200 Transactions of the American Institute. 



nied by an evolution of heat sufficient to produce light, we call it 

 combustion. Ordinary combustion consists of action between the 

 burning body and the oxygen of the atmosphere ; and as the materi- 

 als usually employed by us for heat and light are composed of carbon, 

 or of carbon combined chiefly with hydrogen, ordinary combustion is 

 due generally to the chemical combination of carbon and hydrogen 

 with the oxygen of the air. The heat is due to the chemical action, 

 and the light to the heat. 



We may, therefore, divide bodies into three groups. We call the 

 members of one group combustibles. They are bodies which com- 

 bine with the oxygen of the atmosphere. 2d. The supporters of 

 combustion : oxygen, the atmosphere, on account of the oxygen it 

 contains, certain gases rich in oxygen, etc. ; and 3d. Bodies which 

 are neither combustible nor supporters of combustion. These bodies 

 are, for the most part, already burned ; they are the ashes of the 

 combustibles. Thus lime is the oxide of calcium, or the ashes of 

 calcium already burned. Silica is the oxide of silicon. In fact, all 

 the earthy substances, and the rocks, forming the earth's crust, belong 

 to this group, being the ashes of different metals, or the products of 

 their combustion. 



Oxygen not the only Supporter of Combustion. 



Combustion is not, however, limited to oxydation. Oxygen is not 

 the only element capable of supporting combustion. As an illustra- 

 tion of this, I have here several jars of chlorine, in which we will 

 burn different substances. Chlorine is an elementary gas, characterized 

 by its green color and very disagreeable odor. I drop some antimony 

 into this jar of chlorine, and you see that it takes fire, and there 

 is produced a compound of chlorine and antimony. In the next jar 

 I now show you the union of chlorine and phosphorus. In this third 

 jar, also containing chlorine, I burn a piece of sodium, the metallic 

 base of soda and of common salt. You see it now burns ; the product 

 is chloride of sodium, common salt. 



In addition to oxygen and chlorine, there are many other elements 

 which are. capable of supporting combustion ; as iodine and bromine. 

 Sulphur even will support combustion. If we place a piece of copper 

 in the vapor of sulphur, at a high temperature, it burns and produces 

 a compound of sulphur and copper. Even sodium and mercury unite 

 with sufficient violence to produce the phenomena of combustion, 

 producing heat and light. 



