100 STEVENSON— FORMATION OF COAL BEDS. [April i8, 



but proximate analysis showed great differences in volatile con- 

 stituents,' due to difference in combination of the elements. Ignoring 

 the ash, he found the volatile and the coke as follows : 



Calauiodendron 35.3 Well agglomerated. 



Cordaites 42.2 Rather swollen. 



Lepidodendron 347 Well agglomerated. 



Psaronitis 39.5 A little swollen. 



Ptychopteris 39.4 A little swollen. 



Megaphyton 35.5 Well agglomerated. 



He found similar contrasts in modern woods, almost identical in 

 composition, and his conclusion is that plants preserved in coal ap- 

 pear to have different properties though having the same elementary 

 composition, and that external influences were not the only ones 

 affecting the composition and character of the coal. A casual ex- 

 amination of the table might lead one to suppose that the proportion 

 ■of volatile matter had its influence on the tendency to cake, since the 

 well-fused coke was given by coals with about 35 per cent. ; but this 

 may be only a coincidence. Washed "slack " from the Pittsburgh 

 'Coal at Laramie, Pennsylvania, contains, without ignoring the ash, 

 ■as high volatile as even the Cordaites coal of Commentry; it was 

 tested extensively more than a third of a century ago, its coke was 

 strong and with it some extraordinary runs were made in a furnace, 

 100 feet high. All that one can say is that caking may be due to the 

 presence of special hydrocarbons — a sufficiently safe and at the same 

 time a sufficiently broad suggestion. 



to. 



I The Inorganic Content of Coal. 



The ash or incombustible portion of coal varies in quantity and 

 composition not only in different beds but even in the same bed, 

 horizontally as well as vertically. It may be fine, powdery, a con- 

 stituent of the coal itself, or it may be coarse, cindery, coming in 

 great measure from slates or partings. Glance coal is often almost 

 free from ash but the matt coal always has more while the cannels 

 very often have a high proportion. 



In making an effort to compare coals, one is dependent neces- 



