202 Transactions of the American Institute. 



products of combustion are the compounds which are formed. If a 

 body burns in the atmoshphere, it produces an oxide. If it burns in 

 chlorine, it produces a chloride ; as we have produced the chloride of 

 phosphorus, the chloride of sodium, or common salt, and the chloride 

 of antimony in these three jars. 



The Theory of Combustion. 



The subject of combustion attracted, at an early date, the attention 

 of investigators, and various theories were advanced to account for 

 the peculiar phenomena. The phlogistic theory was the first that 

 received credence. Becker, a Prussian, claimed that every com- 

 bustible substance contained phlogiston, and that combustion was 

 due to the escape of the phlogiston ; and hence the ashes were lighter 

 than the substance. Ordinary combustible substances do appear to 

 become lighter, for they pass into gas and disappear. But some of 

 the metals, when they burn, leave behind all the products of combus- 

 tion. Iron burns to a black, and zinc to a white powder. And thus 

 it was found that the remains, which were supposed to be the ele- 

 ments minus the phlogiston, instead of being lighter were heavier ; 

 in explanation of which the theory was advanced that the phlogiston 

 was so light as to buoy up the substance, as hydrogen buoys up a 

 balloon ; the loss of phlogiston leaving the body heavier than before. 



Lavoisier, the great French chemist, who was afterwards guillotined, 

 first announced the correct interpretation of the phenomena of com- 

 bustion. Oxygen had been discovered in the atmosphere by Priestley, 

 and Lavoisier announced that combustion was oxydation ; that the 

 oxygen of the atmosphere produced the phenomena of combustion. 



Still difficulty was met with in explaining the attendant phenomena 

 of heat and light. Some supposed that when bodies burned, they 

 gave up their latent heat and light ; others supposed that their capa- 

 city for heat and light changed. But both these theories were found 

 to be untenable ; for it frequently happened that the product of the 

 combustion had greater capacity for heat than the materials, and con- 

 sequently, upon this theory, combustion of such substances ought to 

 produce cold, instead of heat. 



Sir Humphrey Davy first gave the true theory of the evolution of 

 heat. He attributed the heat resulting from combustion to the vio- 

 lent motion of the atoms of the body, bringing it in connection with 

 that theory now so generally entertained of the correlation of forces 

 by which heat, electricity and chemical action are supposed to be dif- 

 ferent forms of motion; combustion developing heat by motion. 



