83 MALLET: COAL-riELDS OP THE NAGI HILLS. 



it may^ perhaps^ be ascribed the complaints that one occasionally bears 

 from engineers who bave tried tbe coal of its ' burning tbe fire-bars.' 

 But in tbe best coals^ like Nos. 4, 17 and 18, tbe quantity is trifling. 



As tbe assays were necessarily made on samples tbat bad been 

 collected some time previously, tbe percentage of bygroscopic water is 

 probably lower tban would be generally found in fresbly-raised coal. 



Nearly all tbe bard coals caked strongly in tbe crucible, yielding a 



firm, but sometimes tumid, coke. Tbe soft coals 

 Caking properties. 



caked sligbtly, or not at all. But it is known tbat 



some coals lose tbe property o£ caking after tbey bave been exposed to 

 tbe air for a time, and it is quite possible tbat some, at least, of tbose in 

 question would be found to cake wben freshly raised. The coal from 

 Mr. Bruce's heap is one of the few non-caking bard coals, and it has 

 most probably lost tbe property from exposure. The caking character of 

 tbe Assam coal is a most important advantage, in rendering the utiliza- 

 tion of the slack from the mines feasible, by its conversion into coke -, 

 and for steam purposes, a mixture of coal and coke may be found prefer- 

 able to tbe former used alone. 



Compared with Raniganj coal, which is now supplied to tbe 

 .^, T,, . Brahmaputra steamers, ffood Assam coal differs in 



Comparison wxtn Kam- r ^ o 



ganj coal. outward appearance by tbe absence of the markedly 



laminated structure seen in tbe former. The Raniganj coal is " invari- 

 ably composed of laminae of varying thickness, and consisting alternately 

 of a bright jetty black substance, and of a dull lustreless rock. -^ * * 

 On a close examination, the brighter streaks are seen to have a lenticular 

 section. Where thickest, they seldom exceed an inch, and they thin out 

 towards both ends. They appear to be flattened masses of irregular 

 shape in a matrix of a dull black color.^^ * The better Assam coal, on 

 the other band, is very homogeneous, and frequently so devoid of visible 



* Vol. Ill, p, 1S9. 



( 350 ) 



