Molecular State of Carbon

The vaporisation temperature of carbon is exceedingly high, and consequently the vapour density of this element has never been ascertained. Carbon, however, dissolves in molten iron, and it would appear that this fact might furnish a cryoscopic method of ascertaining its molecular weight. But a carbide of iron, and not free carbon, exists in such solution. A hint of the molecular- state of carbon is given by the production of mellitic or benzene-hexa- carboxylic acid, C₆(COOH)₆, from charcoal by oxidising agents. Since phthalic acid is derived from naphthalene by oxidation thus:



it may be presumed that benzene-hexacarboxylic acid -



is derived from a benzene nucleus surrounded by three other benzene rings thus:



It is possible, therefore, that solid carbon is built up of benzene nuclei after this fashion.

Dewar derives the constitution of the carbon molecule from mellitic acid, thus:

→

but Aschan considers that this view does not harmonise with Baeyer's strain theory, and proposes the following constitution for the molecule of carbon in wood charcoal:



Dunroth and Kerkovius, however, bring evidence to show that a molecule of carbon contains C₅-rings as well as benzene rings. Hans Meyer, on the other hand, regards each of the forms of carbon as an aggregation of particles of various sizes, and consequently discounts the value o.f theories as to the structure of the carbon molecule.