[ '63 ] 



of the beft Englifli coals diftllled to amount to 73 per cent ; 

 and Dodlor Watfon found the refiduum of Newcaftle coal to 

 amount only to 58 per cent. Thefe refults neceflarily differ 

 according to the degree of heat applied, the duration of the 

 combuftion and the variable admiffion of air. It is plain the 

 bitumen is never totally expelled, at leait not until moft of the 

 carbon is confumed ; but much more of it is expelled by com- 

 buftion than by diftillation. 3 Watfon, p. 27 and 28. 



By Lavoilier's experiments it appears that equal quantities of 

 water under equal furfaces are evaporated, and confequently 

 equal heats produced by*. 



Br 4o3lbs. of coaks 

 6oolbs. of pit coal 

 6oolbs. of charcoal 

 loSglbs. of oak 



^or in meafure <j 



By 17 of coaks 

 10 of pit coal 

 40 of charcoal 

 33 of oak. 



The fame fuperiority of coaks over charcoal has alfo been 

 obferved in Germany in other cafes, though with variations in 

 the refults, plainly arifing from the different degrees of carbonifi- 

 cation. Thus in Silefia it was found that in fmelting of iron ore 

 92lbs. or one meafure of coaks was equal to iSolbs. or 3 mea- 



X 2 fur-es 



• Mem. Stock. 1781. p. 187. 



