A Manual of the Chemistry of the Carbon Compounds

TEE CARBON COMPOUNDS. 49
whioh are powerful acids. The constitution of these compounds
may be explained by means of the quantivalence of iron, which is a
tetrad, and forms two series of compounds—ferrou3 compounds, which
contain two atoms of iron as a tetrad group, and feme compounds, in
which two atoms of the metal are combined forming a hexad group,
thus:—
Fe=Cl
Ferrous Chloride || Ferric Chloride
Fe=Cl
If in ferrous chloride each atom of chlorine be replaced by the triad
radical CgNg, the octad radical Fmocyanogcn is obtained, whilst the
hexad radical Fcrricyanogm is formed by iCglTj combining with the
hexad ferric group, thus:—
Hvdiio Fcrrocyauidc Hytlrie Ferricyanide.
C£J. CjNft H^A C3N3H
Fe=Fe Fe~Fe
The formulae given above, and which are those generally used for
their simplicity, represent, as we now see, only half a molecule.
CN
CYANOGEN GAS OB, DICYANOO1N CJNJ = |
CN
Tin's gns, which occurs in small quantities in the gases of iron blast
furnaces, is obtained by the action of heat on the cyanides of mercury,
silver, or gold, and is best prepared by heating dry mercuric cyanide
in a tube or retort of hard glass, and collecting the gas over mercury.
It is colourless, has a pungent smell like prussic acid, and is poisonous.
Cyanogen gas condenses to a liquid under a pressure of about 4
atmospheres, or by exposure to extreme cold under tlio ordinary
pressure; it boils at - 21°, and solidifies at — 34° to a radiated icy
mass. It burns with a beautiful purple flame, forming nitrogen and
carbonic dioxide. Cold water absorbs 4—5 vol. of the gas, and it is
also freely soluble in alcohol These solutions soon assume a brows
colour; after some time a brown powder is deposited, and the aqueous
solution now contains carbon dioxide, ammonia, urea, and a large
quantity of ammonium oxalate :-~
C2Na + 4ELO = C2O4 (NHJ,
When the gas is passed into strong hydrochloric acid, or when a
small quantity of aldehyde is added to its aqueous solution, it takes
up only 2 molecules of water, oxamide being formed:—
ON.. + 2H4O = Co0o(NHa)«
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