paint
or pigment, such percentage being much larger than that contained in white lead
made by any of the processes heretofore devised.
My said invention is, moreover, designed to provide for the manufacture of good
commercial white lead in a more expeditious and effective manner and at a much
lower cost than is practicable by the processes hitherto devised.
As is well known, the process heretofore usually adopted for the manufacture of
white lead, is that commonly termed the Dutch process, which consists in placing
coiled sheets or cast gratings of metallic lead in pots containing dilute acetic acid,
and packing such pots in a bed of stable-manure or spent tan-bark, one layer of
pots being arranged above another. This process is both uncertain and slow in its
action and has the further disadvantage of great risk to the operatives by reason of
the fumes and dust of lead given off during the operations.
Many attempts have been made to devise cheaper, more perfect and expeditious
processes for the production of white lead from blue or metallic lead, but such
processes are all more or less unsatisfactory and some of them are impracticable
for the reasons hereinafter mentioned.
In some of the Specifications of prior Letters Patent in which processes of
this kind are described, it is stated that the lead is subjected alternately to the
action of acetic acid vapour (with or without steam and atmospheric air) and
to the action of carbonic acid gas; and, in a few cases, it is also stated that,
previous to this treatment, the lead is dipped into or sprinkled with a solution,
consisting, for example, of a mixture of acetic acid or nitric acid or both with a
solution of acetate or nitrate of lead. But the directions given in the said prior
Specifications are not such as would enable any person skilled in the art of manu-
facturing white lead to successfully manufacture white lead by the processes
described. And, as far as I am aware, none of the said processes have ever
been carried into practice on a commercial scale.
Amongst the chief causes of failure of such processes, I would mention the
following, ci. -The lack of proper proportion between the dimensions of the lead
strips or cuttings and the height of the pile of the said strips or cuttings on the
trays in the corroding or converting chambers, and the consequent insufficiency
of the vapour ways through the charge. The want of proper relative duration
of the periods of treatment with acid vapours, steam, atmospheric air, and
carbonic acid gas, and the want of variation in the strength and concentration
of the acids. The presumption that all portions of the entire charge must be
treated alike, notwithstanding the fact that the corrosion always takes place
unequally throughout the charge, and therefore different portions of the charge
require to be differently treated according to their more or less corroded condition
at various periods or stages of the process. In short, I would say that the processes.
heretofore described have been unsuccessful because of the lack of this and other

page_text: knowledge as to how to properly control the chemical actions comprised in the
corrosion of the lead.
In the Specification of former Letters Patent dated 15th September 1882
No. 4405, I have described a process of manufacturing white lead, and, in that
Specification, it is stated that the metallic lead is first formed into fine threads
or fibres in order to present a very extended surface to the action of the corroding
agents and to provide suitable vapour ways through the charge. But I have since
found that the threads or fibres of lead described in the said former Specification
are much too fine to produce the desired results, the dimensions thereof, as stated in
the Specification, being three-fourths of a millimetre in breadth by one-fourth of a
millimetre in thickness at the centre; and I have also ascertained that the height
of the pile of the said threads or fibres, as stated in my said former Specification,
viz. About fifty millimetres, is much too great in proportion to the dimensions
of the lead fibres.
Since lodging the Complete Specification of the said former Letters Patent, I
have found, after a great number of experiments and practical trials of the
process, that, with such fine threads or fibres piled in the manner described in
the said former Specification, it is not practicable to carry on the manufacture
of white lead in an efficient manner or on a commercial scale. If such threads or
fibres are piled to a height of fifty millimetres, the charge on each tray, when only
partially corroded, sinks and thus closes or contracts the spaces or interstices
through which the corroding vapours and gases permeate, so that the said vapours
and gases can no longer reach the lower portions of the charge, and consequently
the said charge is imperfectly or incompletely corroded, and the product contains
a large quantity of metallic or uncorroded lead. I have found, moreover, that the
proper height of the pile for such fine threads or fibres, to ensure efficient corrosion,
is about three-eighths of an inch or about nine or ten millimetres. It is obvious,
however, that the manufacture of white lead with such fine lead fibres piled to this
height, would be the reverse of economical, by reason of the immense quantity of
trays required for such manufacture on a large scale.
I have further discovered, since the filing of my said former Specification, that
other directions given therein are inaccurate as will be seen from the process
hereinafter described, and hence the process as described in the said Specification
is impracticable.
Now, by my numerous practical experiments, I have ascertained that, in order
to effect the uniform and complete corrosion of the entire charge of lead, and to
obtain a product containing the desired percentage of the pigment compound, the
process must comprise certain essential steps or stages, and certain conditions must
be fulfilled, that is to say :--In the process of corrosion, it is of very great
importance, in the first instance, that the strips or cuttings of metallic lead should
be of such dimensions and piled in such a manner that the mass or pile will
retain its shape, the strips or cuttings not yielding under their own weight, until
the entire charge on the tray is completely corroded; and, to ensure this result, the
dimensions of the lead strips or cuttings and the height of the pile should bear
the special relation to each other, and to the quality of the lead to be treated,
hereinafter described. It is also very important, in order to produce a really good
and durable pigment, that the periods during which the charge subjected to the
action of the acid vapour, steam and atmospheric air should be very short compared
with the periods during which the said charge is subjected to the action of the
carbonic acid gas; also that the relative duration of these periods and the relative
proportions of the acid vapour, steam and air should be properly regulated or
determined according to the actions observed to be taking place from time to time
in the corroding chambers. It is, moreover, of great importance that the acid:
vapour, steam and air should be applied at intervals to the charge on each of the
trays either locally or generally as required and the strength or concentration of
the acid be varied, according to the progress of the corrosion in different parts of
the said charge. And it is essential to the satisfactory working of the process and

page_text: the uniform corrosion of the charge, that the corrosion should be facilitated by
sprinkling or showering upon the said charge at suitable intervals a spray of basic
solution or basic cream, and this basic cream, like the acid vapour, steam and air,
should be applied either locally or generally and should be of greater or less
strength or concentration according to the activity or want of activity of the
corrosion in the various parts of the charge. The application of the acid vapour
and of the basic cream either locally or generally according to the state of the
charge from time to time, is necessary by reason of the tendency of the corrosion to
become partial or local and frequently to cease altogether in portions of the charge,
which tendency has evidently been overlooked by previous inventors.
Now I have devised an improved process of manufacturing white lead, by which
the conditions above mentioned are all fulfilled, and by which I am enabled to pro-
duce white lead of a greatly superior quality to that hitherto manufactured, with
economy of acid and at a much lower cost than has heretofore been practicable.
In carrying my invention into practice, I proceed as follows, riz. :-I first
produce strips, ribbons or cuttings of lead of any suitable length and of a breadth
and thickness varying to some extent according to the character of the metal to be
treated, that is to say, according to the tenacity and hardness of such metal; but
these lead strips, ribbons, or cuttings are made of such breadth and thickness as to
be capable, when openly entangled and piled as hereinafter described, of retaining
their shape and supporting their own weight throughout the entire corrosion, and
thus maintaining the requisite clear ways or passages for the corroding vapours and
gases, without collapsing or sinking, until the corrosion of the entire bulk of the
charge has been completed. The breadth and thickness of the lead strips or
cuttings should, moreover, be such as to permit the use of a mass or pile of the
same of considerable height, say about three inches high, on each corrosion-tray,
so that a large quantity of lead can be treated at one time within a comparatively
limited space.
In making white lead from metallic lead of the quality usually employed for the
purpose, I make the strips, ribbons or cuttings for a pile of three inches high,
about one-twelfth of an inch or one-tenth of an inch in breadth, and of a mean
thickness of about one-forticth or one-fiftieth of an inch. As, however, the strength
of the strips or cuttings requires to be varied, in some measure, according to the
composition or character of the metal to be treated, I take a sample of this metal
in the form of strips or cuttings of about the dimensions above stated, and subject
these strips or cuttings to a practical test by the process hereinafter described, to
ascertain whether it is desirable to use stronger or weaker strips or cuttings. I
thus find out the most advantageous dimensions of the said strips or cuttings.
These dimensions will, moreover, be somewhat varied according to the desired
height of the mass or pile on the corrosion-trays or grids, the strength of the strips
or cuttings being slightly increased for a pile of greater height and slightly
diminished for a pile of less height.
I pile the said strips, ribbons or cuttings of lead in a tangled mass on corrosion-
trays or grids made with netting (preferably painted as hereinafter appears) of
about one-fourth of an inch mesh, as nearly as possible in such a manner that the
spaces or ways for the corrosion vapours or gases between adjacent pieces of the
said strips or cuttings will be of uniform area throughout the mass or pile of
the strips or cuttings, such area being (as hereinafter described) that which will
the most effectually ensure the proper action of the corrosion vapours upon, and the
thorough corrosion of the said strips, ribbons, or cuttings.
I have found that this piling of the strips or cuttings is best accomplished by
taking the spiral or curled cuttings produced by a self-acting lathe or similar
cutting tool, in the loosely piled and entangled form in which they are deposited as
they fall from the lathe or other cutting tool, and slightly squeezing or pressing
the entangled cuttings together, or drawing them apart if necessary, until, on
looking through the mass, the collective area of the spaces between the strips or
cuttings appears to be about equal to the collective area of the strips or cuttings

page_text: themselves, and the vapour ways are of approximately uniform area throughout the
mass. This arrangement of the strips or cuttings must be very carefully carried
out, because any outstanding or projecting strip will, by reason of the fuller
access thereto of the corrosion vapours, be corroded too rapidly and will fall and
block the vapour ways below it. Moreover, if the strips are too closely packed at
any part of the charge, the corrosion of this part will be retarded until too great a
proportion of the charge is, by the application of too much acid vapour, basic cream
and steam, brought to the state of coarse crystallization, thus diminishing the
covering power and opacity of the product.
My object in arranging the strips or cuttings in this particular manner, is, there
fore, to ensure free and uniform or regular access of the corrosion vapours and
gases to all parts of the strips or cuttings throughout the charge, so that the said
vapours and gases will act uniformly upon all of the said strips or cuttings. I
employ weaker acid vapours than are used in the processes hitherto described by
previous inventors, but notwithstanding this, the said vapours perform their function
in my process more advantageously than heretofore, and moreover, by reason of
the use of the weak acid as hereinafter described, the production of large quantities
of the higher qualities of white lead can be effected by my process in a shorter
period and with a less expenditure of acid than is practicable with the processes
hitherto adopted.
I treat the lead strips or cuttings prepared and arranged as above described,
by means of basic cream, that is to say, by means of basic compounds of suitable
hydrates, such as white or other lead oxides, digested to the consistency of thin
cream in weak pyroligneous, acetic or other suitable acid and water. For this
purpose, I prefer to dip or immerse the strips or cuttings in the basic cream or
compound, and to allow them to drain before placing them on the corrosion-trays or
grids. Care must be taken, however, that all the metal of the charge is properly
covered with the basic cream.
I make the corrosion-trays with suitable frames, preferably of painted wood,
and with a bottom or grid of cotton-netting, preferably painted to prevent
decomposition thereof by the acid, having meshes of about one quarter of an inch
across, so as to prevent the dropping of corroded particles from either tray into
the tray beneath, whilst permitting the circulation of the corrosion vapours and
gases through the bottom of the trays.
I so construct the said corrosion-trays or grids and arrange the same in the
corroding chamber that the ways or passages between them for the corrosion
vapours and gases will be of a depth equal, or approximately equal, to that of the
piles on the trays or grids, say about three inches. Moreover I make the corroding
chamber and the said trays of such relative dimensions that there will be sufficient
space around and between adjacent trays and between the trays and the walls
of the corroding chamber, to permit the free circulation of the corrosion-vapours
and gases by convection as hereinafter described. The width of this space I
find should be somewhat greater than the depth of the vapour ways or spaces
between two adjacent trays.
Having placed in the corroding chamber one above another, the trays or grids
with the lead strips or cuttings piled thereon as above described, I close the said
chamber and inject into the same over each of the entire series of trays, a jet or
spray of acid vapour, steam and air in proportions regulated as hereinafter
described according to the requirements of the charge. After subjecting the
charge to this treatment for about one hour (more or less as the appearances of the
charge may show it requires), I admit to the said chamber, carbonic acid in
the form of furnace-gases, purified on their way to the said chamber by means of
chlorine, from sulphur and other deleterious compounds. I allow the carbonic acid
gas to diffuse in and through the corroding chamber, and, at regular intervals, say
during about one hour (more or less) out of every twenty-four hours, I subject the
charge first to the action of a shower or spray of the aforesaid basic cream and then
to the action of the acid vapour, steam and air as above mentioned. I can, if

page_text: desired, shut off the carbonic acid during the treatment with the acid vapour,
steam and air and with the basic cream, but I prefer that the diffusion of the
carbonic acid gas should be maintained continuously.
Should any part of the charge be found to be too wet, the supply of steam must,
by means of the jet controlling the same, be reduced until such part of the charge
is sufficiently dried. If, on the other hand, any part of the charge should become
too dry, more steam and less air must be applied thereto, with commensurately more
concentrated basic cream and acid vapour.
Should any parts of the charge exhibit signs of too gross and coarse a crystal-
lization, the effect is counteracted or alleviated by increasing the length of the
periods between the applications of the acid vapour, steam and air, and of the
basic cream, or by diminishing the strength or concentration of the acid and of
the basic cream, while continuing the supply of carbonic acid gas, as may be
deemed desirable.
The acid vapours which I use are those of pyroligneous, acetic, nitric or
hydrochloric acid in quantity and concentration such as the character of the
lead to be treated may require. I prefer to introduce the acid vapour, steam
and air and to regulate the relative proportions thereof by means of the apparatus
hereinafter described. These operations can, however, be performed by other
Suitable means.
The carbonic acid gas should not be forced into the corroding chamber so as to
cause a current of such gas to flow through the said chamber; I, therefore, simply
allow the gas to diffuse slowly in the said chamber through the ways or passages
between and around the trays and between the lead strips or cuttings. To produce
the best results, the carbonic acid gas must be evenly distributed so that it will
come in contact with the charge uniformly throughout the corroding chamber. It
is for this purpose that I provide as hereinafter described for permitting a slow
continuous diffusion of the said gases within this chamber.
It is of great importance in the manufacture of white lead, that the corrosion should
be carried on uniformly throughout the entire charge during the whole of the time
occupied by the process. Usually it will be found that the corrosive action goes on un-
equally in different trays or in different parts of the same tray. To avoid or counteract
this unequal corrosive action, I inspect the charge at suitable intervals and, when I find
that the corrosion has stopped or is not going on with sufficient rapidity in
any part
or parts of the charge, I treat the said charge locally where required with a shower
or spray of the aforesaid basic solution or basic cream more or less diluted by water
according to the appearance of the charge. I prefer to apply this basic cream by a
syringe or by means of the apparatus hereinafter described. And I apply the acid
vapour, steam and air to the charge at intervals as above specified, either locally or
generally, having regard to the rapidity or activity of the corrosion in the various
parts of the charge, the strength or concentration of the acid vapour being
increased or diminished according to the appearance of the charge, that is to say,
I apply more of the acid vapour, steam and air and of the basic cream to those
parts of the charge where the corrosive action has ceased or is not going on
satisfactorily, than to such parts of the charge where the corrosion is progressing
favourably. And, on the other hand, should there be signs of coarse crystallization
in any parts of the charge, I withhold the application of the acid vapour, steam and
air and of the basic cream or I apply very weak basic cream to these parts until the
corrosion again becomes uniform throughout the charge by the continued action of
the carbonic acid gas.
The general directions to be followed, in order to control the chemical reactions
and ensure uniformity of the corrosion throughout the entire charge, may be
briefly stated as follows, viz.:-Those parts of the charge which are observed to be
too dry, should be treated more frequently with more or less strengthened acid
vapours mixed with a larger proportion of steam and less air, or, if the corrosion
has stopped, should have more basic cream applied to them. Those portions which
appear too wet, should be treated with less and weaker acid vapour together with

page_text: less steam and more air, or should have very weak basic cream applied to them for
a suitable period.
Should the growth of crystallization be found to be going on too rapidly, the
length of the intervals between the applications of the basic cream and acid
vapour, steam and air should be increased and less steam introduced with weaker
acid vapour, the basic cream being withheld, if deemed necessary. If, on the other
hand, the corrosiou should cease and the charge become too dry, the length of
these intervals should be diminished and the quantity and strength of the basic
cream applied should be increased in addition to strengthening the acid employed.
Should the already corroded particles be found to be dissolving, the quantity of
basic cream applied should be diminished or the application of such cream should
be stopped for a suitable period.
When necessary for drying purposes; for instance, when the charge is found to
be "sweating," that is to say, when the charge appears to be suddenly throwing off
water of hydration, and becomes dripping wet throughout, the supply of additional
quantities of air to the charge may be provided for, by leaving the corroding
chamber open for a suitable period. The application of basic cream to the charge
at intervals either locally or generally as required, and of varying strength or con-
centration according to the state of the charge or of different portions thereof, is
essential to the satisfactory working of the process, because in time the basic cream
once applied is liable to become decomposed.
The temperature in the corroding chamber is raised above the atmospheric
temperature by the heat of the steam and acid vapour introduced as above specified,
thus ensuring the proper diffusion by convection of the carbonic acid gas and other
vapours as the same cool during the interval preceding the next application of the
acid vapour and steam.
The temperature in the corroding chamber should be kept as low as is practically
consistent with the maintenance of the proper diffusion of the carbonic acid gas.
This temperature will vary with the atmospheric temperature, and need not be more
than thirty degrees above the atmospheric temperature. It is desirable, however,
that the temperature in the corroding chamber should not at any time be raised
above say 90 degrees Fahrenheit, because of the tendency of the excessive heat to
cause the growth of the transparent crystals hereinafter referred to.
The complete corrosion of the lead according to my process, for an ordinary
trade sample, should be effected in about from nine to thirteen weeks. The time
occupied will vary according to the strength of the corrosion vapours employed,
and, to some extent, according to the quality of the metallic lead. By using
weaker vapours and effecting the corrosion more slowly than above described,
I can produce very much higher grades or qualities of the pigment by my improved
process.
Before treating metallic lead on a commercial scale according to my process, I
test a sample of the lead in the laboratory to ascertain the required strength and
proportions of the corroding agents to be employed and the periods during which
such agents should be applied, or the intervals which should elapse between the
successive applications of the acid vapour, steam and air and of the basic cream,
and to find out the proper strength or concentration of the acid vapour and basic
cream. With some of the cheaper qualities of metallic lead, the application of
these agents will require to be repeated at intervals of about from eight to ten
hours and stronger or more concentrated acid and basic cream employed. With
some of the better qualities of metallic lead, it will suffice to apply these agents
once in every thirty or forty hours, or even at longer intervals, or weaker or less
concentrated acid vapour and basic cream may be employed.
In the accompanying drawings:-
Figure 1 is a side elevation, partly in vertical section, showing one of the
corroding chambers aud means for supplying the same with the corroding agents.
Figure 2 is a plan, drawn to an enlarged scale, of one of the corroding trays or
grids made with painted netting as hereinbefore described.

page_text: Figure 3 is a vertical section, drawn to a still further enlarged scale, showing a
portion of one of the said trays with a charge of lead strips or cuttings piled thereon
as above set forth.
Figure 4 is a sectional elevation, also drawn to an enlarged scale, showing a
convenient and advantageous form of apparatus for the mixing of the acid vapour,
steam and air and the introduction of the same into the corroding chambers, and
Figure 5 is a sectional elevation of a convenient and advantageous form of
apparatus for applying a shower or spray of basic cream to the charge to be
corroded.
Like letters indicate corresponding parts throughout the drawings.
A is the corroding chamber; B, B are the trays or grids arranged one above
another therein, two vertical series of these trays or grids being shown in Figure 1
of the drawings. The sides of the chamber A are provided with holes A¹ for
the introduction of corroding agents as hereinafter described. These holes are
closed by suitable plugs C, which can be readily removed and replaced as required.
D is a furnace shaft of any suitable description, connected by a pipe E with a
vortex-chamber F, and provided with dampers or valves D', D2, whereby the flow
of the gases or products of combustion may be controlled so as to cause the same
to descend through the pipe E by reason of their increased density on cooling, or to
allow them to escape into the atmosphere. The vortex-chamber F is connected by
a pipe G with the lower end of a coke-tower H, containing damped coke. The
upper end of this tower is connected by a pipe J with the corroding chamber A.
The chamber F is provided with a lead-lined tray or drawer K, in which are placed
suitable substances for generating chlorine, such, for instance, as mixtures of
manganese, common salt and sulphuric acid, whereby a sufficient excess of chlorine
is mixed with the furnace-gases in the chamber F and coke-tower H to purify such
gases from sulphur and other deleterious or discolouring compounds, before the said
gases pass into the chamber A. The chamber A is provided at the top with an
outlet pipe L for the escape of air and of the corroding vapours and gases. The
sides of the said chamber A are either so made that they can be readily removed
and replaced, or they are provided with suitable doors which can be opened for the
inspection of the charge or to permit the access of air to the said charge, if necessary,
for the purpose of drying the same. M is an apparatus hereinafter described for
the introduction of acid vapour, steam and air into the chamber A.
This apparatus is more clearly shown in Figure 4. It is supported upon a suitable
truck a so that it may be readily shifted from place to place as required. The said
apparatus comprises a vessel or tank 6 for containing hot water, in which is partially
immersed a closed vessel or receptacle c for the acetic, hydrochloric or other acid to be.
vaporized, the strength of which acid is varied from time to time as the charge may
require. The receptacle is provided with a stirrer or agitator d and is connected by
a pipe e with an injector f for forcing steam, either alone or mixed with air, into the
said receptacle c beneath the level of the liquid therein through a fine rose. This
injector is connected by a pipe g with a separator to which steam is supplied
through a flexible pipe from a suitable steam-pipe or main. The water of con-
densation from the separator his conducted through a pipe into the tank b,
wherein its heat is utilized for evaporating the acid in the receptacle c; and an
overflow pipe is provided for the escape of the superfluous water from the said
tank b. To the upper part of the receptacle c is connected a flexible pipe m
provided with a nozzle m'adapted to be inserted through the holes A¹ in the side or
wall of the corroding chamber A. for the purpose of introducing the acid vapour,
steam and air into the said chamber when and where required. Suitable cocks or
valves n, n', n² are provided for controlling the working of the apparatus. The
injector f is, moreover, provided with a screw-spindle for regulating the flow of
steam through the same, and the nozzle f of the injector is made adjustable for the
purpose of regulating or controlling the induction of air into the receptacle c by
means of the said injector. The apparatus is also furnished with a safety-valve p
and pressure-gauge q.

page_text: Referring to Figure 5, N is a vessel or receptacle for containing any suitable
basic cream or compound, which is introduced into it through a funnel P and
cock P¹. The vessel N is provided with a stirrer or agitator Q, and with a pump R
for forcing air into it under pressure. The said stirrer and pump are both operated
by means of a pivoted lever or handle S. A flexible pipe T is connected at one
end to the lower part of the vessel N, and is provided at its other end with a
nozzle T'adapted to be inserted in the holes A¹ in the side or wall of the corroding
chamber A for the purpose of introducing the basic cream into the same when and
where required.
ני
By means of this apparatus, the basic cream can be very readily applied in a
shower or spray to the charge on each tray or grid in the corroding chamber, either
locally or generally as may be required, and the strength or concentration of the
basic cream can be easily varied from time to time according to the requirements of
the charge.
The differences between my white lead and that made by the processes hitherto
adopted, can be readily distinguished by subjecting the same to microscopical
examinations; by the application of the paint to a surface by means of a brush
handled by an experienced painter; and also by grinding in oil, mixtures of the white
lead with measured quantities of black or tinted pigment, for comparison in respect of
shade with any sample, the lighter shade being in degree the pigment of greater
covering power and opacity.
White lead consists of varying proportions (mechanical mixtures) of flat long or
tabular prismatic crystals which are transparent or semi-transparent, and of
efflorescent rounded opaque particles of a peculiarly brilliant whiteness distributed
among the said crystals. The covering power of the compound depends upon the
percentage of these opaque rounded particles. And I have found that, under
certain conditions, which sometimes occur in the manufacture of white lead as
hitherto carried on, this opaque product is re-converted into the transparent crystals
above mentioned, thus diminishing the covering power of the compound and causing
a great waste of acid.
Now by my process I produce a compound containing a larger percentage than
the white lead heretofore made, of the aforesaid opaque rounded particles, so that
the covering power of my improved compound and its capacity to effect the
solidification or drying and hardening of the oil are greatly increased as compared
with white lead as heretofore manufactured, and my improved compound is, by
reason of the small proportion of the flat tabular prismatic crystals (as herein-
before appears) and also by reason of the almost entire absence of metallic lead, free
from liability to further corrosion in the atmosphere.
My improved white lead has, for the reasons just mentioned, more opacity and
covering power than ordinary white lead, and has a greater power of solidifying or
drying and hardening the oil.
By my invention, moreover, I am enabled to advantageously utilize in the
manufacture of white lead, the cheaper qualities of metallic lead, the treatment of
which by the processes hitherto adopted has been found impracticable by reason of
the discolourations which are imparted to the product.
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 1
claim is :-
:-
First. The improved process of manufacturing white lead, consisting in first
forming curled, twisted or tangled strips, ribbons or cuttings of metallic lead of
dimensions proportionate to the desired height of the pile thereof and to the quality
of the metal as above described, dipping or immersing the said strips or cuttings in
basic cream and, after draining the same, piling them on trays or grids so as to
leave suitable vapour ways as above described, and then inserting the charge thus
prepared, in the corroding or converting chamber, and repeatedly subjecting it
therein alternately to the action of acid vapour mixed with steam and atmospheric

page_text: air and applied locally or generally to the charge on each tray or grid, and to the
action of purified carbonic acid gas caused to diffuse slowly in and through the said
chamber, and applying to the charge from time to time and locally or generally
as required a shower or spray of basic cream, substantially as hereinbefore
described.
Second. In the manufacture of white lead, the formation and piling of the curled,
twisted or tangled strips or cuttings of metallic lead in the manner herein before
described, so that there are no outstanding or projecting strips or cuttings and the
dimensions of the lead strips or cuttings are relatively proportioned to the height of
the pile as above specified, and, whilst proper vapour ways through the charge are
obtained, the piled cuttings have the necessary strength to retain their shape until
completely corroded, substantially as above set forth.
Third. In the manufacture of white lead, subjecting the charge of lead strips or
cuttings proportioned and piled as hereinbefore described, alternately to the action
of acid vapour mixed with steam and atmospheric air, and of basic cream, and to the
action of carbonic acid, applied in the manner and approximately for the periods
above described, such periods being varied according to the quality of the metal to
be treated and according to the state of the charge and the progress of the corrosion
at intervals throughout the process, substantially as above set forth.
Fourth. In the manufacture of white lead, the treatment of a charge of lead strips
or cuttings proportioned and piled as herein before described, with a spray of basic
solution or basic cream at suitable intervals and locally or generally as required,
having regard to the progress of the corrosion in different portions of the charge, as
above set forth.
Fifth. In the manufacture of white lead, the treatment of the charge in the
corroding chamber with acid vapours and basic cream of varying degrees of con-
centration or strength according to the irregularities observed in the corrosion of
the said charge, substantially as hereinbefore described.
T
19L 1 of Au 1900
D. YOUNG & CO.,
11 & 12, Southampton Buildings, London, W.C., Agents for the Applicant.