Structure of High-Rank Coals deduced from Helium Densities

Abstract

Wandless and Macrae¹ were the first to show that a relationship exists between the true density of coals and their hydrogen content. Franklin² extended this work, and on plotting the specific volume (1/d) of a number of coals found that an extrapolation of the straight line drawn through the points, to zero hydrogen content, did not pass through the point for graphite (Fig. 1). For this reason she proposed the hypothesis that the structure of coals is “markedly different from that of graphite”. This is in disagreement with the generally accepted theory that coal molecules are basically fused, polynuclear aromatic structures, that is, islets of small graphitic monolayers which may or may not be associated vertically, and to which various aliphatic groupings are attached. This is suggested in van Krevelen and Chermin's³ plot of density of coals versus carbon content, in which the density of graphite is considered to be “the true limit” of coalification.