prussiate.
Deep. (3) 1 cwt. gypsum, 7½ lb. green copperas, 7½ lb. yellow
prussiate.
In each case about 50-60 gallons of water are required.
To determine the amount of barytes present in a sample, boil about 50
gr. with caustic soda, filter, wash the residue free from soda, treat
with sulphuric acid, well wash the insoluble residue, dry, and weigh.
CHINESE BLUE.--This well-known and favourite form of Prussian
blue is prepared with great care, and is usually sold in fine powder
or little cubes. Its composition is virtually identical with that
of ordinary Prussian blue, but it is more free from impurities, and
shows a fine bronze bloom or lustre on newly fractured surfaces. Being
pure, it is entirely dissolved by oxalic acid; and its composition
is about 52 per cent. oxide of iron, 43½ cyanogen, and 4½ water. In
dyeing and calico-printing it is extensively employed. Its tint varies
from greenish to violet, according to modifications in the method of
manufacture, the chief difference being that yellow prussiate gives a
greenish tone and red prussiate a violet.
The process of preparation is mainly as follows. In about 40 gallons
of cold water dissolve 1 cwt. of green copperas selecting it carefully
for freedom from insoluble oxide; add about 5 pints of sulphuric acid.
This liquor very rapidly undergoes oxidation, by which oxide of iron
is thrown down, and the solution is rendered unfit for making the best
quality pigment. Therefore it should be prepared only immediately
before it is used. In another vessel containing about 40 gallons of
cold water, dissolve 1 cwt. of yellow prussiate (if a green shade is
desired), or of red prussiate (if a violet tint is wished for). Even
larger quantities of water may be used for the solutions, as the more
dilute they are the finer is the colour precipitated and the greater
the lustre on the surface of the finished pigment.
When the two solutions of yellow or red prussiate and acidified green
copperas are brought together, a bluish-white precipitate is thrown
down. This is allowed to completely separate itself, and then the clear
supernatant liquid is drawn off.
The next step is to thoroughly oxidise the precipitate. This cannot be
satisfactorily accomplished by utilising the oxygen of the atmosphere,
as is done in other cases, because that method entails the production
of a certain amount of oxide of iron, which prejudicially affects the
purity of colour of the finished article. Of the chemical oxidising
agents which are available, the most satisfactory in point of cost
and efficiency is chloride of lime (bleaching powder). For each cwt.
of green copperas, mix about 20 lb. of bleaching powder into a thin
cream with water, and add it, in small quantities at a time, to the
precipitate, constantly stirring so as to ensure the absorption of
the whole of the chlorine by the blue. Without the addition be made
gradually and under agitation, the chlorine will be generated more
quickly than it can be absorbed, entailing a waste of gas and a noxious
vapour to be breathed by the workmen. Sometimes the bleaching powder is
added at an earlier stage, viz. to the green copperas solution, and in
that case the blue assumes a violet tone.
After the addition of the bleaching powder solution to the bluish-white
precipitate, it is acidified with hydrochloric acid, which develops
the blue. When the whole has settled, the supernatant liquor is drawn
off, and the blue powder is well washed and strained on a filter,
then placed in pans and dried very gradually indeed in the dark, at a
temperature never exceeding 130° F. The slower the drying the better
is the gloss of the pigment. It is most essential that iron be excluded
during the final grinding operation, or it may cause ignition of the
mass, and its conversion into oxide of iron would speedily follow.
It has been proposed to treat the white precipitate (obtained in the
usual manner from green copperas and yellow prussiate) by the chlorine
contained in aqua regia (nitro-hydrochloric acid). The copperas,
however, must be as free as possible from basic sulphate (oxide), which
is ensured by keeping a little metallic iron in the acid solution
of copperas. It is also desirable to effect the precipitation with
crude prussiate, so as to avoid absorption of oxygen and premature
development of the blue colour. Habich considers that the mistake is
generally made of using too little copperas, and he has found that when
90 lb. of copperas have been added to 100 lb. of yellow prussiate, a
drop of iron solution in the filtered liquor produces no precipitate,
while the white precipitate has carried with it a certain proportion of
prussiate, which can be washed out. He therefore proposes to avoid this
waste by pouring the copperas solution into the prussiate solution,
with constant agitation, till no further precipitate goes down, then
adding one volume of the copperas solution equal to one-ninth of that
already used. After fifteen minutes stirring, it is certain that all
the prussiate carried down is decomposed.
The drained precipitate is blued (peroxidised) by adding aqua regia
prepared several days previously, and in proportions depending on the
strengths of the two acids. Generally, the aqua regia mixture will be
100 lb. of commercial nitric acid at 30° B. (containing 35·4 lb. of
anhydrous acid) and 62·2 lb. commercial hydrochloric acid at 23° B.
(containing 23·9 lb. of the anhydrous acid); and 40 lb. of this mixture
will suffice for bluing the precipitate resulting from 100 lb. yellow
prussiate. The addition of the aqua regia should take place in a
wooden vessel with constant agitation.
According to another modification, the white precipitate obtained in
the usual way is blued by adding a solution of perchloride of iron,
which may be made from a hematite ore free from clay and carbonate of
lime, or from rouge. The iron oxide, from whatever source, is ground
to a very fine state, and treated with crude hydrochloric acid in
a lead-lined tank, where the mixture remains for several days, and
is constantly stirred. When saturated with iron the clear liquid is
withdrawn for use. To receive it, the white precipitate is rapidly
heated to boiling in a copper vessel, and is then transferred to a
wooden vat, and the iron perchloride solution is stirred in till the
desired tint is produced. The pigment is washed and dried in the
ordinary way, while the supernatant liquor (essentially protochloride
of iron) is poured over old scrap iron and used instead of copperas for
a fresh batch of yellow prussiate.
A solution of perchloride of manganese may be used instead of
perchloride of iron. Inferior qualities of manganese ore can be
employed, and the residues left after treatment with hydrochloric acid
may be washed and dried for sale as purified or peroxidised manganese.
PARIS BLUE.--(1) A synonym for the violet-tinted kind of
Prussian blue.
(2) A series of compounds described below. [_a_] A thorough mixture of
2 parts sulphur and 1 part dry carbonate of soda is gradually heated
in a covered crucible to redness or till fused; a mixture of silicate
of soda and aluminate of soda is then sprinkled in, and the heat is
continued for an hour; the little free sulphur present may be washed
out by water. [_b_] An intimate mixture of 37 parts china-clay, 15
parts sulphate of soda, 22 parts carbonate of soda, 18 parts sulphur,
and 8 parts charcoal, is heated in large crucibles for 24-30 hours;
the mass is re-heated in cast-iron boxes at a moderate temperature
till the desired tint appears, and is finally pulverised, washed, and
dried. [_c_] Gently fuse 1075 oz. crystallised carbonate of soda in its
water of crystallisation; shake in 5 oz. finely-pulverised orpiment,
and, when partly decomposed, as much gelatinous alumina hydrate as
contains 7 oz. anhydrous alumina; add 100 oz. finely-sifted clay, and
221 oz. flowers of sulphur; place the whole in a covered crucible,
and heat gently till the water is driven off, then to redness, so
that the ingredients sinter together without fusing; the mass is then
cooled, finely pulverised, suspended in river-water, and filtered. The
product is heated in a covered dish to dull redness for 1-2 hours, with
occasional stirring. Colourless or brownish patches may occur, and must
be removed.
SAXON BLUE.--Following is a recipe for the preparation of this
pigment, which possesses limited importance.
Dissolve 8 lb. alum and 1 lb. green copperas in 16 gallons of
water. Add separate solutions of pearlash and yellow prussiate till
precipitate ceases to go down. Collect the precipitate when it has
completely settled; wash thoroughly, and dry.
SOLUBLE BLUE.--This term is applied to a variety of Prussian
blue which, while possessing no difference in the matter of chemical
composition, yet has the distinctive feature of being soluble in water,
which the other varieties are not. It no longer enjoys the popularity
it once had as a dye, on account of the severe competition of the
coal-tar colours. Below are some of the most satisfactory formulæ for
its preparation.
(1) Mix 10 lb. of Prussian blue thoroughly in about 10 gallons of cold
water. Then add 5 lb. of yellow prussiate and let the whole mass boil
steadily for several hours. Strain off the liquor and well wash the
precipitate on a filter. Finally dry for use.
(2) Dissolve about 1 cwt. of red prussiate in water and make the
solution hot. Prepare another solution of about 73 lb. of green
copperas in hot water. Mix the two solutions together and boil them for
about a couple of hours. Allow the solid matters to settle out, then
put them on a filter and wash with clean water until a blue coloration
manifests itself in the drainings. The blue residue is then dried as
usual.
(3) Make one solution of 10 lb. of yellow prussiate, and another of 8
lb. of green copperas, water being the solvent in both cases. Mix these
two solutions together and give them an hour’s boiling.
Add 3 lb. of a mixture of nitro-sulphuric acid, containing 2 parts of
the former to 1 of the latter. Boil for another hour. Let the solid
pigment precipitate itself thoroughly, and then filter, wash, and dry
as in the other cases.
(4) Dissolve about 1 cwt. of perchloride of iron and 10 lb. of sulphate
of soda in water. Also dissolve in another vessel 2 cwt. of yellow
prussiate and 10 lb. of sulphate of soda. Pour the first solution
into the second (never the contrary) and take care that the prussiate
solution is always preponderant. The Glauber’s salt is useful in
rendering the precipitation of the blue pigment more complete by
reason of the insolubility of the latter in saline fluids. When the
blue sediment is all thrown down it is drained off on a filter, and
repeatedly washed till a blue tint appears in the wash-waters, when it
is dried for use.
TURNBULL’S BLUE.--This is an old-fashioned name often applied,
like the term Paris blue, to the violet shades of Prussian blue which
have been prepared with red prussiate.
=Ultramarine.=--According to Rowland Williams, F.C.S., natural
ultramarine is, perhaps, the most beautiful blue pigment known. It
was formerly, and is now to a small extent, manufactured (chiefly
for artists’ use) from lapis lazuli, a blue mineral which occurs,
intermixed with limestone and iron pyrites, in Siberia, Thibet, and
China. In order to obtain ultramarine from lapis lazuli, the roughly
pulverised mineral is ignited, dipped into vinegar to remove carbonate
of lime, and then reduced to the finest possible state of division.
The powder is next mixed with a cement composed of rosin, linseed oil,
white wax, and Burgundy pitch, and the resultant paste is worked under
water until all the ultramarine is separated. The ultramarine is washed
several times with water, and afterwards with alcohol, which removes
any of the resinous compound which may have adhered. When treated in
this manner, lapis lazuli yields from 2 to 3 per cent. of ultramarine.
According to Clement and Desormes, lapis lazuli has the following
composition:--
Per cent.
Soda 23·2
Alumina 34·8
Silica 35·8
Sulphur 3·1
Carbonate of lime 3·1
-----
100·0
It will be seen, therefore, that ultramarine essentially consists of
alumina, silica, soda, and sulphur, and may be regarded as a sodium
aluminium sulphate, in combination either with polysulphide of sodium
alone, or with a polysulphide and a polythionate of sodium. Clement
and Desormes believe that the iron in lazulite (lapis lazuli) is an
accidental impurity, and is neither essential to the mineral itself nor
to the ultramarine derived from it. There is still some doubt on this
point, however, many eminent chemists holding the opinion that iron is
a necessary constituent of ultramarine blue.
Natural ultramarine has been almost entirely replaced by the artificial
product, since methods have been devised for the manufacture of the
latter on a large scale. The possibility of preparing artificial
ultramarine suggested itself in a curious manner. About seventy years
ago a French alkali maker noticed the occasional appearance of a blue
coloured substance in his soda furnace. On analysis, Vauquelin found
the substance to have the same chemical composition as lapis lazuli,
and this incident led him to believe that ultramarine might be built up
from its elements. Several years passed away before Guimet succeeded in
manufacturing artificial ultramarine on anything like a large scale,
but Gmelin is said to have prepared it in small quantity half a dozen
years previously. There are four varieties of artificial ultramarine:
(1) the pure deep blue, equal in colour to average native ultramarine;
(2) pale blue; (3) violet or pink ultramarine; (4) green ultramarine.
The latter is obtained in the first stage of the ultramarine
manufacture, being the result of incomplete ignition of the materials
employed. Ultramarine is generally manufactured by one of the following
processes:--(_a_) “Sulphate”; (_b_) “Soda”; (_c_) “Silica.”
(_a_) “_Sulphate_” _Ultramarine_.--This may be prepared from sulphate
of soda (Glauber’s salt), charcoal, and kaolin (china clay). The
materials should be as free as possible from iron, and it has
been found that clay having approximately the formula Al_{2}O_{2}
(SiO_{2})_{2} gives the best results. The clay and sulphate of soda
must be thoroughly calcined. They are then intimately mixed with
charcoal in the following proportions:--
Per cent.
Clay 48·3
Sulphate of soda 43·5
Charcoal 8·2
-----
100·0
Sometimes a portion of the sulphate of soda is omitted, and some
carbonate of soda and sulphur added instead. The composition of the
mixture then becomes:--
Per cent.
Clay 47·2
Sulphate of soda 19·3
Carbonate of soda 19·3
Charcoal 8·1
Sulphur 6·1
-----
100·0
Caustic soda is also sometimes used instead of carbonate. These
mixtures (whether sulphate alone or sulphate and carbonate) are made
with a view to have the soda present in sufficient amount to combine
with one-half the silica contained in the clay, and to leave sufficient
soda to form polysulphide of sodium with a portion of the sulphur.
There should then remain enough soda and sulphur to produce ordinary
sulphide of sodium (Na_{2}S). If either of the two mixtures be ignited
out of contact with air, a white compound is formed, which is sometimes
termed white ultramarine. On leaving this exposed to the atmosphere for
some time it becomes green, and on further ignition, with free access
of air, it is converted into ultramarine blue. In actual working the
carefully prepared mixture of the above mentioned materials is heated
for several hours to a high temperature in fire-clay crucibles, only a
limited supply of air being allowed to enter, and the temperature being
eventually raised to a white heat. The product of this operation, when
cool, has a grey or yellowish-green appearance. It is washed several
times with water, dried, reduced to a fine powder, and then represents
the green ultramarine of commerce. Stölzel found that green ultramarine
had the following composition:--
Per cent.
Alumina 30·11
Silica 37·46
Sodium 19·09
Sulphur 6·08
Iron ·49
Calcium ·45
Chlorine ·37
Oxygen 5·19
Sulphuric acid ·76
Magnesia, potash, and phosphoric acid traces.
-------
100·00
Green ultramarine is transformed into blue by heating with about 4
per cent. of sulphur at a low temperature, with free access of air.
Sulphur is afterwards added, if necessary, in small quantities at a
time, and the heating is continued until the desired shade of blue is
obtained. The mass is then powdered, the soluble matter (sulphide of
soda, &c.) is removed by washing with water, and the blue is dried and
assorted according to quality.
(_b_) “_Soda_” _Ultramarine_ is sometimes made with soda alone (either
carbonate or caustic), and at others with a mixture of soda and
sulphate of soda. Rowland Williams found the following proportions of
the respective ingredients to answer satisfactorily:--
Per cent.
China clay 36·8
Carbonate of soda 36·8
Sulphur 22·0
Coal 4·4
-----
100·0
The proportions for soda and sulphate of soda ultramarine have been
previously given under “sulphate ultramarine.” The ignition is carried
on in a manner similar to that already described. The resultant
green product, owing to its avidity for oxygen, is partially changed
into ultramarine blue by simple contact with the air. It is entirely
converted into the blue variety by roasting with an additional quantity
of sulphur. With care, ultramarine blue may be manufactured in one
operation, by increasing the proportions of soda and sulphur.
(_c_) “_Silica_” _Ultramarine_ is manufactured in the same way as soda
ultramarine, except that, in addition to the other materials, silica to
the extent of 5 or 10 per cent. of the weight of clay is employed. By
this process, ultramarine blue of a slightly reddish tint is obtained
in one operation. The method has, however, one decided drawback, viz.
that the materials employed are rather liable to fuse during ignition.
The faintly reddish hue of “silica” ultramarine becomes more intense
according to the proportion of silica present. “Silica” ultramarine
is said by some to be less readily attacked by acids and by strong
alum solutions than ultramarine prepared by the “sulphate” and “soda”
processes; but Rowland Williams’ experience does not confirm this
statement. He mentions that good artificial ultramarine withstands
the action of weak acids much better than is generally imagined. He
had occasion to test many samples which resisted the action of dilute
acids to a remarkable degree. Most strong acids, of course, decompose
both artificial and native ultramarine, with evolution of sulphuretted
hydrogen. Native ultramarine is, however, less susceptible to the
influence of acids (both strong and dilute) than the artificial
compound. This difference of behaviour is probably due to the fact that
the former contains considerably less sulphur than the latter, and it
is also possible that the constituents of natural ultramarine may be
combined in a somewhat different manner from those of the artificial
product.
Notwithstanding the large amount of research with reference to the
chemical composition of ultramarine, the origin of its blue colour
still remains in doubt. According to Wilkens (_Ann. Ch. Pharm._, xcix.
21), ultramarine consists of two portions, one of which is easily
attacked by hydrochloric acid, and is regarded by him as the essential
constituent, whilst the other portion is insoluble in hydrochloric
acid, and contains variable proportions of clay, sand, oxide of iron,
and sulphuric acid. From his analyses of the pure blue, Wilkens
deduces the formula (2Al_{2}O_{3} 3SiO_{2}) (Al_{2}O_{3} 4SiO_{2})
Na_{2}S_{2}O_{3} 3Na_{2}S:--
Per cent.
Silica 37·6
Alumina 27·4
Sulphur 14·2
Soda (Na_{2}O) 20·0
----
99·2
Wilkens regards the blue colouring principle of ultramarine as a
compound of hyposulphite and sulphide of sodium. He considers the
presence of iron is not necessary for the production of the blue;
whilst Dr. Elsner, in a paper published in 1841, states that about 1
per cent. of iron (which he presumes to be in the state of sulphide)
is essential. Rowland Williams asks whether it is not conceivable
that the blue colour of ultramarine may be due to the presence of a
small quantity of black sulphide of iron, most intimately combined
with a colourless or comparatively colourless compound (such as white
ultramarine), the whole mass (owing to the dilution of the black
sulphide) showing a blue reflection.
Ultramarine is insoluble without decomposition in any known menstruum.
According to P. Ebell (Ber. 16), ultramarine, when in the most finely
divided state, will remain suspended in pure water for months. The
liquid may be filtered unchanged through several layers of Swedish
filter paper, and appears perfectly clear when examined in a ¾ in.
layer, and on evaporation deposits the ultramarine as a lustrous
coating on the sides of the vessel. Rowland Williams repeated the above
experiment, and can confirm Ebell’s statement. This result shows the
necessity of due precautions being taken during the washing of the
ultramarine in the process of manufacture, otherwise a considerable
amount of the finely divided blue may be lost. Ultramarine is largely
used in calico printing for pigment styles, being fixed on the fibre
by means of albumen. It is also employed for blueing linen and cotton,
wax candles, lump sugar, &c. Ultramarine is not adulterated to a large
extent, the chief sophistication being barium sulphate (barytes), and
occasionally chalk and china clay.--(Rowland Williams, in _Industries_.)
Another writer in _Industries_ says that the manufacture of ultramarine
has perhaps hardly received the attention it deserves in England. The
importance of the industry has been recognised in Germany, however,
and though the palmy days of the trade, when the whole production was
in the hands of a few firms, and the price was a matter of private
friendly arrangement, are gone for ever, yet the business is in a
flourishing state, and should prove lucrative if properly managed.
It is a characteristically English failing to overlook branches of
business not dealing with large quantities of staple commodities, and
thus many of the smaller but remunerative industries have passed out of
our hands. When one observes that almost every sheet of ordinary blue
official paper is decolorised when accidentally brought into contact
with an acid, betraying the fact at once that its colouring matter is
ultramarine, one realises that a very considerable consumption for
this and similar purposes must take place. Like most trades based upon
chemical principles, the manufacture of ultramarine has recently made
rapid strides, and some of the latest developments are recorded in
a paper by J. Wunder, appearing in a recent number of the _Chemiker
Zeitung_, which is worthy of some attention.
With most people not directly interested in it, the term ultramarine
is taken to mean the _blue_ pigment known under that name, the words
being reckoned almost synonymous. Others, more erudite, recognise the
existence of a green variety, but that the production of such colours
as red and violet is possible is scarcely suspected. Of course the
blue is the most important, but even that does not correspond to one
specific substance, products of different shade being prepared by
modifying the process of manufacture. As usually made, ultramarine is
formed by heating together carbonate of soda, kaolin, sulphur, and
charcoal, with limited access of air, the resulting pigment being
green; this, on roasting with sulphur, becomes blue. If the operation
be conducted with complete exclusion of air, so-called ultramarine
white (in reality _grey_) is produced, which becomes green on further
heating. Ultramarine blue capable of resisting the action of alum
is sometimes required, and may be obtained by the use of a highly
silicious charge and much sulphur, the burning being conducted in
crucibles or in mass according to the purpose for which the pigment
is required. The former process is costly, while the latter gives a
product containing a good deal of free sulphur, which is objectionable
for such purposes as calico printing. Removal of the excess of sulphur
by heat or caustic soda is not feasible, as the colour suffers in
either case, but a certain amount of success has attended experiments
with sodium sulphide, the colour often brightening noticeably.
It is curious that chemically pure sodium carbonate, or such as is made
by the ammonia-soda process, is not well fitted for the manufacture of
ultramarine; Leblanc soda, containing a little caustic, is distinctly
preferable. Sprinkling the soda with a strong solution of sodium
sulphide before use is a good plan, and one easy to adopt. The more
silicious the mixture the more difficulties are encountered, but the
product is a deeper, richer colour, and withstands the action of alum
and weak acids better. Excess of oxygen must be guarded against; many
a manufacturer has had a batch turn out a hard cold blue, instead of
a soft rich colour, solely on account of a too-excellent draught,
an accident especially liable to happen in winter time. So much
dreaded is this catastrophe that some makers habitually limit the air
supply--smothering the neighbourhood with smoke, and wasting coal. The
need for exact control here indicated points to a probable advantage
from the use of gaseous fuel. Considerable economy has resulted from
the use of the waste gases from one furnace serving for the preliminary
heating of another; a better plan would probably be the introduction of
regenerative heating.
The crude ultramarine as it comes from the furnace contains a large
proportion of soluble salts, notably 20 to 24 per cent. of sodium
sulphate, which have to be removed before it is merchantable. Usually,
after grinding, it is simply stirred up repeatedly with hot water and
the aqueous extract is siphoned off. That such a crude method should be
in vogue at the present time is very significant of the ample margin
of profit that must exist. By systematic extraction and filtration
under pressure the washing may be effected with so little water that
the solution is sufficiently concentrated to pay for evaporation by the
heat of waste furnace gases, the recovered sodium sulphate serving to
replace part of the raw material.
The quality of ultramarine largely depending upon its fineness, it
is graded by levigation, the coarser portions being filter pressed,
and the finest “floating” quality, which remains in suspension for an
inconveniently long time, precipitated by the addition of a trace of an
ammonium salt, gypsum, or even hard water, and filtered by the aid of a
suction tube on the principle of an ordinary Bunsen pump.
The first successful attempt to produce ultramarine _violet_ was made
by Professor Leykauf in 1859. By heating ordinary ultramarine with
calcium chloride in the presence of air and moisture, he obtained
a violet-toned pigment, but it was not a full colour. The active
substance in this change was probably hydrochloric acid, produced by
the decomposition of the calcium chloride. Later experiments with
other reagents, such as chlorine and gaseous hydrochloric acid, led to
the following methods being devised. In the first, ultramarine blue
is spread out on stoneware shelves in iron chambers and treated with
a mixture of chlorine and steam at a temperature of 300° F. to 480°
F. for about three hours. In the second, the plant is very similar,
but at the bottom of the chambers are stoneware dishes, into which
hydrochloric acid is poured from time to time. As the temperature is
raised, copious vapours arise from these, evaporation being aided
by a strong draught, and the ultramarine blue, after being kept at
428°-446° F. for some seven hours, becomes converted into a dull
violet, which brightens on continuing the process with a temperature
gradually falling to 320° F. The ultramarine violet produced by either
of the above methods resists the action of lime, and is of general
applicability.
The pigment produced by a third and simpler process, consisting merely
in heating ultramarine blue mixed with salammoniac and a little
sodium nitrate, is unfortunately not so stable. Another shade of
considerable interest is a pure bright light blue, formed by heating
the violet variety in hydrogen to about 536°-554° F. It has not yet
been prepared on a commercial scale, but certainly merits the attention
of manufacturers. An ultramarine red has been made by acting on the
violet produced by either of the first two methods with the vapour of
either nitric or hydrochloric acid at 275°-293° F., the sole essential
determining condition being the temperature. Iron vessels could be used
in the case of nitric acid at this temperature, but if hydrochloric
acid were employed stoneware would have to be substituted. In the
manufacture of the violet the temperature is above the limit at which
hydrochloric acid acts on iron.
It is now only necessary for some successful experimenter to put on the
market yellow and orange shades of ultramarine for almost the whole
of the spectrum to be represented. The problem of the cause of the
colour of ultramarine, attempts to solve which have been repeatedly
made, seems increasingly difficult when its protean character is
considered; but this from the industrial point of view is of secondary
importance, provided all required shades can be produced with ease and
economy. Nevertheless, it is certain that here, as in other cases,
substantial technical progress would follow from adequate scientific
investigation.--(_Industries._)
Ultramarine was also made the subject of a very interesting paper, by
Herbert J. L. Rawlins, read before the Society of Chemical Industry, in
December 1887.
After referring to the native form, lapis lazuli, Rawlins goes on
to observe that “analysis could give no clue as to the cause of
the blue colour. To prepare it artificially became a great object,
and the efforts in this direction were stimulated by the offer of
prizes, amongst which was one of 6000 francs, offered by the ‘Société
d’Encouragement’ of France, to be awarded to the discoverer of a method
of making ultramarine, provided it did not cost more than 90_s._ per
lb. How strange it seems to think of this in these days when the value
has fallen to less than half that price per cwt.!
“As early as 1814, two German chemists, Tessärt and Kuhlmann, had
observed the formation of a blue product in soda kilns and calcination
kilns, but Guimet, in 1828, first discovered how it was produced, and
gained the 6000 francs prize. He did not, however, publish his method,
and grew immensely rich, although the price sank to about 16_s._ per
lb. In 1828 he was producing at the rate of 120,000 lb. annually.
“About the same time, or, as is positively asserted by some, even prior
to Guimet, Gmelin made the same discovery and published his researches
in full, thus perhaps laying the foundation stone of the present
supremacy of Germany in this manufacture.
“In spite of the valuable discoveries of Hoffmann, Unger, and others,
our knowledge of the chemical constitution of ultramarine is very
limited and uncertain, many different theories having been advanced
regarding the cause of the blue colour.
“According to Wilkins, ultramarine is composed of two portions, one
of which consists of two silicates of alumina with sulphite and
sulphide of sodium, and is constant in its composition; the other
being a mixture of variable quantities of sand, clay and oxide of
iron, with sulphuric acid. The blue colouring principle he considers
to be a compound of sodium sulphite and sulphide. Another ingenious
theorist, Stein, in two papers published in the _Jahresberichte_ in
1871 and 1872, concludes that blue ultramarine contains sulphurous,
and not thiosulphuric acid, that neither sulphites nor thiosulphates
are necessary to its composition, and that it owes its colour to
the presence of black sulphide of sodium, which is formed at high
temperatures by the action of sulphide of sodium on alumina--admitting,
therefore, that it is not a chemical compound, but merely a mechanical
mixture, the blue colour of which is due to the bodies composing it.
“Brunner considers ultramarine to be a compound of aluminium silicate,
with sodium sulphate and sulphide; while Brünlin regards it as a double
silicate of aluminium and sodium, in combination with pentasulphide of
sodium. Green ultramarine he considers to be the same double silicate
in combination with bisulphide of sodium.
“Again, according to Ritter, ultramarine contains a double silicate,
not only associated with polysulphide, but also with thiosulphate of
soda; and Schülzenberger, on the other hand, considers that it is a
mixture of a double silicate with sulphite and monosulphide of sodium.
“Endemann considers that the blue colour is due to a ‘colour nucleus,’
consisting of unchanging proportions of aluminium, sodium, oxygen and
sulphur, in each variety of ultramarine the proportion being different,
while the rest of the sodium and aluminium and the whole of the silica
merely act as a vehicle necessary to the preparation and existence
of the colour. He considers that this ‘colour nucleus,’ in the case
of white ultramarine, which he calls the ‘mother-substance in the
manufacture of blue ultramarine,’ has the formula AlNa_{4}O_{2}S_{2}.
By the action on two molecules of this of sulphurous acid gas,
Na_{2}O is removed, and green ultramarine Al_{2}Na_{6}O_{3}S_{4}
is formed, which then, by the action of oxygen, which forms sodium
sulphate, passes into the pure green compound, having the formula
Al_{2}Na_{4}O_{3}S_{3}. In the ‘indirect process’ of manufacture, green
ultramarine is converted into blue by being burned with sulphur. By
this means Endemann considers that more sodium and sulphur are removed,
and blue ultramarine Al_{2}Na_{2}O_{3}S_{3} is formed. He considers
that the other portion, not included in the ‘colour nucleus,’ differs
in different samples. In one which he mentions it has about the
composition 3Al_{2}O_{3}.5Na_{2}O.16SiO_{2}.
“But of all chemists who have worked on this subject, none has done
more to increase our knowledge of ‘the blue marvel of inorganic
chemistry,’ as he himself has called it, than Reinhold Hoffmann.
His position of manager of the Marienberg Ultramarine Works, near
Benscheim, in the Grand Duchy of Hesse, renders his acquaintance with
the manufacture perfect, and his untiring researches on the subject
have been well rewarded by results both interesting and valuable.
He considers ultramarine to be a double silicate of sodium and
aluminium, together with bisulphide of sodium, the variety poor in
silica, characterised by its paleness and purity of tint, and easy
decomposition by acids, having the formula 4(Al_{2}Na_{2}Si_{2}O_{8})
+ Na_{2}S_{4}; while that rich in silica, characterised by its dark
and somewhat reddish tint, and more difficult decomposition by acids,
has the formula 2(Al_{2}Na_{2}Si_{3}O_{10}) + Na_{2}S_{4}. He also
considers it very doubtful whether green ultramarine is really a
chemical compound, and indeed it is now generally considered that the
colour is only due to small traces of sodium salts in very intimate
mechanical mixture with the blue variety, for by heating the green
body for some time at 160° with water in closed tubes, it is converted
into the blue product, and small traces of sodium compounds are found
in solution in the water; and further, on heating blue ultramarine
strongly with sodium sulphate and charcoal--that is, acting upon it
with sodium sulphide--the green variety is formed.
“In a paper by Knapp, an abstract of which appeared in the _Journal
of the Chemical Society_ for March 1880, there are some curious facts
recorded with regard to the colouring agent. It was noticed that when
silicic acid was replaced by boracic acid, a blue, nearly as stable in
its properties as that of ordinary ultramarine, was produced. It was
found that a blue could be obtained without alumina being introduced.
Hence silica without alumina, and alumina without silica, can be
employed with a certain amount of success. The blue, however, formed
without silica, is not so strong or stable as that formed with it.
“One very curious property which ultramarine possesses is its power of
giving up its sodium in exchange for other metals. Thus, by heating
blue ultramarine with a concentrated solution of silver nitrate
in sealed tubes to 120° for fifteen hours, a dark yellow _silver_
ultramarine is produced, containing about 46·5 per cent. of silver.
This corresponds to about 15·5 per cent. of sodium, which is just about
the amount that the original body contained.
“When this body is heated with an aqueous solution of sodium chloride
to 120° in sealed tubes, about three-quarters of the silver is replaced
by sodium, but the other quarter cannot be so replaced; in fact, blue
ultramarine, when heated with silver chloride, takes up silver, and
becomes green. But by heating silver ultramarine with sodium chloride
in the dry way, at rather a higher temperature, the whole of the silver
is replaced by sodium, but the ultramarine thus regenerated does not
equal the original body in colour. The change is probably due to the
loss of sulphur in the formation of the silver ultramarine.
“If in the above experiment potassium chloride be substituted for
the sodium salt, and the temperature not allowed to exceed 400°, a
bluish-green _potassium_ ultramarine is formed. _Barium_ ultramarine
is a yellowish-brown product, _zinc_ ultramarine is violet, and
_magnesium_ ultramarine is grey. These may all be obtained by acting on
the yellow silver ultramarine with the corresponding metallic chloride.
“From the experiments of Dollfus and Goppelsröder some very striking
differences have been brought to light between the three types of
colour which they examined--namely, the blue, green and violet--in
their behaviour with various reagents. Thus, an aqueous solution of
caustic soda or potash does not act on the blue or green, but turns
the violet to blue, and when heated with carbonic oxide the same result
ensues. Many other reagents have the same effect on the violet variety,
but when acted upon with sodium sulphide, the green turns grey, and
when heated with potassium chlorate becomes darker and loses its
brightness of colour. Dollfus and Goppelsröder attempt no explanation
of these facts, but simply state them as results of their observations,
and profess their inability to give any chemical formulæ for the three
ultramarines, though they consider that there is sufficient proof
that each has its distinct constitution. They give as their opinion,
however, that they are double silicates of aluminium and sodium, in
which a part of the oxygen is replaced by sulphur.
“Violet and red ultramarines are more bodies of scientific interest
than of any practical use, as their colouring power is not sufficiently
great. The violet variety may be prepared by exposing the underground
blue product to chlorine gas under a high temperature, while the
red may be obtained from the violet by acting on it, under a low
temperature, by dilute nitric acid fumes.
“The first artificial method of producing ultramarine was that known
as the ‘indirect process’--that is, first the manufacture of green
ultramarine; and secondly, its conversion into blue. It was carried out
as follows:--
“An intimate mixture of Glauber’s salts, china clay, and coal or rosin,
finely ground together, was placed in crucibles and baked or burned in
an oven for about six hours. It was then transferred to iron trays,
and heated with flowers of sulphur to the point where the sulphur took
fire, when it was allowed to burn itself out. By this second process
the green was converted into blue. It was then washed, ground with
water, and settled out, the first deposit being of a darker shade than
the second, and the colour becoming lighter as the powder settled was
finer in grind. This is essentially the method employed now at many
German works--those at Marienberg, for instance--and produces what is
known as “sulphate ultramarine,” distinguished by its pale shade and
almost _greenish_ blue tint.
“There are, however, some objections to the indirect process, and it
was considered advisable to find a plan by which ultramarine could be
made in bulk in a muffle furnace. The following is a method which is
employed at the present time in some of the German works:--
“A mixture of china clay, carbonate of soda, sulphate of soda, sulphur,
sand and charcoal or rosin, finely ground together, are placed upon
the floor of a muffle furnace, being pressed down so as to present an
even surface. The mixture is then entirely enclosed with fire-clay
tiles, the spaces between which are filled in with thin mortar. When
the oven is so charged, the front is built up, a small hole being left
for watching the temperature of the flue between the tiles and the top
of the furnace, and for drawing samples during the process, which is
done through a corresponding hole in the front of the fire-clay tiles,
temporarily closed with a fire-clay stopper. The oven is now heated,
slowly at first, and afterwards more strongly, so that at the end
of eight or nine hours it is at a dull red heat. It is kept at this
temperature for about 24 hours, when the heat is raised so that a clear
red glow is obtained, which is kept up to the end of the operation.
“For the purpose of taking a sample, an iron spoon borer is introduced
through the hole left in the enclosing tiles, turned round, and pulled
out. The contents are laid on a clean tile, and quickly covered with
another tile, on which a second quantity is placed, and allowed to
remain exposed to the air. If the oven has been sufficiently heated the
covered sample should appear of a bluish green, and no longer brown
or yellow, while the second sample should be rather bluer. If this be
the case, the oven is heated slowly for another hour, and then all
communication with the outer air is cut off. It is allowed to cool and
then opened, when the contents should appear as a beautiful blue mass,
the lower portion of which, however, is of a greenish tinge. Both parts
are now treated alike, but worked up separately, the greenish-blue
portion making an inferior article. The finishing process is as
follows:--
“The raw ultramarine is ground in upright mills, and then repeatedly
boiled for about ten or fifteen minutes at a time in cast-iron boilers,
being all the time agitated by a mechanical stirring arrangement. It
is then allowed to settle, and the water is drawn off with a siphon.
As soon as the powder settles into a hard compact mass, it has been
sufficiently washed, and it is then dug out. The part next to the
bottom of the boiler is generally coarse and of poor quality. It is
carefully separated from the upper portion, which is transferred to wet
mills of the ordinary description, and there ground for six to twelve
hours, during which time about 150 lb. can be treated in each mill.
The ground colour from these mills is then collected in a large tub,
and allowed to settle for four hours, during which time the coarsest
particles fall to the bottom. The liquid is then passed through a
series of tubs, in each of which it is allowed to stand for a period of
time, lengthening as the quality settled out becomes finer, the last
settling requiring about three weeks. The various qualities are then
dried and sifted, when they are ready for the market.
“The blue produced by this operation is of a good quality, but there
are some objections to the process, which have given rise to another,
in which the ultramarine is produced direct in crucibles similar to
those used in the indirect process.
“This is conducted as follows:--The mixture of raw materials consists
of about 100 parts of china clay, 90 of carbonate of soda, 110 of
sulphur, 20 of charcoal, and a quantity of infusorial earth, varying
according as the ultramarine produced is desired to be rich or poor in
silica. These are finely ground together, in which process great care
must be observed, as much depends upon its being properly carried out.
The mixture is then filled loosely into crucibles provided with flat
circular lids, which are fixed on with mortar containing clay. This
is allowed to dry, and the crucibles are then ready for firing, which
process is conducted in ovens, generally constructed so as to contain
several hundred crucibles, which are arranged in rows one above another.
“The mixture undergoes a very curious change of colour while in the
ovens. When put in it is greyish white, and during the process of
burning it becomes successively brown, green, blue, violet, red and
white, in the order named. These changes are, according to Guimet,
due to oxidation. The brown appears with the blue flames due to the
combustion of the sulphur, the green just after the sulphur flames have
ceased, and the blue is first formed at a temperature of about 700°--i.
e. a bright red heat. If, after this, heat be still applied and air
freely admitted, the mixture becomes first violet, then red or rose
coloured, and finally white. When this white body is heated to redness
with carbon or other reducing agents, the red, violet, blue, green and
brown colours (according to the amount of reducing agent employed) may
sometimes be reproduced, though the reaction is by no means a certain
one.
“If brown ultramarine be removed from the oven, and allowed to remain
exposed to the air, it immediately takes fire and burns to an inferior
blue colour. The same thing occurs with the green body. Even if the
brown product be completely cooled before being exposed to the air,
it will, as soon as the air is allowed to reach it, get hotter and
hotter, until it is glowing, when it will burst into flame and become
blue. Attempts have been made to preserve the brown colour, which is of
a beautiful chocolate tint, but have always failed. In one instance,
when this was tried, the colour was put immediately into water, and
treated like the ordinary blue variety, and as long as it was kept
moist no change was apparent. After being washed and wet ground the
moist powder was put into a cask, where for some time it was allowed to
remain undisturbed. At the end of about three weeks it was noticed that
the mass was hot, and on being turned out of the cask and broken up it
was found to be at a glowing heat in the interior.
“After the oven has been fired for several hours, it is carefully
closed at every point where air might enter, and allowed to cool
for four or five days. The exact length of time during which the
ovens are fired, and the amount of air admitted, depend upon various
circumstances, one important one being the state of the weather. Thus,
on a dull, foggy day, when the draught in the chimney is not good, a
longer time is required. Of course, no rule can be given for this,
and it is the experience required in the management of the oven that
makes the manufacture so difficult to carry out successfully, the early
efforts of a manufacturer not unfrequently resulting in the loss of
a whole ovenful of raw material. As soon as the oven has cooled, the
crucibles are taken out, and the contents of each are turned out in a
solid mass, which must be carefully cleaned with a knife of any badly
burned portions, and afterwards broken up and thrown into a cask along
with the contents of other crucibles.
“This forms what is known as crude raw ultramarine. It contains about
15 per cent. of sulphate of soda, which must be removed before the
colour is fit for sale.
“For this purpose it is washed with hot water in large tubs, after
which it is ground in wet mills to an impalpable powder, and allowed
to stand for about an hour in a large tub, in order to remove the
coarsest particles and dirt which are sure to be present. It is then
removed to another tub, where it settles for four or five hours, and
from this it passes to others, where it stands for various lengths of
time, increasing, of course, as the powder to be settled becomes finer,
the last settling occupying three or four weeks, and producing the
strongest quality that can be obtained--that is to say, it will bear
mixing with more of a reducing medium, such as mineral white, than
would a former settling for the mixture in each case to be of the same
depth of colour.
“The water, after the final settling, still contains about 5 per cent.
of ultramarine. This would take five or six months to settle, and
as this time could not generally be given to it, it is precipitated
with lime water, which has a sort of coagulating influence upon the
particles, which can then be removed by filtration. It is a curious
thing that this last quality is quite different from the one preceding
it, being very inferior in both colour and strength.
“After settling, all the various qualities are dried in kilns, and
sifted through fine brass wire sieves by means of a fan, which breaks
up the lumps and forces the particles through the meshes of the sieve,
which must be very close--about 100 to the inch--in order that the
ultramarine may be perfectly smooth and free from lumps or grit of
any sort. When finished, it should be in the form of an impalpable
powder--the finer qualities so fine, indeed, as to feel almost
_buttery_ when rubbed between the fingers. After this process the
different qualities and shades are mixed to certain standards, and are
then ready for sale.
“The uses of ultramarine in the arts and manufactures are very numerous
and important. The most important, from the point of view of quantity,
is the manufacture of ‘square blue’ for washing purposes. In the
preparation of this article the ultramarine is generally mixed with
bicarbonate of soda and some glutinous material, to help it to retain
its shape, and is then pressed into the well-known form of small square
or oblong blocks.
“It is also used largely in the manufacture of blue paint and printing
ink, and in the preparation of blue mottled soap. The way in which it
is employed in the last-named manufacture is worthy of remark. It is
added to the soap while it is in a molten state and just before it
is allowed to cool, and thoroughly mixed with it, so that the whole
mass is of a pale blue tint. If a small quantity of this be removed
from the boiler and cooled quickly, it remains of a uniform tint, but
in the case of the whole boilerful, where the cooling is very slow,
the action is entirely different. Just at the point of cooling, when
the soap is going to set hard, the ultramarine--to use a technical
expression--“strikes,” and goes into the form which gives to blue
mottled soap its well-known appearance.
“In the manufacture of paper, ultramarine also plays an important part.
It is here used not only for producing blue shades, but also as a
bleaching agent, to counteract the yellow when white paper is made.
“Another important use is in the calico manufacture, where it is used
both in the printing of blue patterns and in the finishing of goods. In
the case of calico printing, it is mixed with albumen and printed on to
the calico, which is then subjected to the action of steam, the albumen
being by this means coagulated and each grain of ultramarine surrounded
by an insoluble envelope, so that it cannot be washed out of the calico.
“The growth in the manufacture of ultramarine has been very remarkable,
especially when it is considered how little the process is understood
chemically, and what care and patience--to say nothing of the
equally important item of capital--are required in the starting of
a manufactory. Commencing less than 50 years ago in the works of
Guimet, at Lyons, who produced 120,000 lb. annually, there are at the
present day nearly 40 manufactories at work in various parts of the
world--chiefly in Germany--producing about 20 million lb. per year.
The following figures will give some idea of ten years’ growth of this
industry--from 1862 to 1872:--
1862. 1872.
Number of manufactories 24 32
Men employed 964 1929
Tons manufactured 3556 8585
“From the above numbers it will be seen that in these ten years the
manufacture more than doubled itself, the fact being due, however,
not so much to the increase in the number of works, which was only
one-third, as to the enlarged capabilities of those existing in 1862.
Thus, in the works of Dr. Leverkus, near Cologne--the first works ever
started in Germany--the number of men employed had, during these ten
years, more than doubled, while the output had trebled; and in the case
of the Marienberg Works the difference was even more striking, the
number of hands employed and the quantity turned out per annum having
nearly quadrupled.”
In reply to various questions which were asked in the discussion which
ensued, Mr. Rawlins said that, with regard to the use of ammonia
soda, it had frequently been used in the manufacture of ultramarine,
and was constantly used he understood, but he himself had not much
experience of it. As far as he could make out, it certainly produced
ultramarine, but of a darker shade than that made with Leblanc soda.
It could not be supposed, in works where the Leblanc soda was used,
that ammonia soda could conveniently be substituted, for of course
a works when established had to adhere to its known standards and
shades, and it would not do to change the raw materials, though the
ammonia soda produced a very good ultramarine. As regards the discovery
of ultramarine, the first works started anywhere were Guimet’s. He
had with him a little historical list containing the dates at which
the various works established before 1866 or a little later had been
started. It was drawn out by Hoffmann, who, as he stated before, was
the manager of large ultramarine works, and he put down Guimet’s,
which were started in 1829, first on the list. Dr. Leverkus started in
1834. He knew that the discovery of ultramarine had been attributed
to different people. He had mentioned Guimet because it had generally
been considered, as far as he had heard, that Guimet and Gmelin were
the two who discovered it from a manufacturing point of view. He had
heard of crystals of ultramarine, but had never seen any, and he knew
they were very difficult to prepare, and very rare. He had mentioned
that the grinding had to be done very thoroughly, because the better it
was mixed and the finer it was ground, the better was the ultramarine
produced. If it was badly mixed it was quite fatal to getting a good
result. Grinding lightens the colour. Raw ultramarine must be ground
before it was practicable to use it at all. For instance, a coarse
ultramarine could not be used for printing calico. Therefore it was
necessary to grind it both for the sake of the colour and for the
sake of the way in which it was applied. It was increased in value by
grinding because it made it stronger and finer. Before grinding it was
of a dark colour, but after grinding it became lighter and brighter.
The materials employed in McIvor’s process for making ultramarine
are kaolin or other suitable clay, a solution of sulphide of sodium,
in which sulphur in the form of flowers of sulphur is dissolved to
saturation, and caustic or carbonate of soda.
The preparation of the solution is effected by adding the sulphur to
boiling sulphide of sodium liquor of maximum strength until it ceases
to be taken up. The clay and soda are first roasted together at a red
heat, so as to effect a partial double decomposition, and the product,
after grinding, is made into a thick paste with “sulphur liquor,” i. e.
the sulphide of sodium solution of sulphur. This latter operation may
be carried out in an ordinary pug-mill. The paste so formed is dried in
an oven or other convenient way, and the dried mass (being broken into
small pieces) is roasted without access of air in a closed earthenware
retort, first at about 480°-570° F. for an hour, then at a red heat for
eight hours, and finally at a moderate heat just below dull redness,
in presence of a slow current of air, which enters through a series of
holes or small openings in the front of the retort, the current being
regulated by means of a damper or an adjustable slide. The retort
should be allowed to become quite cold before being opened, otherwise
the tint of the product will be injured.
McIvor has found the following proportions of the raw materials used in
the process to yield excellent results, viz:--
Sulphide of sodium 42 lb.
Sulphur 20 “
Kaolin (china clay) 110 “
Soda (as carbonate) 106 “
or
Caustic soda 40 “
These quantities yield about 2 cwt. of ultramarine blue.
The following communication from the pen of J. B. Nejedly, of Vienna,
appeared in the _Chemiker Zeitung_, during 1888:--
“Animated by various articles and notes in your journal under the
heading of ‘The Present Position of the Manufacture of Ultramarine,’
I would like to draw out of obscurity a little work on this industry
which contains much that is true, and furnishes at the same time many
comparisons with regard to the present position of the ultramarine
industry in Germany.
“The work above referred to was printed in the year 1840 and bears the
title:--
“‘Treatise on the chemico-technical preparation of Ultramarine
colours, according to the discoveries of Leykauf and Heyne, or on
the importance of the manufacture of blue and green Ultramarine for
purposes of science, art, and industry. By Friedr. Wilh. Heyne,
president of the Nürnberg Ultramarine Manufactory. Nürnberg: 1840.
Printed at the Campe Press.’
“The preface, which I consider to be well suited to present
circumstances, I reproduce verbatim, while from the little work itself
I will only quote such sentences as would seem to be suited to the
present time, and which are the most important as bearing on the
subject.
“‘_Preface._--The incitement to this treatise was furnished by the
utility of the discovery of Leykauf, instructor of chemistry at the
technical schools in Nürnberg, of artificially preparing the well-known
blue mineral colour styled ultramarine, according to simple principles,
which discovery was supplemented by the production of the green
ultramarine, an equally genuine and beautiful green mineral colour,
by the technist Heyne in Nürnberg. A short review of the importance
of these two discoveries for mankind in general and for science,
art, and industry in particular, will form the main subject of this
treatise, which has no other object but that of arousing the attention
of all high protectors and stimulators, as well as friends of industry
and art, to a newly-born industrial branch. At this moment we are
living in a period when many industries have got into the stocks,
in consequence of far too severe competition, combined with other
influences; indeed they are barely able to support those engaged in
them. If in consequence of this state of things it already becomes of
the most vital importance that fresh sources of acquisition should be
obtained, it becomes all the more so when by their means at the same
time materials come into requisition which the Fatherland possesses
in great superfluity, and which otherwise possess no intrinsic
value beyond just the expense of extracting them from their natural
localities or deposits, and the worth that attaches to their working up
for industrial purpose. A source of acquisition in this sense is met
with in the manufacture of blue and green ultramarine colours, which in
course of time can be raised to an extremely valuable acquisition. May
the communications here made result in their being considered worthy of
a thorough many-sided investigation and consideration.’
“REGARDING THE WORK ITSELF.
“Page 21.--‘Not long since a prize of 6000 francs was offered by the
“Société d’Encouragement.” This prize was gained by Guimet, who has not
published his process, and who now furnishes ultramarine at the price
of 25 francs per oz., whereas it otherwise cost 200 francs per oz.
Latterly, in 1839, Guimet reduced his price for ultramarine, viz. No.
1, for painting, to 10 francs, a lighter shade being 6 francs per oz.
In addition, this manufacturer furnishes lower qualities for carpet and
paper manufacturers at 20 francs and 12 francs per lb.’
“Page 23.--‘Indeed, if we are able to produce ultramarine by means of
a polysulphide of sodium and common clay, then the most beautiful and
most lasting of all known blue colours would at the same time become
the cheapest of them all.’
“Page 27.--‘All faults which are known to exist in the old methods are
obviated in the new invention of Leykauf and Heyne, while the same
offers the following advantages:--
“‘(1) The materials which are treated with it can be brought into use
without any special previous chemical preparations, indeed as supplied
by Nature, while chemical treatment is entirely unnecessary. In view of
the unimportant cost of derivation of the raw material, there cannot
consequently be any questions raised with regard to waste.
“‘(2) This method is so simple that any man of sound intellect can
easily work it, without possessing any special chemical knowledge
beforehand. As the labour can be easily grappled with, errors can only
occur when the grossest carelessness is shown in conforming to the
instructions prescribed.
“‘(3) According to the said method one can work according to any
desired scale, and, what is best of all, the larger this scale the more
favourable are the results obtained, lighter work and excellence of
quality.
“‘(4) If the process is carefully conducted, everything is in your own
power, nothing depending on chance.
“‘(5) Consequently an equal product can invariably be obtained, while
this can at will be brought to the most complete stage of perfection
at but little greater cost than lower qualities entail.
“‘(6) According to this method you are master of the fire, enabling a
retention of colours in any desired shade, of the deepest tone, of the
greatest permanency.
“‘From this it appears: That this process is the easiest, the cheapest,
and the most complete. Worked according to this method the hope is
likely soon to become a reality that ultramarine may yet become the
cheapest of all mineral colours, and as in the same everything rests
upon simplicity, the preparation of the article in future will be
carried on somewhat after the fashion of baking, brewing, &c.’
“Page 32.--‘Moreover, there is not only blue ultramarine, but also a
pure green, and we may venture the hope that similar combinations in
white, black, red, and yellow will soon follow in equal perfection.
In consequence of these discoveries, Leykauf and Heyne have erected a
factory in Nürnberg, which, according to a circular dated 15th July,
1840, is in operation under the style of “Leykauf, Heyne and Co.,” and
are producing the two ultramarine colours referred to at the present
time at the rate of 50 lb. per day.’
“Page 33.--‘All the mechanical appliances of the factory are at the
present time exclusively worked by hand, the number of persons employed
being sixteen; while the establishment upon completion of the buildings
that are wanting is calculated to employ twenty operatives and two
horses. With this extension the factory will be able to turn out 5
cwt. blue and 5 cwt. green weekly, consequently annually 500 cwt. of
finished merchantable ultramarine will be brought on the market.’
“Page 35.--‘Now, as regards the prices ruling at present for Nürnberg
ultramarine, these are, as compared with those of the French, more than
500 per cent. cheaper. Blue ultramarine costs, namely, in Nürnberg,
quality No. 0, 10 florins per lb.; a lighter quality, which is
nevertheless darker than the darkest French at 100 francs, 5 fl. per
lb.; a third quality likewise darker than the seconds French at 60
francs, 3 fl. per lb. Green ultramarine, 3 fl. 10 kr. per lb.
“‘How much further, however, these low prices will be yet reduced
after the completion of the factory, may be gathered from a detailed
calculation of cost which the chief of this factory has made himself
responsible for as being the highest estimate. This calculation of
cost is based upon the weekly production of 10 cwt., which the factory
will soon be able to turn out, and upon a necessary cost of plant and
working capital of 90,000 Rhenish florins, as follows:--
“Page 36.--‘Calculation of cost of 500 cwt. blue and green
ultramarine:--
Fl.
(1) Raw material and cost of transport 10,000
(2) Fuel, including cost of transport of 7200 cwt. of
coal at fl. 1.30 10,800
(3) Wages of 20 operatives at fl. 250 per annum 5,000
(4) Utensils and apparatus 3,200
(5) Buildings and repairs 3,400
(6) Keep for two horses 600
(7) Expense of factory 3,000
(8) Cost of administration 2,000
(9) Unforeseen matters and accidents 2,000
(10) Interest on building and working capital at 5
per cent. 4,500
(11) Public taxes, insurance, &c. 500
------
Thus 500 cwt. will cost Fl. 45,000
“ 1 “ “ Fl. 90
“ 1 lb. “ 45kr.
“‘Forty-five kreutzers, therefore, in accordance with the above, will
in future be the production cost of a colour which, as is well known,
could not be obtained for several hundred guldens, while in green it
was not procurable at any price.’
“I venture to hope that the foregoing communication may yet prove of
some interest in chemical circles.”
1 florin or gulden = 2_s._ 1 kreutzer = ½_d._
Ultramarine is by far the most commonly used of the blue pigments.
It is a chemical combination of silica, alumina, soda, and sulphur,
but its exact chemical constitution is not known, the proportions of
its ingredients varying somewhat with different makes. There are two
principal varieties of ultramarine sold. One is known as sulphate
ultramarine the other as soda ultramarine, from the materials used in
the process of manufacture. In the first, silica, china clay, _sulphate
of soda_, and coal are used; in the latter, silica, china clay,
_carbonate of soda_, and sulphur are used. The sulphate ultramarine is
distinguished by its very pale greenish blue colour, while the soda
ultramarine is of a violet hue.
Ultramarine is distinguished from other blues by the fact that acids
completely decolorise it, with the evolution of sulphuretted hydrogen
and the formation of a white precipitate of sulphate.
The sulphate ultramarine is more easily decomposed by acids than
the soda ultramarine, and some makes of the latter more easily than
others. Alkalies and heat have no action on this pigment. Boiled in
strong nitric acid, ultramarine is completely decolorised, a colourless
solution being formed, and a gelatinous mass of silica being left as a
residue.
It is not as a rule necessary to make an analysis of the pigment; the
above tests serve to distinguish it from other pigments.
An assay of ultramarine should include the following points:--1st,
colour or tint; 2nd, covering power or body; 3rd, acid resisting
properties: this can be tested by making a very weak solution of
sulphuric acid--about 4 oz. in 1000 oz. of water--and adding a little
of this to the pigment contained in a glass, and noting how long it
takes to bring about decolorisation; 4th, the power of resistance to
the action of alum. When ultramarines are boiled with a solution of
alum, they are more or less reddened thereby; those which are made
with a large excess of silica are found to resist this action of
alum better than those containing a normal quantity of this compound.
Such ultramarines are preferred by the paper maker, who uses a large
quantity of alum and sulphate of alumina in the sizing of his papers,
and therefore he wants an ultramarine which shall not change in shade
when used for tinting alumina sized papers. This point is easily
tested. A solution of alum is made, and in a little of this a small
quantity of ultramarine is boiled for a few minutes, and it is noted
whether any change of shade occurs. If any sample is found to change
much, that sample must be rejected for paper tinting, although it may
be used by the painter or the laundress.
It may be worth pointing out here that ultramarine should not be used
with any other colours which have a tendency to be acid, as sooner or
later the colour will be destroyed. It should also not be used with
lead or copper pigments, as the sulphur it contains tends to react on
those metals; forming the black sulphides, thus leading to the ultimate
discoloration of the mixture.--(_Chemical Trade Journal_).