386 Transactions .—Chemistry. 



with 



which I can attribute this chemical action is hydration. 



Thus the statement hazarded as to the direct hydration of clay-slate by 

 water receives support upon the ground I have just traversed. 



Applying now the facts just elicited in a general manner, it appears 



(].) That in the disintegration of rocks or soils heat is evolved. 



(2.) That the differences in temperature sometimes observed between 

 contiguous strata may be due, wholly or partly, to this cause. 



(3.) That our native anhydrous coals hydrate upon their surfaces when 

 exposed to water or aqueous vapour. 



(4.) That hygroscopic water is chemically-combined water. 



quan 



™ -— — • — -~-w h vv A.HJ 4_LA(~lf r • 



when known, frequently indicate the highest temperature to which 

 they have been subjected. 



(6.) That vegetable matter (leaves, twigs, etc.) generally developes heat 



by hydration; also by friction, when the temperature of the 

 surrounding it is lowered. 



air 



consolidatin 



.« i« g «a ro tnese statements it requires, in the case of (3), gravimetrical 

 experiments to support it, which I shall presently endeavour to obtain, and if 

 they should prove it a correct one, that is, that anhydrous coal can hydrate, 

 and to any notable extent, it will certainly appear that this substance has 



been formed at a somewhat elevated temperature, perhaps approaching to 

 nearly 100° C. e * 



While upon the subject of the formation of coal, I would just like to 

 observe here, that I cannot avoid thinking the effects of pressure in 



, -ilso rocks, are considered much 

 greater than they really have been, and this because it seems that these 

 substances will generally, if not always, be charged with water, oil, or gas, 

 and, if this is so, I conceive the consolidating action of pressure would be very 

 greatly mitigated, and would be in some proportion to its actual volumetrical 

 effect upon the liquid receiving it. I cannot see how particles suspended in, or 

 throughly soaked with a liquid, can be made to approach each other by 

 pressure, except by allowing the liquid to escape, and it does not appear, in 

 the case of rocks, etc., at some depth, that there can be any such way of escape, 

 at least a sufficiently ready one, for the liquids or gases lodged in their pores. 



In reference to the statement (4) that the hygroscopic water of substances 

 reta^ rt „ combined water, this appears certain from what has been 

 n , Prt ,-, lx , , ., Thus, to take an analogous 



I' , ** V e ° f SUver &rms a ie6 ^ "TstaHizaUe chemical 



Ze^ T"T' bUt ' th0 " 8 " "^Wca - «* » can onl y be 



preyed m an atmosphere of ammonia, and if this gas is taken awa aa 



considerations 



