In his book Principles of ChemistryMendeleev wrote: The molecules of coal, graphite and diamond are very compli-
cated, and carbon atoms exhibit the capability of binding one to
another to form complex molecules in all compounds of carbon.
None of the elements possesses an ability of complicating in such
an extent as does carbon. There is still no basis to deﬁne the poly-
merization degree of the coal, graphite or diamond molecules. One
should believe, however that they contain Cn species, “n” is a large