[ i67 ] 



Mr. Lavoisier has alfo given the cubic meafures of thefe 

 combuftibles, and the times in which each of them produced the 

 fame efFedl. For the fatisfadlion of the curious I fhall exprefs 

 the whole in the following table : 



Hence we fee that if coal produces a certain quantity of 

 heat in a given time, coaks in much fmaller quantity will pro- 

 duce the fame effedl in little more than half that time, an equal 

 weight of charcoal in one-fourth of that time, and oak in nearly 

 double the weight of the coal in about one-fifth of that time. 



The beft coal for common ufes feems to be that which con- 

 tains no pyritous, earthy or flony matter, and in which the 

 carbonaceous is to the bituminous part in the proportion of 5 

 to 4, or 6 to 4,5. An equal mixture of maltha and afphalt is pre- 

 ferable to either fingly. 



