IMPROVEMENTS IN THE MANUFACTURE OF A CERTAIN. PIGMENT
Year: 1849

page_text: TO ALL TO WHOM THESE PRESENTS SHALL COME, I, CHARLES
BARLOW, of Chancery Lane, London, Esquire, send greeting.
WHEREAS Her present most Excellent Majesty Queen Victoria, by Her
Letters Patent, under the Great Seal of the United Kingdom of Great Britain
and Ireland, bearing date. at Westminster, the Twenty-ninth day of November,
in the thirteenth year of. Her reign, did give and grant unto me, the said Charles
Barlow, my exors, admors, and assigns, Her special licence, full power, sole
privilége and authority, that I, the said. Charles Barlow, my exors, admors, and
assigns; and such other persons as I, the said Charles Barlow, my exors,
admors, and assigns, should at any time agree with; and, no others, from-time,
to time and at all times thereafter during the term of years therein mentioned,
should and lawfully might make,. use, exercise, and vend, within that part of
Her Majesty's. United Kingdom of Great Britain. and Ireland called, England,
Her Dominion of Wales, and Town of Berwick-upon-Tweed, an Invention for
"IMPROVEMENTS IN THE MANUFACTURE OF A CERTAIN. PIGMENT;" in which said
Letters Patent there is contained a proviso, requiring that I, the said Charles
Barlow, shall particularly describe and ascertain the nature of the said Inven-
tion, and in what manner the same is to be performed, by an instrument in
writing under my hand and seal, to be enrolled in Her Majesty's High Court
of Chancery within six calender months next and immediately after the date
of the said in part recited Letters Patent, as, reference being thereunto bad,
will more fully and at large appear.

page_text: NOW KNOW YE, that in compliance with the said proviso, I, the said
Charles Barlow, do hereby declare the nature of the said Invention, and the
manner in which the same is to be performed, to be particularly described
and ascertained in and by this present instrument in writing, reference being
had to the Drawings hereunto annexed, that is to say:-
These improvements have reference to the manufacture of that pigment
commonly known as "zinc white," and have for their object, firstly, the
obtaining of a larger product of the pigment from a given quantity of metallic
zine; and, secondly, the saving of fuel in the process of manufacture; and they
may be more easily understood by classifying them under five distinct heads.
The first part relates to the means employed for preventing as nearly as
possible the formation of imperfect oxide of zinc in the crucible or tube.
The second part relates to the mode of converting imperfect oxide into pure
zinc white without reducing such imperfect oxide of zinc to the metallic
state.
The third part relates to the application of carbonic oxide gas in con-
junction with steam, or of common coal gas in the manufacture of zinc
white.
The fourth part relates to the peculiar arrangement or construction of what
is called the "receiver" or chamber, in which the zinc white is collected.
And the fifth part relates to the re-heating of the zinc white, in order to
drive therefrom any arsenic which may be mixed with it.
The process of the manufacture of zinc white usually followed in this
country consists chiefly in burning the vapour of heated zinc by mixing there-
with either cold or hot air as the vapour arises from the metal, and then
collecting the oxide formed during the combustion in receivers of various
constructions; but it is well known that in the ordinary methods there is much
difficulty in obtaining the pigment of uniform colour and quality, owing to the
production of imperfect oxide, or, in other words, the admixture of particles of
metallic zinc oxide and sub-oxide of zinc in the crucible or tube. This
imperfect pigment is of course less valuable in commerce than the pure zinc
white, and its formation obliges the manufacturer to stop the process in order
to clean the crucibles or tubes; it is also a common practice for the manu-
facturer to reduce the impure oxide to the metallic state, and then to
re-evaporate it, a process which enhances the cost of the manufacture,
inasmuch as a considerable quantity of fuel is required for that purpose.
I shall now describe the improved process of manufacture with crucible
furnaces, making reference to the Drawings annexed. The fires being lighted
in the fireplace A, shewn at Fig. 1, and the crucibles B being raised to a

page_text: bright red heat, charcoal is to be ignited and placed in the furnace C, and
more charcoal added till its depth is about three feet six inches or four feet;
the slide D of the feeding hopper E is then shut, and air blown in through
the pipe F by means of the fan G, till, on trying the gas at the end of the
pipe H (which terminates with a stop-cock for that purpose in the open air),
the gas given off is found to be combustible, and burn with a steady purple
flame; the stop-cock is then closed, and red-hot zinc is poured into the
crucibles B, through the small opening a, by means of a long taper pipe or
funnel. The slides b, b, are then drawn out, by which the air that has been
heated by passing through the hot-air pipe in its passage from the fans G is
admitted into the oxidizing chamber L at c, c; at the same time the cocks d
are opened, and the carbonic oxide gas formed in the furnace C is allowed to
pass either into the crucibles, as represented in Sheet 1, Figs. 1, 2, and 3, at
e, or to issue through small holes in the pipe surrounding the aperture f, in
Figs. 1, 2, 3, and 4, in the crucible cover, as represented in Fig. 4. As the
vapour of the zine rises, that and the gas burn together, and both take oxygen
from the heated air, the zinc being converted into oxide of zinc at the same
time that the carbonic oxide gas is converted into carbonic acid, and these two
in part combine, forming a mixture of oxide and carbonate of zine; but as
atmospheric air contains a large proportion of nitrogen, cyanogen is also
formed in the furnace C, which combines also with a portion of the zinc
vapour forming cyanide of zine, which either passes into the receiver in that
state, or is again decomposed into carbonate of zinc and nitrogen; in either case
a snow-white product is the result. This product is blown together with the
excess of air through the passage M, Fig. 1 and 2, into the receiver N, Fig. 2;
where on its entrance it meets with the steam jet g, Fig. 2, and this, by
damping it, enables the uncombined oxide to unite with the free carbonic
acid in the receiver (formed by the combustion of the carbonic oxide);
and in order to induce this formation of the carbonate the more readily,
I prefer to keep up a pressure of air in the receiver equal to about two
or three inches of water, which is done by adjusting the outlet valves O, O;
Fig. 12, according to the velocity of the fan. The quantity of gas to be
admitted may be judged by the colour of the flame, which should be a
bright green, a blue flame shews that there is too little, and a purple flame
that there is too much gas, the supply of which must be regulated by the
stop-cocks d, shewn at Figs. 1 and 2. When the charcoal furnace requires
replenishing, which may be observed through the sight hole h, which is
covered with talc, the slide D, Fig. 1, is shut, and the hopper E is filled with
charcoal, the cover P is then put on, and the slide drawn out, when the

page_text: charcoal falls into the furnace through F, without allowing any of the gas to
escape; when the ash-pit 2 requires cleaning out, it is only necessary to remove
the cover i for a moment, when the ashes will be immediately expelled by the
wind from the fans. Between the furnace C and the crucible furnaces is
placed the purifier, which; when charcoal is used in C, consists of a series of
wire gauze screens k, Figs. 1 and 5, fitted in a similar manner to the
throttle valves of steam pipes, having external levers attached, as at 1, Figs. 1
and 5; these levers are connected by the bar m, Fig. 1; these screens serve to
keep back any dust that may be blown through the furnace C; and should
they become clogged they may be cleaned in a few seconds by opening the
cover. n, and lifting the handle o sharply into the position shewn by the dotted
lines, when the dust will be shaken from their surfaces by their striking
against each other, and will be blown out at the opening from which the
cover n was removed. It will be perceived by the Drawings, that the gas
from 'the furnace C enters at the lower part of the purifier, and issues near
the top. The front of the oxidizing chamber L, Fig. 1 and 2, is closed by an
iron shutter R, which is luted found when in its place'; in this shutter there
is a small hole:p, and.over this. hole a slide with a corresponding hole glazed
with glass S, which, when drawn up so that the glass is opposite the hole in
the shutter, enables the workman to observe the color of the flame, or by
drawing it up still-higher will enable him to insert a small scraper to remove
any cones." that may have been accidentally formed about the crucible
mouth. Immediately over each crucible is a large opening T; Fig.1 and 2,
through which the crucible is put in its place, or removed in case of fracture
or other necessity for changing; this opening is made air-tight by luting on
the iron 'cover q; and for the facilitating of the renewal or fitting of the
crucible, the 'different branches of the gas pipe have ball and socket joints
fixed in them; as shewn at r, Figs. 1 and 2: As it is found beneficial to keep
the oxidizing chamber as hot as possible, the smoke flue k', Figs. 1 and 2,
should rise from the furnace, and pass along each side of the oxidizing
chamber before it passes into the general or conimon flue; should the heat in.
the furnaces at any time become too intense, it may be. at once lowered by
closing the ash-pit doors in Fig. 1 and 2; or if a crucible should break
while in use, tlie valve V, Fig. 2, should be instantly lowered to prevent any
dust passing into the receiver. Coke' may be employed in the furnace C,
instead of charcoal, but then it will be necessary to pass the gas formed
through a lime purifier to absorb the sulphurous acid formed during its
combustion. When common coal gas is used, the usual apparatus to produce
it is employed, which is well known. In this case no steam jet is necessary,

page_text: as the hydrogen in the coal, gas produces water in sufficient quantity. When
the furnace represented in Figs. 9, 10, and 11, Sheet 2, which I call the
"tube" furnace is employed, the zinc is poured into the bent tubes x, through
the funnels s. (when the tubes are sufficiently heated); these funnels are fixed
in the iron door t; this door is. luted in its place when the furnace is in use,
but is made to be moveable, that the tubes x may be removed when necessary.
The other parts of these furnaces are the same as in the crucible furnaces,
except that the gas enters the space u, in front of the tubes, from the pipes H¹,
Figs. 9 and 10,. thence passes through the tubes a, carrying with it the zinc
vapour, and both burn together on reaching the oxidizing chamber L, Fig. 10,
in, which the heated vapour and gas. meet the hot air from the pipes I',
Figs. 10 and 11. The supply of air is regulated by the throttle valve v,
Figs. 10 and 11, acted on by the handle w, Figs. 9 and 10, the products
then pass onwards through the passage M, Fig. 10, into the receiver N, where
they come in contact with the steam jet g, as before described; the flues K',
Figs. 10 and 11, of this furnace pass out near the crown of the arch Y, Figs.
9,.10, and 11, through four openings. When, either of these furnaces (that
is; the crucible or tube furnace) is used, a series may be built along the wall
of the receiver, then one gas pipe H will supply them all through the branches
H', and one hot-air pipe. I will supply them all with hot air through the
branches I, as shewn in the Drawings, where a series of crucible furnaces is
represented in sections through the lines. a, b, c, d, and e³, f2, in Figs. 1
and 2, and a tube furnace in. Figs. 9, 10, and 11; in section, through the lines,
a, b; and c, d. The furnace C, in which the carbonic oxide is formed,
is made of plate iron,. and is lined; throughout with fire brick; the air pipe I
is also made of plate iron, and is, supported at intervals in the smoke flue by
cross bars of iron. In this process the deoxidizing gas, carbonic oxide, or
common coal gas, whichever may be used, enters the crucible, as represented
in Figs: 1, 2, and 3, or the, tubes, as,shewn in Fig. 10, and remains always in.
contact with the. heated metal, to the total exclusion of atmospheric air, thus
it becomes impossible, that any oxide can (if the supply of gas be properly.
kept up) be formed in the crucible or tube...
The arrangement represented in Fig. 4 accomplishes the same object by
surrounding the aperture of the crucible with the gas, thus shutting out the
atmospheric air; but besides the advantage of preventing the formation of
imperfect oxide of zinc in the crucible or tubes, either of. the above gasses,
when burned as above, forms (by its combination with the oxygen of the
atmosphere) carbonic acid, which unites with the oxide of zinc in its nascent
state, and thus forms carbonate of zinc ;;but as this carbonate is in part again

page_text: decomposed into oxide and carbonic acid by the intense heat, these two sub-
stances are again made to unite in the receiver by means of the small
quantity of moisture produced by the steam jets, or by the combustion of the
hydrogen of the coal gas, when that gas is used, and a slight pressure kept up
by the blowing fans, which is all that is necessary to cause the oxide and
carbonic acid again to recombine, and thus increase the product nearly one-
half in weight.
Should any imperfect oxide of zinc (which I denominate "cones") be
formed about the aperture of the crucibles or tubes, from there being an
insufficient supply of gas at any time, these "cones are to be raked off
through the hole p, and allowed to remain in the oxidizing chamber till there
is sufficient quantity to make it worth collecting; the door or shutter R is
then removed for a short time and the "cones" taken out (the valves V
being closed all the time the shutters are down); the shutter is then again
luted in its place and the valve raised, when the process goes on as before.
The "cones" thus collected, with any other dirty or imperfect oxide that.may
be used, I place in the "completing furnace," for the purpose of re-burning,
and it may be profitable to purchase impure oxide of zinc, for the purpose of
converting it into the pure pigment by this process. This furnace is repre-
sented in sections through the lines c, d, and e, f, in Figs. 6, 7, and 8.
A is the ash-pit; B, the fireplace; C, the straight tubes; D, an iron door;
E, openings opposite to and of the same diameter as the tubes; F, escutcheons
or valves to shut these openings; G, à space between the ends of the tubes,
into which the hot air enters through I, a branch from the. hot-air pipe I;
M is the passage into the receiver; K', the branches of the smoke flue;
K, the general or common smoke flue. The tubes being raised to a bright
red heat a quantity of the imperfect or dirty oxide is placed in them through
the apertures E by means of a semicylindrical scoop, the heated air in its
passage through the tubes into the receiver completes the oxidization of the
zinc, and at the same time converts the vegetable matter that may be mixed
with it into gazeous substances; when the quantity in the tubes is considerable
it will be necessary to rake it over from time to time to expose every part
of it to the action of the air; when, by looking through the aperture E, it is
perceived that the white fumes have ceased, and that no more arise on
disturbing the mass, then this process is finished, and that which remains in
the tubes may be pushed through into the receiver, as it will then consist
of pure oxide, there to be converted, as above described, into carbonate.
The "receiver," Fig. 12, Sheet 3, in which it is represented one-quarter
of a scale of the Figures in Sheets 1 and 2, is an oblong building divided

page_text: into four parts, marked A, A, B, and C; into the part marked C the passages
M from the different furnaces enter through the wall D. In this part of the
receiver there is a false floor or bottom, made of sheet zinc or copper, raised
in the middle at E from the true floor, and slanting downwards each way
as far as F, F; the remainder of this floor from F to G¹ in each direction is
covered by pans or trays a, a, Fig. 12 and 13, made of zinc or copper, with
rims all round, except the ends that pass under the false floor at F, F; here
a falling valve or flap, extending from f to f', cuts off all communication from
the part marked B, and the same is the arrangement on either side of the
raised floor, as shewn in section through the line a', 6', in Fig. 13. The parts
A,.A, are exactly similar, and consist of a series of moveable frames H¹, over
which an open fabric or canvas is tightly stretched. Attached to the bottom
of these frames, on the side nearest the furnaces, is a metal tray b, b, with a
rim all round it, which rests on the floor, and occupies all the spaces between
the one screen and the next, except the first screen on each side I, I, which
are not attached to the trays a, a, Fig. 12. 0, 0, are the two outlet valves,
which may be regulated at will, so as to keep up a pressure of air in all the
parts of A, A, and C, as before described. The frames over which the canvas
is stretched run in groves extending from K to K at top; and through a
slot in the partition L, L, between A, A, and B, any one of the screens,
together with its tray, may be drawn out of the part A into the chamber B,
and there freed from the adhering zinc white.. In order to prevent the escape
into this chamber of the zinc white still floating in the air of the parts A, A,
a direct pipe passes from the fans into the collecting chamber B, thus giving
a slight advantage to this chamber in regard to pressure, by which the air
will rather pass into the parts A, A, than out of A, A, into B; the slots
through which the frames pass, and also the jambs against which the ends
of tray sheet are covered with felt or other similar substance, to make the
joints as air-tight as possible. The manner of working with this receiver
is as follows:-The zinc white entering the part C through M, will in part
fall in C on the slanting part E, F, F, and in the trays a, a, but when any
large quantity has collected on E, F, F, this will also fall into the trays a, a,
which are removed by lifting the flap (f, f,) and drawing either tray to its
full extent; then by letting the flap fall and pushing in the tray the whole
of the contents are pushed out by the flap. Another portion of the zinc white
will pass onward into the ports A, A, and there meeting with the screens will
be gradually precipitated on them, and may be collected from one screen at a
time by drawing it through the slot in L, when the felt will wipe the canvas
as it passes it, and the zinc white will fall into the attached tray, from which

page_text: it may be easily removed. In the chamber B the zinc white may be packed
ready for the market, or reserved for the last part of these improvements,
if necessary.
The last part of these improvements consists in heating the zinc white
which is found to contain arsenic to about 400° Faht, by which the arsenic
is sublimed, and may be collected; for this purpose it is put into earthern
vessels, and then placed in an oven, from. the top of which a pipe carries off
the arsenical vapour into any cold receiver, where. the vapour will condense
in a solid form..
Further description is unnecessary with respect to this part, as the process
will be readily understood by any one acquainted with the manufacture.
Having now described the nature of the said Invention, and in what manner
the same is to be performed, I desire to be understood that I do not confine
myself to the precise details herein-before described, because I am aware that
many minor modifications may.be. made both with respect to the mode of
operating and to the construction of the apparatus employed, and I make no
claim to the production of any of the cases herein-before described; but what
I claim is,
Firstly, the application of deoxydising gas containing carbon in the manu-
facture of zinc white.
Secondly, I claim the converting of impure oxide of zinc into. pure zinc
white, as herein-before described.
Thirdly, I claim the use of a.receiver having moveable screens in the said
manufacture, as herein-before described.
Fourthly, I claim the subliming of the arsenic which may be contained in
zinc white by heating, in the manner herein-before described.
In witness whereof, I, the said Charles Barlow, have hereunto set my
hand and seal, the Twenty-ninth day of May, One thousand eight
hundred and fifty.
1.
CHARLES
(L.S.) BARLOW.
CHARLES JOHNS.
Signed, sealed, and delivered in the presence of
29/5/50.
Enrolled the Twenty-ninth day of May, in the year of our Lord One