OBSERVATIONS 



RELATIVE TO 



THE MEANS OF INCREASING THE QUANTITIES OF 

 HEAT OBTAINED IN THE COMBUSTION OF FUEL. 



IT is a fact which has been long known, that clays, 

 and several other incombustible substances, when 

 mixed with sea coal in certain proportions, cause the 

 coal to give out more heat in its combustion than it can 

 be made to produce when it is burned pure or unmixed ; 

 but the cause of this increase of heat does not appear 

 to have been yet investigated with that attention which 

 so extraordinary and important a circumstance seems to 

 demand. 



Daily experience teaches us that all bodies those 

 which are incombustible, as well as those which are 

 combustible and actually burning throw off in all 

 directions heat, or rather calorific (heat-making) rays, 

 which generate heat wherever they are stopped or ab- 

 sorbed; but common observation was hardly sufficient 

 to show any perceptible difference between the quanti- 

 ties of calorific rays thrown off by different bodies, when 

 heated to the same temperature or exposed in the 

 same fire, although the quantities so thrown off might 

 be, and probably are, very different. 



It has lately been ascertained, that, when the sides and 

 back of an open chimney fireplace in which coals are 

 burned are composed of firebricks, and heated red-hot, 



