COAL. 381 



The tact that the analyses arc not all of coals from the same scam and 

 locality has not induced the peculiarities in the water contents of the coal, 

 since in both the earlier and the later analyses, inter se, there is no more 

 variation than is everywhere recognized as likely to occur in samples of 

 the same lied taken from sections even within a few feet of each other. 



Other circumstances, such as the length of time a mine has been 

 opened or the depth of the lied beneath the surface, have likewise been 

 without influence, since under both conditions like results have frequently 

 been obtained. 



There is, then, apparently but the one cause — the hygrometric 

 condition of the atmosphere — to which the pronounced variation in the 

 water contents of the above coals can at present lie ascribed. In the drier 

 atmosphere of Denver, under less barometric pressure, they parted with a 

 greater amount of moisture than it is possible to expel under the usual 

 conditions of analysis in the more moist atmosphere and with the higher 

 barometer of the East. But, it is observed, the effect of such varying hygro- 

 scopicitv of coals is not confined to their moisture contents but extends 

 to the estimation of the volatile-combustible matter, and through this to 

 that of the economic value of the coal. Since it is a property of irregu- 

 lar occurrence and one remaining- undetected under precautions hitherto 

 supposed to he ample to obtain accurate results, it should be looked for 

 in all coals and made the subject of special tests, the analyses themselves 

 beini;- conducted according to some standard method. 



The second peculiarity presented in Table II. the relations in the foot- 

 hill coals between the volatile-combustible contents and the fixed carbon, 

 will appear more clearly in the consideration of these constituents in the 

 general discussion that follows. 



GENERAL DISCUSSION OF TABLE II. 



Notwithstanding the peculiarities named in the foregoing pages, from 



the fact that the prairie coals are of the same general horizon (though in 

 some instances of different seams), were laid down under like conditions, 

 and have been subjected to practically the same geological and dynamic 

 conditions, it is probable that throughout they are of approximately the 

 same relative constitution, and a fair comparison maybe instituted between 



