[ i64 ] 



fures of charcoal *. Elfewhere it was remarked that one mea- 

 fure of coaks were equivalent to 5 of charcoal and 3 of pit 

 coal |. Doubtlefs according to the quality of this laft. 



The caufes of thefe differences deferve attention, as the con- 

 trary might be prefumed. For in the firft place I have ftated 

 that the carbonic part of pit coal is esadlly the fame as common 

 charcoal, and therefore when equal weights of both are em- 

 ployed it fliould be expedled that the calorific effedts of both 

 fliould coincide. In the next place it is known that pit coal 

 and woods containing a large proportion of oil muft contain 

 a large proportion of inflammable air, and this in combuftion 

 gives out more heat than an equal weight of mere carbon 

 in the proportion of 3 to i f. Therefore it fhould feem that a 

 fmall quantity of wood fhould produce the fame calorific effedl 

 as a larger of charcoal. 



To remove thefe difficulties I fliall lay down two pofitions : 

 I fl, That the quantity of heat given out by carbon is to that 

 given out by an equal weight of inflammable air (or hydrogen 

 as it is now called) as i to 3. 



2dly, That to communicate equal quantities of heat, in the 



cafe now before us, atmofphcric air muft have taken up either 



equal quantities of mere carbon or a quantity of inflammable 



air equal to onc'tliird of the deficiency. 



Now 



• I Bergm. Jour. 1790. p 320. J i Bergm. Jour. 1792. p. 60. 



f I Chy. Lavois. p. 104. 



