A Manual of the Chemistry of the Carbon Compounds

14 TBS CBEMIBTMY OF
metal ahd methyl with methyl, and we obtain ethane or ethyl
hydride:—
20 H8I + Za = Znlg + C8Hfl
By the same reaction ethyl iodide yields butane or butyl hydride:—
2CW + Zn = Znl4 + C4HM
If we replace the chlorine in methyl chloride by cyanogen we
obtain acetonitril C2H3N, a body which does not behave like a compound
of cyanogen and methyl, because it contains the two carbon
atoms linked together exactly in the same manner as they are in ethyl
and acetyl compounds, and we can in fact easily obtain from acetonitril
other ethyl and acetyl compounds.
By these and other similar reactions -we are enabled to prepare from
compounds containing only one atom of carbon in the molecule, others
containing a great number, and thus to build up whole homologous
series.
The existence of such series is particularly characteristic of the
carbon compounds. The ckemkal character of the different series of
togetlicr, whilst the physical properties of each member depend on the
number of carbon atoms it contains. This number may range from
one to thirty or more; and in such a case the lowest members of
the series are often gaseous at the ordinary temperature, the highest
solid, and the intermediate ones liquid (the boiling point rising with
the increase of carbon atoms). They nevertheless all resemble each
other in chemical properties.
If we now, in all the members of such a series, replace hydrogen by
chlorine or another element or compound radical, we obtain other homologous
series, the members of which, as might have been expected,
possess also varying physioal properties, and a very similar chemical
character.
A consequence of this is, that whilst the proportionally limited
number of compounds of other elements allows us to elucidate the
nature and composition of a substance by a few reactions, there exist
only a few carbon compounds which can be recognised by qualitative
analysis. In most cases it is necessary to obtain the compound
to be examined, in a perfectly pure state, to examine its physical properties,
and particularly, when the body is volatile, to determine its
vapour density; and beyond that, not only to study its chemical properties,
but also to find its exact composition by quantitative analysis.
Newly discovered compounds are not the only ones which require
such a complete investigation; in many cases well-known bodies con
only be identified by determining their quantitative composition and
their vapour density.
It is therefore of the greatest importance to be well acquainted
with the methods employed for the ultimate analysis of carbon compounds
and those in use for the determination of vapour density.