The elements of cyanogen, combined with sulphur, form a salt radical,
sulphocyanogen, C_{2}NS_{2}, which is expressed by the symbol Csy. The
sulphocyanide of potassium, KCsy, is prepared by fusing ferrocyanide of
potassium, deprived of its water of crystallization, intimately mixed
with half its weight of sulphur and 17 parts of carbonate of potassa. The
molten mass, after having cooled, is exhausted with water, the solution
evaporated to dryness, and extracted with alcohol, from which the
crystals of the salt are separated by evaporation.
It is also made by melting the ferrocyanide of potassium with sulphide of
potassium. It is a white, crystallizable salt of a taste resembling that
of niter, soluble in water and alcohol, and extremely poisonous. It
dissolves the chlorides, iodides, and bromides of silver, is, therefore,
a fixing agent, but has not come in general use as such. Vogel speaks
highly of it as an addition to the positive toning bath, although he
prefers the analogous ammonium salt in the following formula:
Chloride of gold solution.... (1:50) 3 c. cm. (46-1/5 grains).
Sulphocyanide of ammonium ... 20 grammes (308 grains).
Water........100 c. cm. (3 ounces 5 drachms 40 grains).
_Ferrocyanide of Potassium_--K_{2}Cfy+3HO, or K_{2}C_{8}N_{3}Fe+3HO, is
generally known by the name of yellow prussiate of potassa. It contains
ferrocyanogen, a compound radical, consisting of 1 eq. of metallic iron
and 3 eq. of the elements of cyanogen, and is designated by the symbol
Cfy.
The potassium salt is manufactured on a large scale from refuse animal
matter, as old leather, chips of horn, woolen rags, hoofs, blood (hence
its German name, "Blutlaugen salz"), greaves, and other substances rich
in nitrogen, by fusing them with crude carbonate of potassa and iron
scraps or filings to a red heat, the operation to go on in an iron pot or
shell, with the exclusion of all air. Cyanide of potassium is generated
in large quantities. The melted mass is afterward treated with hot water,
which dissolves the cyanide and other salts, the cyanide being then
quickly converted by the action of oxide of iron, formed during the
operation of fusing, into ferrocyanide. The filtered solution is
evaporated, crystallized, and recrystallized. The best temperature for
making the solution is between 158 and 176 deg. F. The conversion of the
cyanide into the ferrocyanide is greatly facilitated by the presence of
finely divided sulphuret of iron and caustic potash. Some years ago this
salt was manufactured by a process which dispensed with the use of animal
matter, the necessary nitrogen being obtained by a current of atmospheric
air. Fragments of charcoal, impregnated with carbonate of potassa, were
exposed to a white heat in a clay cylinder, through which a current of
air was drawn by a suction pump. The process succeeded in a chemical
sense, but failed on the score of economy.
Richard Brunquell passes ammonia through tubes filled with charcoal, and
heated to redness so as to form cyanide of ammonium, which is converted
into the ferrocyanide of potassium by contact with potash solution and
suitable iron compounds. Ferrocyanide of potassium is in large beautiful
transparent four-sided tabular crystals, of a lemon-yellow color, soluble
in four parts of cold and two of boiling water, insoluble in alcohol.
Exposed to heat it loses three eq. of water, and becomes anhydrous; at a
high temperature it yields cyanide of potassium, carbide of iron, and
various gases. This salt is said to have no poisonous properties,
although the dangerous hydrocyanic acid is made from it. In large doses
it occasions, however, vertigo, numbness, and coldness. It is used in
various photographic processes. Newton employs it in combination with
pyrogallol and soda in the development of bromo-gelatine plates.
The ferri or ferrid cyanide of potassium discovered by Gmelin is often,
but improperly, termed red prussiate of potash. It is formed by passing a
current of chlorine gas through a solution of ferrocyanide of potassium
until the liquid ceases to give a precipitate with a salt of sesquioxide
of iron, and acquires a deep, reddish-green color. The solution is then
evaporated, crystallized, and recrystallized. It forms regular prismatic
or tabular crystals, of a beautiful ruby-red tint, permanent in the air,
soluble in four parts of cold water. The crystals burn when introduced
into the flame of a candle, and emit sparks.
The theory of the formation of this salt is, that one eq. of chlorine
withdraws from two eq. of the ferrocyanide of potassium, one eq. of
potassium, forming chloride of potassium, which remains in the mother
liquid. The reaction is explained by the following equation:
2(K_{2}Cfy)+Cl=K_{3}Cfy_{2}+KCl.
The radical ferridcyanogen, isomeric[2] with ferrocyanogen, is supposed
to be formed by the coalescence of two equivalents of ferrocyanogen, and
is represented by the symbol Cfdy; accordingly the formula of
ferridcyanide of potassium is K_{3}Cfdy.
[Footnote 2: Isomeric bodies, or substances different in properties yet
identical in composition, are of constant occurrence in organic
chemistry, and stand among its most peculiar features.]
Ferridcyanide of potassium has found extensive application in
photographic processes for intensifying negatives; those of Eder, in
combination with nitrate of lead, or Selle's, with nitrate of uranium;
Ander's blue intensification of gelatine negatives, Farmer's process of
reducing intensity, the coloring of diapositives, the very important blue
printing, and various others, are daily practiced in our laboratories.
The ferrocyanide of potassium is a chemical reagent of great value,
giving rise to precipitates with the neutral or slightly acid solutions
of metals, like the beautiful brown ferrocyanide of copper, and that of
lead. When a ferrocyanide is added to a solution of a sesquioxide of
iron, Prussian blue or ferrocyanide of iron is produced. The exact
composition of this remarkable substance is not distinctly stated, as
various blue compounds may be precipitated under different circumstances.
Berzelius gives the following account: 3 eq. of ferrocyanide and 2 eq. of
sesquioxide of iron are mutually decomposed, forming 1 eq. of Prussian
blue and 6 eq. of the potassa salt, which remains in solution, or
3K_{2}Cfy + 2(Fe_{2}O_{3}3NO_{3}) = Fe_{4}Cfy_{3} + 6(KO,NO_{5}). It
forms a bulky precipitate of an intense blue, is quite insoluble in water
or weak acids, with the exception of oxalic acid, with which it gives a
deep blue liquid, occasionally used as blue ink.
Ferridcyanide of potassium, added to a salt of the sesquioxide of iron,
yields no precipitate, but merely darkens the reddish-brown solution;
with protoxide of iron it gives a blue precipitate, containing
Fe_{3}Cfdy, which is of a brighter tint than that of Prussian blue, and
is known by the name of Turnbull's blue. Hence, the ferridcyanide of
potassium is as excellent a test for protoxide of iron as the yellow
ferrocyanide is for the sesquioxide.--_E., Photo. Times_.
* * * * *
FOUCAULT'S APPARATUS FOR MANUFACTURING ILLUMINATING GAS AND
HYDROGEN.
The illuminating gas and hydrogen apparatus, illustrated herewith, is
adapted to all cases in which it is desirable to manufacture gas upon a
small scale.
Through the use solely of oil or water, it produces illuminating gas or
pure hydrogen for all the applications that may be required of them. It
consists of three parts, viz., of a vaporizer, A, which converts the
liquids into gas; of a distributer, B, which contains and distributes the
liquids to be converted into gas, and of a regulator, C, which
automatically regulates the flow of the liquids in proportion as they are
used.
[Illustration: FIG. 1.--FOUCAULT'S GAS APPARATUS.]
In the vaporizer Mr. Foucault, the inventor of the apparatus, obtains a
perfectly regular combustion through the use of a central column, 15,
charged with fuel, closed at the upper part, open beneath, and entering a
furnace that is fed by it with regularity, the zone of combustion not
being able to extend beyond the level of the draught. The grate, 16, is
capable of revolving upon its axis in order to separate the cinders. It
also oscillates, and is provided with jaws for crushing the fuel; and it
may likewise be lowered so as to let the fire drop into the ash-pan when
it is desired to stop operations.
The vaporizer, properly so called, is not placed directly over the fire,
and for this reason the production of a spheroidal state of the liquid is
avoided. It consists of a vessel, 44, into which the liquid is led by a
pipe, 43. The cast-iron evaporating vessel, 14, is provided with
appendages, 14 _bis_, which dip into the liquid and bring about its
evaporation. A refractory clay sleeve, 41, protects the lower part of the
cylinder, 15, from the fire, and diminishes the smoke passages at 42. The
vapor produced makes its way vertically through a layer of charcoal
placed between the evaporating vessel, 14, and the receiver, 17, and
serving to decompose the aqueous vapor formed.
All clay and red and white lead joints are done away with in this part of
the apparatus, as are also packing bolts. Thus, at the upper part the
cover, 19, is provided with a rim that enters a cavity filled with lead,
so, too, the lower part of the evaporating vessel, 14, rests in a channel
containing lead. There is also at 30, a joint of the same character for
the rim of the external cylindrical vessel, 18. Both this latter and the
receiver, 17, dip beneath into a tank of water, 66.
The distributer, B, is so arranged as to cause the water, and oil, and
the liquids to be vaporized to flow with the greatest regularity, and
proportionally to the consumption of the gas in cases where the latter is
not stored up in a gas meter. The flow is controlled by cocks that are
actuated by variations in the height of the regulator receiver. All the
condensation that occurs in the various parts of the apparatus collects
in a receptacle, 52, so arranged as to perform the office of a separator
and set apart the oil at 20, and the water at 21, through the natural
effect of their difference in density. This latter is likewise utilized
for causing the oil to flow into the vaporizer through 26 and 27, instead
of using a graduated cock that receives a variable pressure from the
receiver. In this way every cause of obstruction is avoided.
[Illustration: FIG. 2.--SECTION.]
We have stated that the regulator, C, serves to automatically regulate
the flow of the liquids proportionally to the consumption of the gases
produced. To effect this a communication is established between the
regulator receiver, 59, and the aperture through which the liquids flow,
and the flow is thus modified by the valves, 54 and 55.
The water contained in the reservoir of the regulator serves to wash the
gas which enters through a number of orifices in the disk, 60, this
latter being fixed beneath the level of the water. The gas may be
purified by dissolving metallic salts in the water.
By means of the arrangement above described, there may be manufactured at
will a rich gas from liquid hydrocarburets, hydrogen from water, and gas
obtained by an admixture of two others simultaneously produced and
combined in the apparatus.--_Chronique Industrielle._
* * * * *