116 Chemistry. [Lecture 28. 



4. Fossil coal charred or coke has much the 

 same qualities of emitting no gross smoke, &c. 

 The reason these fuels improve by being charred 

 is, that before they are so they contain a vast 

 quantity of moisture, which is dissipated in steam 

 or smoke ; these, not being capable of a greater 

 heat than 212, are apt to cool the substances, 

 and sometimes to break the vessels*. 



5. Wood or Coal in their crude state are incon- 

 venient, on account of the smoke or vapour they 

 emit. The smoke, in fact, that arises from all 

 bodies in flame is a vapour not inflamed. Bo- 

 dies that do not flame may heat particular sub- 

 stances more than those that do; yet flaming 

 substances are employed in glass-houses and 

 other works where the greatest heat is wanted- 

 To produce this excessive heat a great quantity 

 of air is necessary ; it is necessary too that the air 

 should be thoroughly mixed and agitated with 

 the flame ; the sooty matter will not otherwise be 

 consumed. The flame of a candle will not pro- 

 duce a violent heat, because the air is not suf- 

 ficiently mixed with it : in a smith's forge, on the 

 contrary, the air is blended with the flame. In 

 heating a furnace, it is of great consequence to 

 throw in but little fuel at once; for if much is 

 thrown in, a great part of the vapour rises in a 



* It is proper to remind our readers that the fumes or 

 vapours of charred coal or coke, are, as well as those of 

 charcoal, highly deleterious ; soon occasioning death, if 

 breathed in an undiluted state. 



