president's address. 25 



external physical characters, which determine the class, the 

 quality, and the use to which the various kinds may be applied, 

 so it is also found microscopically, that there are appearances 

 peculiar to the different kinds and qualities of coals. Dr. Hut- 

 ton, of Newcastle, appears to have been the first who clearly 

 pointed out the nature of coal as seen by the microscope. He 

 pointed out more particularly the existence of a peculiar -yellow 

 substance in coals of the cannel kind, and which is seen to form 

 a component part of almost all kinds of coal, w^ith the exception 

 of the anthracites ; and this yellow substance is, in a great 

 measure, connected with the quality of the coal, as a gas- 

 yielding substance. 



"The microscope shows coal to be composed of (1.) a black 

 substance, in molecular or granular particles ; (2.) of the yellow 

 or volatile substance, homogeneous and structureless; and (3.) 

 of earthy mineral matter, mixed with the coaly ingredients. 



" These may be considered as the component parts of all coals, 

 the deficiency or entire absence of any of them distinguishing the 

 quality or nature of the coal. Dr. Hutton also showed that the 

 yellow substance was enclosed in spaces, which he supposed to be 

 closed cavities. But if any given section of cannel coal be care- 

 fully ground down, it will be found that such cavities communi- 

 cate with each other ; in other words, that they form areolar 

 spaces in many instances. The shapes of these spaces are also 

 very various, determined, doubtless, by internal changes taking 

 place in the coaly mass while it is being transformed, and even 

 subsequent to that event. Internal pressure, combined with the 

 pressure from without and other circumstances, which determine 

 stratification and cleavage, have also something to do with the 

 appearances of the coal, as seen in different sections cut in 

 different directions. A coal must be examined by three sections 

 at least : one corresponding to the horizontal face of the bed — 

 another corresponding to a longitudinal vertical section, or in the 

 line of stratification — a third, across the line of stratification. 

 Each of these sections will show differences of appearances, 

 according to the nature of the coal, and the pressure, or other 

 physical influences, to which it has been exposed. 



VOL. III. PT. I. D 



