Researches on the chemistry of coal.—Part III. The extraction of coals by benzene under pressure

In the last paper of this series a new method was described, consisting essentially of a pyridine-amyl alcohol treatment, for extracting and isolating the "resins" present in bituminous coals. It was also shown that they do not usually much exceed 1 per cent. of the coal substance, and that, although doubtless a contributing factor, they are not the chief cause of the coking propensities of such coals. On the contrary, the principal binding power was found to reside in a certain group (provisionally termed "humic" substances) of non-resinous bodies, probably of cellulosic type and origin, whose fusion temperature are below those at which they undergo rapid decomposition. They may amount to as much as 4 per cent. (or even more) of the coal substances in the case of strongly coking coals. Further, it was suggested that, although perhaps not necessarily existing in the free state in the original coal, possibly they may be present in a state of loose combination therein, from which they can be liberated by a moderate degree of heat. The use of pyridine, even when largely diluted with some other solvent, for extracting the coal substances, is admittedly open to criticism on the ground of its possible chemical action; and whilst we have always felt that its replacement by a more neutral solvent would be advantageous in many ways, the difficulty has been to find one which will extract the coal to sufficient degree of completion in a reasonable time. By employing benzene under pressure this difficulty has now been overcome, and the present paper contains an account of our recent experiments in this direction.