REDS.
Though the red pigments are an important class, they are not numerous,
and, with the exception of a few lakes, they are drawn from the mineral
kingdom. The most useful are compounds of the several metals, iron,
lead, and mercury.
ANTIMONY VERMILION.--This useful pigment is prepared by
several methods, as follows:--
(1) One of the earliest successful processes was that introduced by
Mathieu Plessy, which gives a scarlet product. He obtains the pigment,
a modified sulphide of antimony, by decomposition of hyposulphite of
soda in the presence of chloride of antimony. The two solutions of
hyposulphite of soda and chloride of antimony, each at 25° B., being
prepared, the next step is to pour into a stoneware vessel 4 gals. of
the antimony chloride solution, 6 gals. of water, and 10 gals. of soda
hyposulphite solutions. The precipitate caused by the water is rapidly
dissolved in the cold by the hyposulphite. The stoneware vessel is
then placed in a hot water bath, and the temperature of the contents
is thus gradually raised. At about 86° F. the precipitation of the
sulphide commences, showing orange yellow at first, but becoming darker
subsequently. When the temperature has reached 130° F., the vessel is
removed from the water bath, and the deposition of the precipitate
proceeds rapidly. The supernatant liquor is siphoned off, and the
solid residue is washed first with water acidulated by adding to it
one fifteenth of its bulk of hydrochloric acid, and then with clean
water. Finally the residue is collected on a filter, and dried. It is
exceedingly brilliant while wet, but loses a portion of its brightness
when dried.
Provision must be made for disposing of the sulphurous oxide gas driven
off during the process of manufacture.
(2) Kopp found certain disadvantages in working by the above method,
and adopted instead the reaction of antimony chloride upon a dilute
solution of hyposulphite of lime.
Experiencing much difficulty in the decomposition of antimony sulphide
by hydrochloric acid on an industrial scale, he experimented on
roasting the sulphide at a moderate temperature in contact with air
and steam, whereby most of the antimony sulphide is converted into
oxide, while the sulphurous acid driven off is utilised for making
the hyposulphite of lime. This proved a most successful plan, and
the resulting antimony oxide is readily dissolved by commercial
hydrochloric acid.
During the oxidation of the antimony sulphide, a certain proportion
of antimonious acid may be produced. This is but slightly soluble in
hydrochloric acid. It may be collected, however, by saving the residues
from the treatment by hydrochloric acid, and washing them with chloride
or hyposulphite of lime, which will dissolve the adherent antimony
chloride; they are then dried, and melted with a little antimony
sulphide and quicklime, so as to transform the whole into antimony
green, the quicklime having the effect of decomposing any small residue
of antimony chloride.
The preparation of the hyposulphite of lime is cheaply effected by the
action of sulphurous acid on sulphides of lime, the sulphurous acid
being derived either from the roasting of the antimony sulphide, or
from pyrites or brimstone in the usual way.
Calcium polysulphide is prepared by boiling finely powdered sulphur and
newly slaked lime in water. Certain advantages arise from the addition
to this solution of a little powdered calcium oxysulphide, or some
quicklime.
In the reaction of sulphurous acid on calcium sulphide and oxysulphide,
sulphur is set free and forms a sulphite of lime, which, in the
presence of sulphur and undecomposed sulphide, is soon transformed into
hyposulphite, the reaction being facilitated by the rise of temperature
which takes place in the apparatus.
As soon as the liquor has become slightly acid, it is drawn off into
a large settling tank. If, after agitating for some time, the liquor
has not become neutralised by the undecomposed calcium oxysulphide
contained in it, this is brought about by addition of a little calcium
sulphide, and is recognisable by the appearance of a black precipitate
of sulphide of iron. After due settlement, the clear liquor is
decanted, and forms a solution of nearly pure hyposulphite of lime.
The production of antimony vermilion is effected from the foregoing
solutions of antimony chloride and hyposulphite of lime, in apparatus
consisting simply of a series of wooden tanks raised conveniently above
the floor, holding about 500 gals. each, and provided with steam coils
for heating their contents.
Sufficient hyposulphite of lime solution is run into the tanks to fill
about seven-eighths of their depth; and then into the first tank is
poured the chloride of antimony solution, in quantities of a few pints
at a time. A white precipitate is formed, and rapidly dissolves at
first; when it is slow in going into solution, even though stirred,
the addition of antimony chloride should be stopped, as an excess of
hyposulphite of lime is essential. The liquor in the tank must be
perfectly clear and limpid, and should any white precipitate remain it
must be dissolved by making small additions of hyposulphite.
At this stage steam is admitted into the coils, and thereby the
temperature of the solutions is gradually raised to 120° or 140° F., or
even to 160° F., while stirring is unceasingly carried on. The reaction
is soon manifested by the successive colours of the liquor, passing
from straw-yellow to lemon-yellow, orange-yellow, orange, orange-red,
and lastly a very deep and brilliant red. The steam is shut off from
the coil before the desired tint is arrived at, as the acquired heat
and the agitation complete the development of the colour. If the
heating is carried too far, the red gradually passes to a brown and
later to nearly black. With experience, almost any desired shade of red
can be produced.
When the precipitate has attained the required colour, it is allowed to
settle, and the tank is covered. The clear and limpid liquor, having a
strong sulphurous odour, is let out through tap holes at various levels
in the sides of the tanks, and run by wooden gutters or leaden pipes
into a large reservoir holding a quantity of sulphide and oxysulphide
of lime. Here the sulphurous liquor regenerates a certain amount of
hyposulphite of lime.
The antimony chloride solution always contains a large proportion of
chloride of iron, which provides an easy means of guiding the progress
of this latter operation. All the iron remains soluble in the mother
liquors of the antimony sulphide, and as soon as they are brought into
contact with the calcium sulphide, an insoluble black precipitate of
iron sulphide is formed. So long as this remains, the mother liquors
charged with sulphurous acid have not been added in excess; but when
it disappears by conversion into soluble hyposulphite of iron, that is
a sign that the sulphurous solution is in excess. The contents of the
reservoir are then well stirred, and calcium sulphide is introduced if
necessary, until the precipitate of iron sulphide returns and remains.
It is also needful to ensure that a certain proportion of hyposulphite
of iron shall remain in solution. The clear liquor decanted off when
all the precipitate has gone down is a neutral solution of hyposulphite
of lime, containing some calcium chloride and hyposulphite of iron.
Another requisite precaution in this regeneration of hyposulphite of
lime is that no excess of calcium sulphide be left, or it will give an
orange-yellow tint to the vermilion; and if the hyposulphite of lime
solution is alkaline and yellow, sulphurous acid liquor must be run in
till all alkalinity is destroyed.
This regenerated solution of hyposulphite of lime is used like the
first. The mother liquors charged with sulphurous acid are again
neutralised in the large reservoir by new proportions of calcium
sulphide and oxysulphide, until so much calcium chloride is present
that they are useless for the purpose, say after 25 to 30 operations.
The antimony vermilion precipitated on the bottom of the first tank is
received into a conical cloth filter, and the liquor drained off is
passed to the reservoir. The first tank is then washed out with warm
water, which also passes through the filter. The precipitate of red
sulphide cannot be too carefully or completely washed, and finally is
filtered and slowly dried below 140° F.
(3) Wagner’s method of making a scarlet pigment is to dissolve 6 lb. of
tartaric acid and 8 lb. of tartar emetic in 4½ gallons of water at 140°
F., adding a solution of hyposulphite of soda at 40° Tw., and heating
the whole mixture to 180° F., whereby the red pigment is gradually
precipitated. It is collected on a filter, well washed and dried.
(4) The process adopted by Murdoch, in which a solution of antimony
chloride (prepared by dissolving black sulphide of antimony in
hydrochloric acid) is acted on by a current of sulphuretted hydrogen
gas, has disadvantages in the apparatus necessary, in the limited range
of tints which can be produced, and in the almost certain presence of
free sulphur in the finished pigment.
Antimony vermilion forms an exceedingly useful pigment, which can
be prepared in every shade of red, from orange to red-brown. It is
produced in the condition of a very fine powder, requiring no grinding,
and mixes readily with water or oil, especially the latter, and
moreover does not interfere with the drying of the oil. It possesses
great covering powers, and can be made at a low price. It undergoes
no change in strong light and impure air, and is insoluble in water,
alcohol, essential oils, weak acids, ammonia, and alkaline carbonates;
but it is destroyed by high temperatures, strong acids, and caustic
alkalies. It cannot be mixed with other pigments which are intolerant
of sulphur, nor with alkaline vehicles. When pure, it should consist of
nothing but antimony sulphide and a little water; the presence of iron
or lead indicates adulteration.
BARYTA RED.--An orange red may be prepared, according to
Wagner, in the form of a sulpho-antimonite of barium, by calcining in a
clay or graphite crucible at red heat for several hours a mixture of 2
parts of finely powdered barytes, 1 part of native antimony sulphide,
and 1 part of powdered charcoal. The calcined mass is not removed until
the crucible is quite cold, as it is liable to undergo combustion. When
cold, it is boiled in water and filtered. The residue, containing some
undecomposed sulphate and sulphide of barium, is utilised in the next
batch. The pale-yellow filtrate is treated with dilute sulphuric acid,
by which sulphuretted hydrogen is driven off, and an orange precipitate
is thrown down. This is collected, washed on a filter, and dried,
constituting the pigment.
CASSIUS PURPLE.--This costly pigment is a stannate of
protoxide of gold, much used in painting on porcelain and for
miniatures. It is the precipitate which is thrown down when solutions
of gold and tin chlorides are mixed under proper conditions, according
to one of the following methods:--
(1) Buisson prepares three solutions: [_a_] a neutral solution of
protochloride of tin by dissolving 1 part of tin in hydrochloric acid;
[_b_] a solution (bichloride) of 2 parts of granulated tin in an aqua
regia containing 3 parts of nitric to 1 of hydrochloric acid, removing
the excess of acid; [_c_] a neutral solution of 7 parts of gold in an
aqua regia composed of 1 part of nitric and 6 parts of hydrochloric
acid. The gold chloride solution is largely diluted with water, and to
it is added the solution _b_ of bichloride, and finally the solution
_a_ of protochloride is introduced, a drop at a time, until the
desired colour is produced in the precipitate. This last is rapidly
washed by decantation, and finally dried away from the light.
(2) Figuier prepares a gold bichloride solution by dissolving 20
grammes of gold in 100 grammes of an aqua regia containing 4 parts
of hydrochloric to 1 of nitric acid. The solution is evaporated to
dryness in a water bath, and the residue is dissolved in 750 grammes of
water. Into this solution, when duly filtered, pure granulated tin is
introduced, and the whole is left for some days, at the end of which
time all the gold will be in the state of stannate of protoxide; it is
collected on a filter, carefully washed, and gently dried. The residues
contain some gold, and should be preserved for subsequent operations.
CHINESE RED.--One of the many names of the chromate of lead
pigment, described under Derby red, see p. 145.
CHROME ORANGE.--A popular name for the group of yellow-red
pigments consisting essentially of lead chromate, and described under
Lead orange, on p. 147.
CHROME RED.--Another of the synonyms for Derby red, see p. 145.
COBALT PINK.--This costly and permanent artists’ colour is
a combination of oxide of cobalt with magnesia. It is prepared by
treating carbonate of magnesia with a concentrated solution of nitrate
of cobalt; the resulting paste is dried in a stove, calcined in a
porcelain crucible, and finally ground to a fine powder.
COBALT RED.--A very deep-coloured and permanent red pigment
used in oil painting is the arseniate of cobalt, which is found
native in admixture with other substances in cobalt mines, or may be
artificially produced.
The native mineral is treated with boiling nitric acid; the solution
is filtered clear, and small portions of potash are added till all
the iron has been thrown down as arseniate. After this is completed,
the mass is allowed to settle, and the clear liquor is poured off.
On adding further small portions of potash, the cobalt is also
precipitated as arseniate.
To prepare artificial cobalt arseniate, grey cobalt ore (sulph-arsenide
of cobalt), reduced to a powder, is mixed with a little sand and twice
its weight of potash, and fused in a crucible. The slag of mixed
sulphides which is formed is removed, and the remaining white arseniate
of cobalt is pulverised and subjected to another fusion with potash.
The slag is again removed, and the button of pure arsenide of cobalt
remaining is finely powdered and again roasted to effect conversion
into arseniate of cobalt. Lastly, it is ground very fine.
COLCOTHAR.--A fancy name for a kind of iron oxide pigment,
described under oxide reds (see p. 150).
DERBY RED.--As a basic chromate of lead, often known as chrome
red, Derby red is closely allied to chrome yellow, the preparation of
which is described in a subsequent chapter.
It has been asserted that all the chrome reds, from the darkest
cinnabar red to a lustreless minium red, are distinguishable simply
by the size of the crystals composing the powder, as may be easily
determined under the microscope, and that if various chrome reds of
the same hue, but with different intensities of colour, are reduced by
grinding to the same degree of comminution, the several powders will
possess exactly the same degrees of intensity of coloration, though
they lose in brightness. Therefore the conditions which give brilliancy
and intensity of colour are those which favour crystallisation.
On this supposition it is recommended by Riffault to adopt a plan which
dispenses with agitation, and he supports the following method:--
(1) Chrome yellow is precipitated in the usual manner, as described in
a later chapter, without sulphuric acid, and is carefully washed. After
draining, the mass is well stirred, and six or eight equal samples are
drawn from it and put into glass vessels of equal size and thickness
of structure. To each sample is added a different volume of caustic
soda or potash lye, marking about 20° B. For instance, to 5 volumes of
paste are added 2, 2½, 3, 3½, 4, 5, &c., volumes of lye. The different
mixtures are rapidly and thoroughly agitated, but the chemical reaction
is allowed to take place without any disturbance. After examination of
the quality of the products, the relative proportions of pulp and lye
are noted down for the best hues obtained. Too much lye will fail to
deepen the red colour; in fact, Derby red is entirely soluble in an
excess of lye, and forms needle-like crystals holding potash when the
caustic solution has absorbed carbonic acid from the air.
On the industrial scale the operation is conducted in a large tub,
which receives the mixture of pulp and caustic lye in precisely the
proportions found by experiment to give the best results. The changes
in colour soon manifest themselves, and the whole reaction is completed
in about 12 hours. At the end of that time, the lye is drawn off, and
carries with it much of the chromic acid. The precipitated pigment
is carefully washed with pure water once in the tub, and the mass is
gently stirred. The washing is continued in the filters by throwing
water upon the pulp, and in this manner there is less friction between
the crystals, which retain their deep colour. Of course a highly
crystalline dark red cannot possess great covering power.
(2) Prinvalt mixes together 100 lb. of lead carbonate and 30½ lb. of
potash bichromate neutralised with caustic potash, in 50 gallons of
water, leaving them in contact for a couple of days under repeated
agitation. About half an hour’s boiling then suffices to develop the
red colour. After settling, the supernatant liquor is drawn off, and
the precipitated pigment is washed twice with pure water and finally
with acidulated water (1 lb. sulphuric acid in 10 gallons of water),
and dried.
There are several other recipes published which differ in detail from
(2), but they do not demand a lengthy description.
(3) 100 lb. of lead carbonate (white lead) made into a paste with
water, then added to and boiled with a solution of 50 lb. of potash
bichromate and 15 lb. of caustic soda of 77 per cent. Remainder of
process as before.
(4) 4 cwt. of lead monoxide (litharge) and 60 lb. of salt dissolved
in 50 gallons of water, and left with agitation for 4 or 5 days; then
boiled for 2 hours with solution of 150 lb. of potash bichromate.
(5) 100 lb. of lead carbonate (white lead) made into a paste with
water, then added to a solution of 30 lb. of potash bichromate and 12½
lb. of caustic soda at 77 per cent., and boiled.
Derby red possesses great covering power and considerable brilliancy;
but if not very carefully washed it is liable to retain a little
alkali, which renders it unstable. Otherwise, it well resists damp,
strong light, and impure air so long as sulphuretted hydrogen is
absent. Taken altogether it is not one of the best red pigments, and
its consumption is declining.
INDIAN RED.--This is one of the names for the red pigments due
to oxide of iron, and is described under oxide red, p. 150.
LEAD ORANGE.--Equally well known as chrome orange, this
pigment may be regarded as a Derby red in which the reactions have
been curtailed. That is to say, the yellow normal lead chromate
being in excess, the red chromate formed by the action of the alkali
combines with that excess of the yellow salt and forms a yellow-red,
i.e. orange. Obviously, therefore, a great variety of tints can be
produced by altering the proportions of the alkali, and this is further
regulated by the duration of the boiling, while the tint can also be
weakened by admixture of barytes or gypsum. The better kinds of lead
orange are prepared with the aid of caustic potash or soda as the
alkali, while the cheaper sorts depend on lime. The operations are
practically identical with those adopted in the case of Derby red
(see p. 145), the chief differences lying in the proportions of the
ingredients. Thus:--
(1) _Pale._--Add a thin cream made from 10 lb. of quicklime to a
chrome yellow made from 100 lb. of lead acetate, 30 lb. of soda or
potash bichromate, and 21 lb. of soda sulphate. Boil.
(2) _Pale._--Add a thin cream of 10 lb. of quicklime to a chrome
yellow made from 200 lb. of baryta sulphate, 100 lb. of lead
acetate, and 35 lb. of potash bichromate. Boil.
(3) _Deep._--Precipitate a chrome yellow by adding 35 lb. of soda
or potash bichromate to 100 lb. of lead acetate; settle. Draw off
supernatant liquor and admit solution of 9 lb. of caustic soda at
77 per cent.
(4) _Deep._--Add a cream of 10 lb. of quicklime to a chrome yellow
made from 100 lb. of lead acetate, 75 lb. of baryta sulphate, and
35 lb. of potash bichromate. Boil.
In characters the lead oranges resemble Derby red (see p. 145.)
MINIUM.--The important red pigment known as minium or red lead
is composed of two oxides of lead in combination, viz. about 65 per
cent. of protoxide and 35 per cent. of binoxide. In its preparation,
metallic lead is first converted by roasting into protoxide (termed
“massicot,” “dross,” or “casing”) and this protoxide is further
subjected to heat in a reverberatory furnace whereby a portion of it
is changed into binoxide. It is also possible to produce red lead by
the decomposition of the carbonate of lead (white lead) at a high
temperature, but this does not seem to be an industrial process. The
following methods are recognised:--
(1) The practice in France, as carried on near Tours, at the white lead
works using the Thénard process, is to calcine the best metallic lead
in reverberatory furnaces built in the rock. These furnaces are five
in number, with double fireplaces, four being constantly in operation,
dealing with about 4000 lb. at a charge, and using bituminous coal as
fuel. Each furnace is nearly circular in shape and about 11 feet in
diameter, with a fire-place on each side of the hearth. The latter is
constructed of fire-brick containing as little silica as possible,
and is made hollow so as to retain the metallic lead when the heat has
rendered it fluid.
The products of combustion from the side fire-places, having heated
the hearth and its contents, pass through an aperture in front of the
charging door of the hearth, and thence go to furnish heat to an upper
hearth where the conversion of the oxide into red lead takes place.
A period of about 12 hours is occupied in the oxidation of a charge,
which is repeatedly “rabbled.” Even then a considerable amount of the
metallic lead remains unoxidised and is returned to the calciner with
the next charge. Half the oxide is utilised for making white lead, as
described in a later chapter, and the other half is converted into red
lead by the method detailed hereunder.
The crude oxide is pulverised in a small mill and separated from the
unconverted metal. The mill takes the form of a flat circular cast-iron
plate on which rotates a cast-iron muller. Water and an agitating
arrangement are also provided.
As the muller revolves the material undergoes comminution, and the
small particles of oxide as formed are disturbed by the agitator and
kept in suspension in the water, by the overflow of which they are
continuously carried away into settling pits. The residual metallic
lead is not pulverised, and of course never becomes suspended in the
water, consequently it accumulates at the bottom of the mill, whence it
is occasionally withdrawn for re-calcination.
Sufficient oxide having collected in the settling pits, it is
transferred to a shallow pan heated by the waste heat from the furnaces
and is there rendered almost dry. In this state it is put into small
square dishes made of sheet iron, and adapted to hold about 30 lb. each.
A charge consists of a hundred of these dishes, which are placed in
the heated furnaces at the end of each day. The roasting is repeated
several times, and the product is accordingly known as “two fires,”
“three fires,” &c. The material at this stage is lumpy and coarse,
and has to undergo dry pulverisation, the fine particles as they are
produced being drawn off by means of a pneumatic fan, and collected.
(2) What may in contradistinction be called the English method of
making minium does not differ materially from the preceding. The
“drossing” furnace, where the metallic lead is first oxidised, receives
a smaller charge as a rule, and perhaps greater care is given to the
rabbling, and to the regulation of the temperature so that it is only
just above the melting point of the metallic lead, and not sufficient
to fuse the massicot.
Minium or red lead is one of the most important and useful red
pigments, as it mixes well with oil, has good covering power, dries
quickly, and is permanent except in presence of sulphur or sulphides.
ORANGE MINERAL.--The pigment known as orange mineral or
orange lead is simply minium which has been imperfectly calcined.
Consequently it is almost identical with red lead in composition,
qualities, and method of manufacture, the only exception being that,
as the calcination is not carried quite so far, therefore the colour
is not so fully developed, and is an orange rather than a red. As with
minium, practically the only adulterant is iron oxide red, which may be
detected by boiling the pigment to a colourless solution with nitric
acid, when addition of prussiate of potash will give a blue precipitate.
OXIDE REDS.--Under various names--such as Persian red, light
red, Indian red, scarlet red, rouge, colcothar, red oxide, purple
oxide, &c.--many pigments, of which the base is the ferric oxide
Fe_{2}O_{3}, are now made. These vary in shade from a deep scarlet red
to a dark violet. They are obtained both from natural and artificial
sources. Oxide of iron occurs naturally as the mineral hematite, and
some varieties of this are bright enough and soft enough to be used as
pigment when ground up. These are usually nearly pure oxide of iron.
Then the ochres, when calcined, yield red pigments known as light red,
Indian red, &c., and a good many reds are obtained from this source.
The composition of these is variable, being dependent upon that of the
ochres from which they are made, and these, as has already been pointed
out, vary very much. Then, in preparing fuming sulphuric acid from
copperas, oxide of iron which is specially sold as rouge, is obtained.
Colcothar is produced as a residue; this is nearly pure oxide of iron,
and usually has a red colour. In the manufacture of sulphuric acid from
pyrites, a dark violet oxide of iron is left as a residue, and much of
this is used as a pigment under the name of purple oxide. Then a large
quantity of oxide of iron reds are made artificially from waste liquors
obtained in copper refining, galvanising iron, &c. The composition of
the oxide of iron reds, therefore, is very variable.
The whole group of oxide reds is of foremost importance, by reason of
their good colour, covering power, and durability, besides which, being
mostly bye-products of much more important manufactures, their cost is
reasonable.
The methods of preparation of oxide reds vary slightly in detail
according to the material from which they are made, but the general
features of the processes are almost identical and eminently simple.
The principal sources are impure native oxides of iron, such as the
ochres, various waste liquors containing iron salts in solution, and
copperas (protosulphate of iron).
(1) Native oxides. The iron present in the ochres and similar native
earths exists in the form of hydrated oxide, and has a brown red
colour. For many purposes this hue is satisfactory, and the preparation
of such a pigment consists simply in grinding the mineral in a wet
mill, subjecting it to levigation till all grit is removed, and drying.
In order to obtain a brighter red from the native oxides they must be
calcined to effect dehydration. This can be accomplished in the most
rudimentary forms of furnace, and many kinds are in use. The colour
produced depends on the degree and duration of the heat to which the
material is exposed, the shade becoming deeper as the roasting is
prolonged or the temperature increased. As no two samples of ochre are
just alike it is impossible to fix a precise time for the length of the
operation, and therefore it is necessary to repeatedly draw samples in
order to judge of the progress of the dehydration and development of
the colour desired. When the requisite shade is attained, the charge is
drawn and allowed to cool.
(2) Waste Products. The pyrites cinders from sulphuric acid works
afford an abundance of oxide of iron. When the pyrites has contained
no copper, the cinders merely require grinding and levigating, the
iron being present as oxide. But when the pyriteshas been treated
for the recovery of the copper, by a second roasting with salt, the
liquors contain the iron as chloride and sulphate, and lime has to be
added to precipitate the oxide. This last is dried and calcined in the
same manner as the native oxides, and grinding and levigation can be
dispensed with.
The liquors from galvanising works contain acid sulphate of iron (green
copperas) in solution. To correct the acidity, more iron is added in
the form of scrap. Then lime or other alkaline substance is introduced
to throw down the iron as oxide, and this last is filtered out, dried,
and calcined in the usual way.
(3) Copperas. Where beds of common iron pyrites occur, the iron
sulphide is converted into sulphate by exposure to the oxidising
influence of the air. The result is an acid sulphate of iron, which
is leached out and neutralised by addition of more iron in the form
of scrap. The neutral sulphate is crystallised out of the liquor, and
calcined in a muffle furnace, the shade of the ultimate product being
governed by the degree or duration of the roasting. The sulphurous acid
liberated in the roasting is sometimes utilised for making sulphuric
acid, but is more often wasted, because, to be commercially successful,
the sulphuric acid manufacture must be conducted on a large scale,
demanding 100_l._ of capital for every 1_l._ necessary for the copper
and red oxide fabrication.
PERSIAN RED.--A name which is used somewhat indiscriminately
both for Derby red (p. 145) and for oxide red (p. 150).
REALGAR.--The native mineral realgar is a yellow-red
bisulphide of arsenic, often called also ruby of arsenic, or arsenic
orange. It occurs native in very limited quantities in some of the
older rocks, and then only requires to be ground and levigated. But for
painters’ purposes it is prepared artificially by heating a mixture of
sulphur and arsenic in such a way that they are melted in company and
react on each other to form the arsenic sulphide. The heating takes
place in crucibles, and the proportions are two parts by weight of
arsenious acid (white arsenic) to one of flowers of sulphur. When the
reaction has ceased, the contents of the crucible are allowed to cool,
and then reduced to very fine powder.
The pigment is exceedingly poisonous and not remarkably durable,
besides which, it cannot be mixed with any other pigment which is
affected by sulphur.
RED LEAD.--A common name for minium, see p. 148.
ROUGE.--One of the names for a particular shade of the oxide
reds, see p. 150.
VENETIAN RED.--A fancy name for a special shade of oxide red,
see p. 150.
VERMILION.--This old pigment is gradually going out of use;
the newer reds, which are more brilliant in colour and cheaper, are
gradually displacing it, although it is doubtful whether it will ever
go completely out of use. It is the mercuric sulphide HgS. When pure,
it is not attacked by acids or alkalies; only aqua regia, a mixture
of hydrochloric and nitric acids, is capable of dissolving it, when
it forms a clear solution. Heated in the flame of a Bunsen burner,
it is completely volatile, a property possessed by no other pigment
in common use, therefore any adulteration can be readily detected by
simply heating a little vermilion in a crucible; if a known weight is
taken and the residue is weighed, the amount of adulteration can be
ascertained. Vermilion is chiefly adulterated with oxide of iron and
orange lead. From the character of the residue left on heating in a
crucible, the kind of adulteration can be readily ascertained.
(1) The following notes are taken from Christy’s translation of a
brochure on the Imperial Quicksilver Works at Idria, Krain:--
In the oldest times of the existence of the present works, vermilion
was manufactured. In the beginning it was merely pure pulverised
cinnabar ore, then later it was a product made by sublimation from
this substance; and there were formerly other works for vermilion
manufacture than those for quicksilver production. When the Venetians
and Dutch began to produce better wares, the production here sank
steadily.
The researches of Christofoletti, 1681, and of Baron Richtenfels, 1726,
for the improvement of Idrian vermilion, met with as little success as
those of some Venetian women--1740-1741--who had lost their husbands in
the Venetian works and had offered themselves to manufacture vermilion
according to the Venetian method.
After Hacquet had strongly urged the manufacture of vermilion,
Oberhüttenmeister Ignaz v. Passetzky succeeded, with the Dutchman
Gussig assisting him, in making beautiful cake cinnabar in 1782, and in
1785 vermilion also, in the newly-built works on the right bank of the
Idriza.
In 1796 Oberhüttenverwalter (manager of the works) Leopold v. Passetzky
introduced the sublimate and precipitate manufacture, but it was
abandoned as unprofitable in 1824.
The many foreign attempts to manufacture vermilion in the wet way
caused similar ones here, as those of Fabriks-Controlor Rabitsch in
1838, and later of Hüttenverwalter M. Glowacki, which brought large
amounts of the vermilion so manufactured into the market. Still this
manufacture came to no full development, and became forgotten, until,
finally, in the years 1877 and 1878, experiments led to its being
discontinued on account of the costliness and uncertainty of the
method. A new set of experiments in 1878 and 1879, by Assayer E. Teuber
and Director of Works (Hüttenverwalter) H. Langer, under the direction
of the Imperial Agricultural Ministry, led to favourable results. A
new manufactory, set in operation in 1880, furnishes three sorts of
vermilion manufactured in the wet way.
The arrangements of the works for the manufacture of vermilion in
the dry way consist of:--One sulphur stamp battery. One amalgamating
plant with eighteen small barrels; both pieces of apparatus being
driven by a two horse-power water-wheel. Four sublimation furnaces,
each with six retorts of cast iron. Four vermilion mills, each driven
by a water-wheel of 2·5 horse-power. Kettles and vats for heating,
digesting, and refining the ground cinnabar. One drying hearth. The
preparation of vermilion as an article of commerce, falls into several
separate operations, viz.:
1. Amalgamation; i. e. preparation of the raw mohr.
2. Sublimation; i. e. preparation of the cake cinnabar.
3. Grinding of the cake cinnabar, refining and drying of the vermilion.
For the preparation of the raw mohr, for each charge of eighteen kegs
there are taken 80·64 kg. (117½ lb.) powdered and sifted sulphur, and
423·36 kg. (731½ lb.) of quicksilver.
The amalgamating kegs each contain 28 kg. (61½ lb.) of the charge, and
are given intermittent rotating motion by a rack and pinion driven by
a water-wheel. After an average of two and three-quarter hours, the
amalgamation is complete, and the raw mohr is taken from the casks.
For the sublimation, four furnaces are used, each with six pear-shaped
cast-iron retorts of considerable thickness. Each is charged with
58 kg. (127½ lb.) of mohr, the mouth covered with a loosely placed
sheet-iron helmet, the furnace being slowly fired; the combination
of the sulphur and the quicksilver then results in about fifteen
minutes, with a detonation. As soon as this operation (das Abdampfen)
is over, a clay helmet is placed over the retort, and the firing is
increased, so that after two hours and twenty minutes the excess
of sulphur evaporates from the tube. The condenser is now added
(Stückperiode--Cake-period) and luted, then the firing is still more
urged, whereupon the cinnabar volatilises and deposits itself upon the
glazed earthenware condensation apparatus (tube, helmet, &c.). After
four hours, the sublimation is complete, and there is furnished by
the helmet 69 per cent., by the tubes 26 per cent., by the condenser
(Vorlage) 2 per cent., cinnabar.
The grinding of the cake cinnabar takes place in four mills driven by
an undershot water-wheel. These mills have a fixed under and upper
movable stone, and the grinding is done with water. The vermilion which
leaves the spout and runs into glazed clay vessels has a temperature of
about 100° F., that of the air being 59° F. The millstones make forty
revolutions per minute, and after each passage of the charge are placed
nearer together.
(2) A German chemist named Fleck has discovered that when a warm
solution of hyposulphite of soda is added to a double salt of mercury,
such as chloride of mercury and sodium, the solution becomes acid,
and black sulphide of mercury is deposited. But if the hyposulphite
solution is added in excess, and the temperature is not allowed to
rise beyond 140° F., the solution remains neutral, and red sulphide of
mercury, or vermilion, is deposited. The least quantity of acid causes
the production of the black sulphide. The presence of a salt of zinc
facilitates the production of the vermilion. The best method is as
follows:--To four equivalents of hyposulphite of soda mixed with four
equivalents of sulphate of zinc in diluted solution, is added, drop by
drop, a solution containing one equivalent of corrosive sublimate. The
whole is gently heated for 60 hours, at a temperature of 112° to 130° F.
(3) The following account of vermilion manufacture in China appeared
over the initials T. I. B., in the _Chemical News_.
The Chinaman has no knowledge whatever of chemistry, and of the
principles of natural philosophy and statics generally his notions
are of the most rudimentary and primitive description. How, then, in
the face of these obvious disadvantages have the Chinese contrived to
place themselves in the front rank amongst nations in the matter of
certain chemical manufactures, one of the most important of which is
the subject of this article--Vermilion?
We have seen with what ingenuity and pertinacity in carrying out his
ends the Chinaman has succeeded in making perhaps the most delicate and
perfect iron castings in the world. He has succeeded in that instance,
not by any deep researches into the hidden mysteries of Nature, by
no process of thought involving an enquiry into the “reason why”; to
this the Chinaman is averse, the whole tendency of his education,
such as it is, tends to make him satisfied with observing effects; it
is sufficient to him to know that things are so, without going into
troublesome or elaborate investigations into those changeless laws of
Nature into which his philosophy teaches him that, as he cannot alter
or control, research is fruitless: but that he has in his own small,
ingenious, patient way observed effects to very good purpose, the
unrivalled excellence of some of his manufactures testifies.
We will now enter a vermilion manufactory and watch the process from
the first stage of mixing its two ingredients--mercury and sulphur--to
the final process of weighing and packing this costly and beautiful
pigment for the market.
The first objects to attract the visitor’s attention on entering the
yard attached to the works will probably be large piles or stacks of
charcoal, crates or baskets of broken crockery ware, and numerous rusty
old iron pans of somewhat similar shape to rice pans, but considerably
thicker and heavier. There will also probably be a few broken and
disused cast-iron mortars. All these articles are the cast off or worn
out implements of the manufacture, and will be described in their
proper order.
On entering the factory proper, scores of little stone mills, each
being turned by one man, and other long rows of workmen weighing out
and wrapping up the vermilion, will be seen. The furnaces are then
arrived at: there may be a score or more in number, and may be ten or
twelve in each furnace room, five or six on each side. After passing
these, the stores of quicksilver, sulphur, alum, glue, new spare iron
pans, serviceable crockery ware, and sieves and other utensils used in
the factory are arrived at, and this completes the view of the works.
The iron pans in which the vermilion is sublimed are those referred to
above; they are circular and hemispherical in shape; all are of the
same size and weight; they are cast upside down, and in the casting,
a runner or lump of iron, two and three-eighths inches in diameter
by from six-eighths to one inch in depth, is purposely left on every
pan in order to enable the workman the more readily to handle the pan
when stirring up its contents. The size of the pans proved by actual
measurement to be 29¼ inches in diameter, by 8⅞ inches deep, and the
weight 40 catties, or say about 53 lb.
These pans are set in rows of 5 or 6 on each side of a small
rectangular room, in size some 12 feet by 15 feet; the door of this
room is of wood and contains an aperture a few inches square in order
to enable the workman to watch the progress of his operation, from
time to time, without the necessity of lowering the temperature of the
apartment by opening the door. The pans are set in brickwork, each
pan having beneath it a grate to hold the charcoal used as fuel. There
is no communication between the grates or furnaces under each pan, and
no chimney, the flames and products of combustion finding exit from
the front of the grate, which is left wholly open at all stages of the
operation.
The process of manufacture is as follows:--Taking an iron pan which
is of 4 inches smaller diameter than those described, and also in
all other respects proportionally less, except the runner, which is
of the same size, a skilled workman proceeds to weigh out 17⅓ lb. of
sulphur. This he places in the pan, and adds about half the contents
of a bottle of quicksilver. The pan with its contents is then put upon
a small earthen brazier or portable furnace, the fuel used in which is
charcoal. When the sulphur is sufficiently melted, the workman, taking
an iron spatula or stirrer, rapidly stirs up the quicksilver with the
sulphur, and gradually adds the remaining contents of the bottle of
quicksilver, stirring the two ingredients together meanwhile until the
mercury has wholly disappeared, or “been killed,” as the Chinese put it.
When this takes place, the pan is removed from the fire, a small
quantity of water is added, and rapidly stirred up with the contents
of the pan, which have now assumed a dark blood-red appearance and
semi-crystalline structure. This mass is then turned out of the pan
into an iron mortar, and then broken up into a coarse powder. This
forms a charge for one of the large pans previously described, and when
sufficient material has been prepared to charge all the pans in one
furnace chamber the sublimation is proceeded with as follows:--
All the pans having received their quantum of crude vermilion, this is
covered with a number of crockery-or porcelain-ware plates, of tough,
strong manufacture, each about 8 inches in diameter; some of these
plates, however, are broken up, and are in a more or less fragmentary
condition. When these plates have been piled up into a dome-shaped
heap of the same shape as the bottom of the upper pan, to which they
should extend, the whole is covered with one of the smaller pans
previously described.
Now it will be remembered that the smaller pan was of 4 inches less
diameter than the larger one; there will consequently be a circular
space two inches all round between the circumferences of the pans.
Consequently the rim of the upper or covering pan will be about 2
inches lower than the rim of the lower pan; there will also be some 4
inches space horizontally between the rim of the large lower pan and
that portion of the smaller pan which is at the same height as the rim
of the larger one. This space is carefully filled with a clay luting
into which some holes, generally about four in number, are pierced,
extending down to the rim of the smaller pan or cover; this is done in
order to allow the heated air and other matters to escape.
All the pans in one furnace chamber being thus charged and covered, the
fires are lighted. The flames from the charcoal should occasionally
play several feet above the mouths of the furnaces. The door of the
chamber is kept closed, except when it is open for a moment in order
to enable the workmen to replenish the fires, which must be kept
up at a fierce heat for eighteen hours. During this process a blue
lambent flame is seen to play above each of the four holes which are
pierced through the clay luting of the pans, so it is evident that a
considerable quantity of either one or probably both the ingredients is
wasted. After eighteen hours the fires are allowed to go out, and the
contents of the pan cool down.
When this is accomplished, the greater portion of the vermilion will
be found adhering to the lower surface of the broken-up porcelain
plates with which the crude product is covered. The vermilion is then
carefully removed from the porcelain by means of chisels, and is now
ready for the elutriating mills. Another portion of vermilion of not
so good quality is found adhering to the upper iron pan, and that
obtained by washing the clay luting in a cradle, as diggers wash dirt
for gold. This, together with the wipings and scrapings generally,
is mixed up with alum and glue-water into cakes, and, after drying
on a brick surface heated beneath by means of wood or charcoal, is
powdered up on a mortar, and re-sublimed when a sufficient quantity has
accumulated.
The vermilion which was removed from the porcelain plates is of a
blood-red colour and crystalline structure. This is then powdered up in
a mortar and removed to the levigating mills. These are the ordinary
little horizontal stone mills used by Chinese and other natives of the
East to grind rice and other grain into flour or pulp, as the case
may be. Each stone is about 2½ feet in diameter; the lower stone is
stationary, the upper is turned by a direct-acting piece of wood having
a hole in it which works a wooden peg affixed to the upper stone,
which is made to revolve by a backward and forward movement of the
piece of wood, or handle, some 3 or 4 feet long, previously mentioned.
One man turns each mill. The upper stone has a small hole in it near
its centre, down which the workman from time to time pours a little
spoonful of the powdered vermilion, which he washes down into the mill
with water; as he turns the mill, the workman keeps continually ladling
little spoonfuls of water down the aperture or hole in the upper stone;
the ground and thus elutriated vermilion, as it escapes from between
the stones, is washed down by the water into a vessel placed beneath to
receive it.
When work is suspended for the evening, the ground vermilion is
carefully stirred up with a solution of glue and alum in water, in
the proportion of about an ounce of each to the gallon. The glue has
been made to mix with the water by previously heating it with a small
quantity of water; the earthen pots in which this process is effected
each hold about 6 gallons. The mixture is then left to settle. In
the following morning the mixture of glue and alum is poured off the
vermilion, and the upper portion of the cake of vermilion at the bottom
of the vessel--that is, the portion which remained longest suspended in
the liquid--will be found to be in a much finer state of subdivision
than the lower portion, which requires to be again elutriated as on the
previous day: this separation of the more finely divided vermilion from
that which was coarser, by suspension in a dense medium, is a really
most ingenious process, for which we should give the Chinaman every
credit.
The process of grinding, elutriation, and separation of the coarsely
ground from the fine vermilion, sometimes requires to be several times
repeated, in order to fully bring out the colour. As a final process
the damp cake of finely ground vermilion is stirred up with clean
water, and allowed to settle down until the next morning, when the
water is carefully poured off into large wooden vats to still further
deposit a small quantity of vermilion yet remaining in suspension, and
the vermilion is dried in the open air on the roof of the premises.
When quite dried, the cakes of now full-coloured pigment are carefully
powdered, and sifted by means of square muslin-bottomed sieves,
contained in a covered box some 2 feet high by 2½ wide, in which the
sieves, which slide on a framework inside the box, are jerked backwards
and forwards by means of a handle on the outside of the box or case
containing them.
The now fully-prepared vermilion is removed to the packing house, where
may be seen rows of workmen, men and boys, seated before a series of
tables. Between every two workmen is a third, with a small pair of
scales, which he holds in his left hand; and as the workmen on either
side place before him the little pieces of paper in which the vermilion
is to be wrapped up, he weighs into each paper one tael (about an ounce
and a third avoirdupois) weight of vermilion; the papers are two in
number, the inner a black or prepared paper, and the outer a piece of
ordinary white paper. After being wrapped up, the packets are placed
in rows before another workman, who stamps them with a seal containing
in Chinese characters the name and address of the manufactory in which
the article has been made, and the quantity and quality of vermilion
contained in the packet.
The rapidity and deftness of the Chinese workmen at this employment
is really surprising; the stamping, for instance, is effected at the
average rate of sixty impressions per minute, and the wrapping up is
carried on with proportionate rapidity. The mixture of alum, which is
the ordinary aluminium potassium sulphate, with the vermilion, in one
of its stages of manufacture as described above, is not added, as at
first sight we thought it might be, merely to assist in clarifying or
purifying the water by causing it to deposit its sediment, but seems
to have some peculiar effect upon the colour, although what may be the
_rationale_ of the process, or how it acts, we cannot quite clearly
see. The glue is added as described above merely to favour separation
of the finely elutriated vermilion by holding it longer in suspension
than the coarser particles, which sink first, and may therefore be
separated in their order of stratification.
The actual composition of vermilion is 100 parts of mercury to 16 of
sulphur, when both these ingredients are in a perfectly pure state;
the excess of 5⅓ lb. of sulphur added by the Chinese is probably
volatilised and lost in the process of sublimation, or, as the sulphur
used is generally not quite pure, a part may go for foreign matter
contained in the sulphur; the balance being probably the _raison
d’être_ of the blue lambent flame seen playing over the apertures
in the luting during the sublimation process. For a people having,
like the Chinese, no acquaintance with even the first rudiments of
chemistry, the proportion of ingredients taken--56¼ catties to 13
catties, or say 75 lb. to 17⅓ lb.--shows wonderfully accurate powers
of observation and a knowledge of combining proportions only to be
gained by much experience and a long extended series of careful
observations highly creditable to the manufacturers. The entire process
is one of the most ingenious and interesting to be seen in any part of
the world.--(T. I. B.)
Another and briefer account of the Chinese vermilion manufacture is
given by H. Maccallum, in the Proceedings of the Pharmaceutical Society.
He says there are three vermilion works in Hong Kong, the method of
manufacture being exactly the same in each. The largest works consume
about 6000 bottles of mercury annually, and it was in this one that the
following operations were witnessed:--
First Step.--A large, very thin iron pan, containing a weighed
quantity, about 14 lb., of sulphur, is placed over a slow fire, and
two-thirds of a bottle of mercury added; as soon as the sulphur begins
to melt, the mixture is vigorously stirred with an iron stirrer until
it assumes a black pulverulent appearance with some melted sulphur
floating on the surface; it is then removed from the fire and the
remainder of the bottle of mercury is added, the whole being well
stirred. A little water is now poured over the mass, which rapidly
cools it; the pan is immediately emptied, when it is again ready
for the next batch. The whole operation does not last more than ten
minutes. The resulting black powder is not a definite sulphide, as
uncombined mercury can be seen throughout the whole mass; besides, the
quantity of sulphur used is much in excess of the amount required to
form mercuric sulphide.
Second Step.--The black powder obtained in the first step is placed
in a semi-hemispherical iron pan, built in with brick, and having
a fireplace beneath, covered over with broken pieces of porcelain.
These are built up in a loose porous manner, so as to fill another
semi-hemispherical iron pan, which is then placed over the fixed one
and securely luted with clay, a large stone being placed on the top
of it to assist in keeping it in its place. The fire is then lighted
and kept up for sixteen hours. The whole is then allowed to cool. When
the top pan is removed, the vermilion, together with the greater part
of the broken porcelain, is attached to it in a coherent mass, which
is easily separated into its component parts. The surfaces of the
vermilion which were attached to the porcelain have a brownish red and
polished appearance, the broken surfaces being somewhat brighter and
crystalline.
Third Step.--The sublimed mass obtained in the second step is pounded
in a mortar to a coarse powder, and then ground with water between
two stones, somewhat after the manner of grinding corn. The resulting
semi-fluid mass is transferred to large vats of water and allowed to
settle, the supernatant water is removed, and the sediment is dried
at a gentle heat; when dried, it is again powdered, passed through a
sieve, and is then fit for the market.--_Proc. Pharm. Soc._
(4) Firmenich describes a process which he declares gives better
results in the beauty of colour than any other. It consists in using
sulphide of potassium, which must be in a state of great purity. Of the
various methods for preparing potassium sulphide, Firmenich rejects
those in which caustic potash lye is boiled with excess of flowers of
sulphur, on account of the simultaneous formation of a hyposulphite
or sulphate of potash, which interferes in the preparation of the
vermilion.
The process adopted by Firmenich for making pure potassium sulphide is
to reduce sulphate of potash by heating with charcoal, and subsequently
saturating the lye with sulphur to the necessary degree.
Usually about 20 parts by weight of potassium sulphate and 6 parts
by weight of charcoal are reduced to very fine powder and thoroughly
incorporated. Placed in a Hessian crucible, the mass is covered,
luted, and strongly heated. As considerable ebullition takes place
the crucible should be of such a size that the charge only occupies
two-thirds of its capacity. After fusion is complete, the mass,
which is now potassium sulphide, is allowed to cool; it presents a
reddish-brown crystalline appearance, and is very hygroscopic. It is
put into a cast-iron pan, with addition of soft water in the proportion
of 7 parts of water to every 2 parts of the potassium sulphide; after
boiling, it is filtered and on cooling, the undecomposed sulphate of
potash collects in crystals attached to the sides of the pan.
The thus purified lye is boiled a second time with flowers of sulphur,
added in small doses until saturation is indicated by bubbling and
effervescence. The simple (monosulphide) potassium sulphide in this
manner takes up four additional atoms of sulphur, and becomes the
pentasulphide.
The preparation of the vermilion then proceeds in the following
manner:--Into a series of large flasks are put 11 lb. of mercury, 5
lb. of the potassium sulphide lye, and 2¼ lb. of sulphur. The contents
are subjected to a moderate heat, and the flasks are then agitated in
a curious manner by arranging them in pairs in baskets suspended from
strings, over a straw mattress, on which the baskets bump each time
they descend.
Occasionally the flasks are turned about, and after about two hours of
this agitation they commence to grow hot, and the contents assume a
greenish-brown colour. The lye is robbed of its sulphur by the mercury,
and replenishes itself from the excess added.
Complete combination of the mercury and sulphur is accomplished in
about three and a half hours, when the colour of the mass becomes dark
brown. The next step is to cool the compound, an operation which must
proceed very slowly, and should occupy about five hours.
Development of the colour is effected by heat, for which purpose the
flasks are placed in a stove room or water bath, and subjected to a
temperature which does not fluctuate beyond 113° and 122° F., under
the influence of which the red colour appears. The greatest care is
necessary in this heating process, as it determines the success or
failure of the colour. It lasts several days, during which the flasks
should be shaken three or four times daily.
In order to separate the vermilion from the excess of sulphur, water is
added to the contents of each bottle, and, after thorough shaking, the
whole is turned out into a filter. The clear liquor escapes, and the
residual vermilion is mixed with caustic soda lye in stoneware jars,
and thus the remaining free sulphur is dissolved out. Subsequently
the lye is poured off as completely as possible, and the deposit is
repeatedly washed, first by decantation and finally on a filter. The
whole operation of filtering and washing cannot be completed in less
than two or three days. When this is finished, the drying must be
carried on at a very low temperature, till the vermilion can readily
be broken and is dry to the touch, when it is put into iron basins and
repeatedly stirred, while the temperature is allowed to reach 143° F.,
but never beyond that. The final desiccation occupies about five hours.
Vermilion made in this way is reputed more permanent and less costly
than by the usual methods.
(5) Dutch vermilion has a good name, and one method adopted in Holland
is as follows:--A mixture of 2 lb. of mercury and 1 lb. of sulphur
is thoroughly ground, and to 100 lb. of the mixture are added 2½ lb.
of minium or of granulated lead. About 2 cwt. of the compound is put
into each sublimation pot, which is duly heated. When the operation is
finished, the pots are allowed to cool for eighteen to twenty hours,
when they are broken, and their contents are ground in a mill. The lead
remains as a sulphide in the bottom of the pots.
(6) A modification of the Dutch method consists in making an intimate
mixture of 54 lb. of mercury squeezed through chamois leather and
7½ lb. of flowers of sulphur, which is then moderately heated on a
shallow iron dish, and the resulting black sulphide (“ethiops”) is
coarsely broken, ground, and kept in pots. To convert the ethiops into
vermilion, the former is put into large clay crucibles in a furnace,
and heated to dark-redness, whereupon the mass takes fire. As soon as
the flame has subsided, the crucibles are covered with a close-fitting
iron plate, and the firing is continued for thirty-six hours. The mass
is stirred every half-hour with an iron rod, and fresh additions of
ethiops are made at four or five hours’ intervals. The vermilion is
sublimed, and condenses on the cool portion of the interior of the
crucibles, whence it is collected by breaking the crucibles when cold,
and is finally ground and levigated.
(7) Kirchoff’s method requires special care, and consists in grinding
300 lb. of mercury with 68 lb. of flowers of sulphur in a mortar, the
sulphur being first moistened with a few drops of caustic potash. The
resulting black sulphide of mercury is added to 160 lb. of caustic
potash dissolved in very little water, and the whole is heated for half
an hour on a sand bath, with occasional addition of water to make up
for loss by evaporation. Gradually the mass, under constant agitation,
becomes brown and gelatinous, and finally red. Thereupon it is carried
to the stove room and still agitated at intervals. After several
washings it is drained, and dried very gently.
(8) Weshle mixes finely powdered cinnabar with 1 per cent. of antimony
sulphide, and boils the mixture several times with three parts of
potassium sulphide in a cast-iron pot. The precipitate is water-washed,
digested with hydrochloric acid, washed again, and finally dried.
(9) Jacquelin takes 90 lb. of mercury, 30 of sulphur, 30 of water, and
20 of hydrated potash; the mercury and sulphur are put into a shallow
cast-iron dish, dipping into cold water, and the potash solution
is added by degrees while the mass is kept in agitation. Then the
mixture is heated for an hour at 176° F., the evaporated water being
replenished. The vermilion is washed in an excess of boiling water, and
again several times in cold water, and finally filtered and dried.
VICTORIA RED.--One of the fancy names for Derby red. (See p.
145.)