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as its vapor density proves, double the proportions of carbon and hydrogen
existing in olefiant gas. It was obtained by Faraday as one of the products
of the destructive distillation of oil. He called it bicarburetted hydrogen.
As a gas, it has a sp. gr. of 1'9264 ; it burns with a brilliant, white, smoky
flame. It is not dissolved by water, but is soluble in alcohol and the oils.
When cooled to zero, it is condensed into a colorless, light liquid, having a
sp. gr. of 0-627.

CARBON AND NITROGEN. These elements cannot be made to combine
directly, but they form three different compounds ; a gaseous body, cyano-
gen, NC a ; and two solids, paracyanogen, N a C 4 , and mellone, N 4 C 6 .



2T8 CYANOGEN. CHEMICAL PROPERTIES.

CYANOGEN (NC 3 , or Cy=26). Bicarburet of Nitrogen. This gaseous
compound was discovered, in 1815, by Gay-Lnssac, and termed cyanogen
(from xvarof, bhie, and ytwdu, to generate), in consequence of its being essen-
tial to the production of Prussian blue. It is sometimes formed by the
direct action of nitrogen upon carbon in the presence of bases, as where
nitrogen or air is passed over a mixture of charcoal and carbonate of potassa,
heated to redness. Under these circumstances, cyanogen is produced, and
enters into combination with the metal potassium (KO,C0 2 4-C 4 -fN=K,NC 3
-f SCO). Cyanide of potassium is thus sometimes produced and deposited
in the crevices of the walls of blast-furnaces. When an organic substance
containing nitrogen and carbon is heated, these elements will not unite
directly; but if heated with the alkaline metals, potassium or sodium, in a
glass tube, out of contact of air, they instantly combine to form cyanogen,
and this body unites with the metal, to produce a metallic cyanide. This
conversion has already been described as one of the best methods of detect-
ing nitrogen in organic matter (p. 156). In the destructive distillation of
coal, the nitrogen and carbon combine to form cyanogen, which is found in
the solid products in combination with ammonia arid lime. Sulphocyanogen
is also produced under these circumstances, as the cyanogen combines with
a portion of the sulphur of coal.

Preparation. Cyanogen may be obtained in the gaseous state by heating
well-dried cyanide of mercury in a small retort to dull redness. The gas
readily comes over, and, as it is dissolved by water, it should be collected,
and preserved over mercury. Although cyanogen and mercury are both
volatile bodies, it is impossible to obtain more than one-third of the cyano-
gen present in the cyanide [3HgCy ==NC a ( cyanogen) + N 4 C 4 (paracyanogen)
-f 3Hg]. Mercury sublimes, but there remains in the retort a brownish-
black, spongy-looking solid, which from its composition has been called para-
cyanogen. It is equivalent to two atoms of cyanogen, and is polymeric with
it (2NC 3 =N 2 C 4 ). When strongly heated in air, this residue yields carbonic
acid, and leaves CN ; but it is very difficult of combustion. Cyanogen is so
easily decomposed by the elements of water, that- great care should be taken
to dry the cyanide of mercury thoroughly before it is submitted to heat ; and
no moisture should be present in the jars in which the gas is collected.

Properties. Cyanogen is a colorless neutral gas, of a pungent odor, irri-
tating to the eyes, and highly poisonous if breathed even in a diluted state.
Its specific gravity when compared with hydrogen is as 26 to 1 ; and with
common air, as 1*796 to 1; 100 cubic inches weigh 55 -64 grains. It sustains
a high temperature in porcelain tubes without decomposition. Under a
pressure of between three and four atmospheres at the temperature of
45, Faraday condensed cyanogen into a limpid colorless liquid, of a specific
gravity of about 0'9, and a refractive power rather less than that of water.
When a tube containing it was opened, the expansion within appeared incon-
siderable, and the liquid slowly evaporated, producing intense cold. It
does not conduct electricity. At temperatures below 30, it becomes a
transparent crystalline solid.

It extinguishes a lighted taper, but takes fire and burns with an inner
ose-red flame, surrounded by a blue flame. As it is very heavy, the jar
should be slightly inclined for its complete condensation, or water should be
poured into the jar while it is burning. Carbonic acid and nitrogen are the
sole products of this combustion. Four equivalents or two volumes of
oxygen are required for its entire combustion (NC 3 +0 4 =2CO a +N). In
these proportions the mixture is explosive by heat or electricity. A red-hot
platinum wire, or the electric spark, will kindle the gases instantly. The
production of carbonic acid as a result of its combustion, maybe proved by



COMPOUNDS OF CYANOGEN. 279

burning the gas from a jet under a jar of air, and subsequently adding lime-
water to the contents of the jar. All ordinary combustibles are extinguished
in it. Alkaline metals may, however, be burnt in it as readily as in chlorine.
Potassium or sodium heated to ignition and introduced into the gas, under-
goes vivid combustion, and the cyanogen combines directly with the metal to
form a metallic cyanide. It is this property of entering into combination
like an element, and the fact that with hydrogen it forms a hydracid in every
respect analogous to those produced by the halogens, which have induced
chemists to designate cyanogen as a compound radical, and to associate it
with chlorine, bromine, and iodine. Its existence shows that a body may
have all the ordinary chemical properties assigned to an element, and yet be
of a compound nature.

Cyanogen does not bleach organic colors. Water will dissolve 4*5 volumes
of the gas; alcohol will dissolve 23 volumes; and it is also taken up by
ether and oil of turpentine. Its aqueous solution is rapidly decomposed
by exposure to light ; it acquires at first acid and afterwards alkaline pro-
perties, cyanic acid and ammonia being products of this reaction. Oxalate
and carbonate of ammonia, formate of ammonia, urea, and paracyanogen, are
also products, in different stages of decomposition, of the aqueous solution.
Iodine, sulphur, and phosphorus may be sublimed in the gas without change.
Dry chlorine has no action on dry cyanogen ; but when moist and .exposed
to light, a yellow oil is produced, which appears to be a mixture of chloride
of carbon arid chloride of nitrogen (SERULLAS), furnishes another proof of
the importance of water to bring about chemical changes in bodies (see pages
42 and 145).

The gas is readily dissolved by alkaline liquids ; and, as with the halogens,
a cyanate of the alkali and cyanide of the metal are produced. Oxide of
mercury in a humid state, also absorbs the gas, forming a soluble cyanide.

Composition. Cyanogen may be passed through a porcelain tube intensely
heated without undergoing any change ; but if passed through a red-hot iron
tube, carbon is deposited, and a volume of nitrogen* equivalent to the cyanogen
employed, is set free. If one volume of this gas is mixed with two volumes
of oxygen, and the mixture is detonated by the electric spark over mercury,
two volumes of carbonic acid and one volume of nitrogen result; hence,
deducting the oxygen employed, each volume of this gas must consist of two
volumes of carbon vapor, and one volume of nitrogen condensed into a single
volume of the gas.

Atoms. Weights. Per cent. Vols. Sp. Gr.

Nitrogen . . 1 ... 14 ... 53-85 ... 1 ... 0-9674
Carbon . . 2 ... 12 ... 46-15 ... 2 ... 0-8292

1 26 100-00 1 1-7966

Test. The colored flame of the gas during combustion, and an examina-
tion of the products, carbonic acid and nitrogen, are sufficient to identify it.

Compounds. Cyanogen combines directly with metals, like an element,
forming cyanides of metals analogous to oxides and chlorides ; it forms acids
with oxygen and hydrogen, and compound radicals with sulphur and iron,
which also combine with hydrogen to form acids, and with metals to form
peculiar classes of salts. The metallic cyanides are remarkable for the readi-
ness with which they produce double salts. The subjoined list comprises the
principal derivative compounds of cyanogen : .



280 CYANIC ACID. CHEMICAL PROPERTIES.

Cyanogen Cy Cyanide MCy

Cyanic acid Cy, Cyanate

Fulminic acid Cy 2 ,0 2 Fulminate

Cyanuric acid Cy 3 .0 3 Cyanurates Cy 3 3 ,3MO

Hydrocyanic acid HCy + MO = Cyanide MCy,(HO)

f H Hydrosulpliocyanic acid
Sulphocyanogen b 2 0y | M Siilphocyanide

J H 2 Hydroferrocyanic acid
Ferrocyanogen *eLy 3 \ M 3 Ferrocyanide

( H 3 Hydroferricyanic acid
Ferricyanogen *e 2 Cy 6 \ M 3 Ferricyanide

f H, Nitrohydrocyanic acid
Nitroferricyanogen Fe 2 Cy 5 N0 2 { M* Nitroprusside

MELLONE (N 4 C fi ). The third compound of carbon and nitrogen is a solid
substance of a yellow color, produced in the destructive distillation of sul-
phocyanogen. It may be heated to dull redness without change, but at a
higher temperature it is resolved into three volumes of cyanogen and one of
nitrogen (N 4 C 6 =3NC 2 4- N). It is a compound radical, and combines directly
with metals to form Mellonides. According to Gerhardt, it always contains
hydrogen.

CYANOGEN AND OXYGEN. These bodies form three homologous acids,
the cyanic (CyO), the fulminic (Cy 2 2 ), and the cyaimric (Cy 3 3 ). They
are monobasic, bibasic, and tribasic, respectively.

CYANIC ACID (CyO). When cyanogen is passed into an alkaline solution,
a cyanide and a cyanate are formed (2BaO-f-2Cy=BaCy-f BaO,CyO), and
so far the action of cyanogen corresponds to that of chlorine : but the ex-
treme tendency of the cyanates so formed, to decomposition, prevents their
separation. A permanent cyanate may be obtained by the following process:
six parts of ferrocyanide of potassium and two of carbonate of potassa,
both carefully dried (anhydrous), are intimately mixed in fine powder with
eight parts of pure and dry peroxide of manganese: this mixture is heated
for some time to dull redness, until a portion cooled and dissolved in water,
does not give a blue precipitate with a persalt of iron. The contents of the
crucible are then allowed to cool, reduced to powder, and boiled for fifteen
minutes in alcohol, sp. gr. '850. The liquid is filtered while hot, and on cooling
it deposits crystals of cyanate of potassa. The alcohol is poured from the
salt and again boiled with the residue, so long as further portions of cyanate
can be thus obtained. The salt should be well dried by pressure in filtering
paper, and afterwards in vacua over sulphuric acid; it must be preserved out
of contact of air and moisture, otherwise it will soon pass into ammonia and
carbonate of potassa. Although the cyanic acid may thus be obtained in
union with a base, any attempt to set it free by means of another acid, is
attended by its immediate decomposition into carbonic acid and ammonia.
Wohler endeavored to procure the acid in a pure state, by decomposing
cyanate of silver by dry hydrochloric acid. The product, however, was hy-
drated cyanic acid with one equivalent of hydrochloric acid gas ; hence,
when brought into contact with water, it was immediately resolved into
hydrochlorate of ammonia and carbonic acid. Cyanic acid, in the presence
of water, cannot be separated from its salts without undergoing immediate
decomposition. Liebig found that it might be procured in a concentrated
form as hydrate, by heating cyanuric acid in an air-tight retort, connected
with a receiver surrounded by ice. These acids contain the same elements,
and are mutually convertible the one into the other ; but cyanic acid is a
simple atom, while cyanuric acid is a complex atom.

Properties. This acid in its concentrated state (HO, CyO) is a limpid
colorless liquid. It is intensely corrosive and strongly acid. Its vapor is



FULMINIC ACID. 281

very pungent, like that of the strongest acetic acid, and U is very irritating
to the eyes and nose ; but it is not inflammable. When diluted with a little
water and retained at 32, its odor is like that of acetic acid, but it soon*
begins to change ; carbonic acid is evolved, carbonate and cyanate of ammo-
nia are formed, and, by evaporation, crystals of urea may be obtained. In
this case one atom of cyanic acid and three of water, at first yield one atom
of bicarbonate of ammonia; C 2 N,O-f 3HO=NH 3 ,2C0 3 : but the cyanic,
being a stronger acid than the carbonic, the undecomposed cyanic acid com-
bines with the ammonia and expels carbonic acid ; and, on evaporation, the
cyanate of ammonia combines with an atom of water to form urea ; NH 3 ,



Hydrated cyanic acid, as obtained by the method above described, when
it has cooled to 60, becomes turbid and milky-looking ; it acquires heat
spontaneously, begins to boil, and then passes into a pasty-looking solid,
while there are sudden evolutions of gas with explosions, from the unchanged
portion of the acid. It is ultimately converted into a dry, solid, uncrystal-
line white substance, which is called Cyamelide (LiEBiG). These remarkable
changes take place rapidly at the common temperature, and quite independ-
ently of air and moisture. They also take place at the freezing-point, but
more slowly, and no gas is evolved under these circumstances.

Cyamelide is insoluble in water, nitric acid, and hydrochloric acid, either
separately or mixed as aqua regia. It is dissolved by potassa with evolution
of ammonia, and cyanurate of potassa is obtained by evaporation. Concen-
trated sulphuric acid dissolves it when the mixture is moderately heated, with
escape of carbonic acid and the production of sulphate of ammonia. The
products of its decomposition are therefore the same as those of cyanic acid
in water, and when cyamelide is distilled by itself it is reconverted into hy-
drated cyanic acid. It is therefore an isomeric solid condition of this acid.

Cyanates. The cyanates of the alkalies alone are soluble in water, and
are not decomposed by a red heat. When an aqueous solution of an alkaline
cyanate is heated, carbonic acid and ammonia are produced (NC ? 0-|-3HO =
NH 3 +2CO,j). The nitrates of lead, silver, and mercury give with the solu-
tion of a cyanate white precipitates. When mixed with sulphate of ammonia,
and evaporated to dryness, a solution of a cyanate yields urea. When hy-
drated cyanate of ammonia is gently heated either in the dry state or in solu-
tion, it is converted into urea (Wohler). These substances are metameric
(see page 19). When an acid is added to a cyanate, either solid or in solu-
tion, there is effervescence, owing to the production and escape of carbonic
acid. The strong pungent odor of hydrated cyanic acid will be perceptible,
and a salt of ammonia is formed in the liquid. Hence a cyanate cannot be
mistaken for a carbonate.

FULMINJC ACID 2(C 3 N)0 3 or (Cy 3 2 ). Under the articles MERCURY and
SILVER, the process for preparing detonating compounds of these metals, by
acting upon their nitric solutions by alcohol, will be described. The oxides
are united to an acid containing the same elements, and in the same relative
proportions, as the cyanic acid, to which, in that particular state of combi-
nation, the term Fulminic Acid has been applied ; but the equivalent of the
fulminic acid is exactly double that of the cyanic. This acid has not been
isolated : it is known only in combination with bases.

Fulminic acid, therefore, cannot be obtained as such from the bases with
which it is combined ; at the moment of its separation by a stronger acid,
it is resolved into hydrocyanic acid and other products. Hence we have in
this compound an acid in which, the metal cannot be replaced by hydrogen
(see page 75).

Fulminates. These are bibasic salts containing either two atoms of fixed



282 CYANOGEN AND HYDROGEN. HYDROCYANIC ACID.

base (neutral ful initiates), or one atom of fixed base and one atom of water.
The two atoms of fixed base may be represented by two atoms of the oxide
of an easily reducible metal, or by two atoms of the oxides of two different
metals, also easily reducible. There are no fulminates of two alkaline bases.
The fulminates explode by concussion, friction, heat, or contact with concen-
trated sulphuric acid. They evolve hydrocyanic acid when treated with
hydrochloric acid.

CYANURIC ACID (C 6 N 3 3 or Cy 3 3 ). This acid may be obtained in com-
bination with three atoms of water, as 3HO-f-Cy 3 3 . Scheele first described
it under the name of pyro-uric acid. He procured it by the destructive dis-
tillation of uric acid. It exists in the hydrated and anhydrous states. It
is dissolved by strong sulphuric or nitric acid without change, and is pre-
cipitated by water. The alkaline cyanurates evolve, when heated, hydrated
cyanic acid, cyanate of ammonia, carbonic acid, and nitrogen, leaving a
residue of cyanate.

The cyanic, fulminic, and cyanuric acids, although composed of similar
proportions of the same elements, are widely different in properties a fact
which appears to show that, in compounds of a quasi-organic character, the
properties of bodies are more dependent on molecular arrangement than on
atomatic constitution. The cyanuric acid alone can exist in the anhydrous
state, and remain unchanged in contact with water and other acids. This
acid alone is soluble in alkalies without change, and may be separated from
its alkaline solution by acids in an unaltered state. Cyanurate of silver will
bear a temperature of 300, without undergoing decomposition. At this
temperature, cyanate of silver is decomposed with ignition and evolution of
carbonic acid and nitrogen (LiEBiG), while fulminate of silver under the
same circumstances is decomposed with detonation, a double amount of car-
bonic acid and nitrogen being produced. Although fulminic acid is the
intermediate compound, it cannot be procured either by the intermixture of
the cyanic and cyanuric acids, or by the action of any chemical reagents
upon them. In this respect these three compounds somewhat resemble the
hydrates of phosphoric acid, the first being converted at once into the third,
without the production of the second hydrate (p. 242). In phosphoric acid,
the difference arises from an increase in the atoms of water of hydration : in
these acid compounds of cyanogen, the first and last members of the series
only are hydrated ; and there is an increase in the proportion of the elements
as well as of the atoms of water. In reference to fulminic acid, it is worthy
of note that, as in an isolated state, it will not combine with the elements of
water, its existence proves, among other facts, that acids are not necessarily
salts of hydrogen (see p. 94).

CYANOGEN AND HYDROGEN. HYDROCYANIC ACID. Cyanhydric Acid.
Prussia Acid.(R,NG 2 or HCy) This compound was first obtained by
Scheele in 1782. It was not, however, until the discovery of cyanogen by
Gay-Lussac, in 1815, that its real nature was understood, and its compo-
nents accurately determined. Cyanogen and hydrogen have no tendency
to direct combination, but by the action of certain acids on metallic cyan-
ides, hydrocyanic acid is produced by double decomposition : in this way it
is obtained by the action of hydrochloric acid on dry cyanide of mercury or
silver (AgCy4HCl=AgCl + HCy). The mixture may be distilled in a
sand-bath, and the product collected in a receiver kept cool by a freezing
mixture. In order to obtain anhydrous hydrocyanic acid, the following pro-
cess is preferable. Introduce the dry cyanide of mercury into a long glass
tube, terminating at one extremity in a receiver immersed in a freezing mix-
ture, and then, from a proper apparatus, pass over it a stream of pure and



COMPOSITION OP HYDROCYANIC ACID. 283

well dried sulphuretted hydrogen, the sulphur of which combines with the
mercury to form sulphide of mercury, while the hydrogen unites to the
cyanogen to form hydrocyanic acid (HgCy + HS = HgS + HCy). The vapor
of the acid may be driven, by the application of a gentle heat, into the cold
receiver, and there condensed. The ordinary process of obtaining this acid,
consists in distilling by a gentle heat 10 parts of finely powdered ferrocyanide
of potassium, with a mixture of 5 parts of sulphuric acid and 14 of water:
the product should be collected in a well cooled receiver. The acid may be
concentrated by digesting it with chloride of calcium. Any Prussian blue
may be separated from it by re-distillation. The hydrocyanic acid thus pro-
cured, should be preserved in a well-stopped phial. In this process, the
cyanide of potassium of the ferrocyanide, is decomposed by the hydrated
sulphuric acid. KCy + HO,S0 3 =KO,S0 3 -f HCy. Cyanide of potassium
may be substituted for the ferrocyanide. Hydrocyanic acid forms no definite
hydrate with water: hence, according to Millon, it may be obtained anhy-
drous from the most diluted solution with as little trouble as absolute alcohol.
He submits the diluted acid to fractional distillation, collecting the distillate
between 120 and 212. After two or three distillations, he passes the
vapor through two Woulfe's bottles, containing dry chloride of calcium, and
condenses it in a receiver, placed in a freezing mixture. The heat of distilla-
tion in the last stage is not allowed to exceed 1*76.

Properties. Anhydrous hydrocyanic acid is a colorless liquid : its vapor
when diffused in air has an odor resembling that of bitter almonds. Its
taste, when diluted with water, is warm and acrid, and it is highly poisonous,
so that the utmost care should be taken to avoid the inhalation of its vapor.
The respiration of a small quantity of this vapor, even in a diluted state,
produces an acrid sensation in the nose and throat, dizziness, sense of weight
in the head, and insensibility. It is irritating to the eyes. The vapor
readily traverses by osmosis, paper, animal membrane, and even caoutchouc.
The anhydrous acid is the most powerful poison known, whether we regard
the smallness of the dose or the rapidity of its operation. Less than a grain
of the acid has destroyed the life of an adult in twenty minutes. The anhy-
drous acid volatilizes so rapidly as to freeze itself, when a drop of it is placed
on a glass plate. Its specific gravity at 64 is 0*696 : and the specific
gravity of its vapor, as experimentally determined by Gay-Lussac, is 0'9476 ;
it boils at 80, arid congeals at 3, or 4 above in its ordinary state ; but
when it is perfectly anhydrous, it remains liquid according to Schultz at
40. It burns with a bright flame. It scarcely affects the blue of litmus.
It is very liable to spontaneous decomposition, especially under the influence
of light, becoming brown, evolving ammonia, and depositing paracyanogen,
changes which are prevented by the presence of minute portions of other
acids, but are accelerated by traces of ammonia or other bases. The pure
anhydrous acid is decomposed spontaneously, whether kept in the light or
dark, whether in open or closed vessels. If highly concentrated, it solidifies
into a brownish-black jelly-like mass. When mixed with strong hydro-
chloric acid, it soon solidifies into a pure crystalline mass of hydrochlorate
o'f ammonia. Millon found that the anhydrous acid forms other compounds,
which are only stable, so long as water is excluded. Moisture destroys
them, and formate of ammonia is produced. The effect of ammonia upon
this liquid is remarkable : a few bubbles of the gas were found to solidify
several ounces of the anhydrous acid. Dilution with water delayed, but did
not prevent this result. The preservative effects of acids, appear to depend
on the neutralization of ammonia or the prevention of its production. When
water is present, the concentrated inorganic acids resolve it into ammonia
and formic acid : 3 atoms of water and 1 of hydrocyanic acid include the



284 DILUTED HYDROCYANIC ACID.

elements of 1 atom of formate of ammonia; 3HO-f H,NC a =H,NC 3 -f XH 3 .
It is resolved by dry chlorine, under the influence of the sun's rays, into
hydrochloric acid and chloride of cyanogen. The changes produced by acids
in the constitution of hydrocyanic acid, show that an excess of hydrochloric
or sulphuric acid employed in its preparation may lead to its decomposition
and contamination with formic acid. As a singular fact connected with this
conversion, Leibig has noticed that when formate of ammonia is transmitted
through a glass tube, heated to dull redness, it is decomposed and is recon-
verted into hydrocyanic acid and water.

C 2 H -f- N = 1 atom of hydrocyanic acid.
3 -j- H 3 = 3 atoms of water

1 atom of formic acid. 1 atom of ammonia.

The easily reducible oxides (of mercury and silver) decompose hydrocyanic
acid, and yield water and a metallic cyanide. When lime or baryta is heated



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