ECONOMIC GEOLOGY. , 81 



The above figures show that the differences observable between the 

 various coals as to hardness cannot be ascribed to any essential difference 

 in general composition. The table may be summarised thus* — 



AvEEAGB Composition. 



Fixed carbon. Volatile matter. Hygroscopic ^^ 



water. 



:1 Hard coals 



... 58-0 



34-1 



4-4 



3-5 



3 Medium „ 



... 56-5 



35-2 



5-3 



30 



9 Soft 



... 54-8 



34-9 



5-7 



4-6 



Average of 23 coals ... 56-5 34-6 5-0 3-9 



or exclusive of hygroscopic water — 





Fixed carbon. 



Volatile matter. 



Ash. 



l2 Hard coals 



... 60-3 



35-9 



3-8 



6 Medium „ 



... 62-0 



35-7 



2-3 



9 Soft „ 



.. 58-1 



37-0 



4-9 



Average of 27 coals 



.. 60-0 



36-2 



3-8 



It is probable that in many cases the coals which are soft and 

 crumbly at the outcrop would, wAen freMy raised from a comparatively 

 trifling depth below the surface, be found as serviceable as the hard. But 

 there is reason to fear that the soft coals would deteriorate more or less 

 rapidly by keeping, and that it would be necessary to arrange for their 

 consumption without much delay. The best hard coals, on the contrary, 

 could be stacked for an unlimited time without injury. 



The amount of pyrites in the Assam coals varies considerably. 



Few, if any, of them are free from it, but its injurious 



effect in disintegrating the coal depends to some 



extent on itg mode of occurrence. When segregated into nodules, its 



action is less, both chemically and mechanically, than when more minutely 



disseminated. In some coals the amount is objectionably large, and to 



* No. 17 is not included in this summary. 



( 349 ) 



