THE CHEMISTRY OF COMBUSTION 77 



That is, carbon alone, can produce only carbon. No other 

 kind of matter has ever yet been prepared from it alone. 

 Similarly, hydrogen alone can produce only hydrogen. 

 Substances that have, so far, defied all attempts on the part 

 of man to change them into simpler substances are called 

 CHEMICAL ELEMENTS. About 80 chemical elements are 

 known. The following is a list of the common chemical 

 elements. 



Aluminum Gold Mercury Silicon 



Calcium Hydrogen Nickel Silver 



Carbon Iron Nitrogen Sodium 



Chlorine Iodine Oxygen Sulphur 



Copper Lead Phosphorus Tin 



Fluorine ' Magnesium Potassium Zinc 



85. Energy. If one lifts a weight, WORK is done. In 

 climbing the stairs, work is done. The locomotive works 

 when it pulls the train. The engine at the electric station did 

 work in running the dynamo which supplies the electricity 

 used in lighting (Chap. I, Sec. XI). Electricity may be made 

 to do work by running the electric motor. The engine at the 

 electric station was able to do work because of the heat pro- 

 duced by burning coal. Likewise, any of the fuels studied in 

 the previous chapter may be made to do work by the use of 

 proper machinery. A person is able to do work because of the 

 food eaten. Bodies that are able, by proper means, to do work 

 are said to possess ENERGY. 



DEFINITION. "Energy is work and every other thing which 

 can arise from work and be converted into work" (Ostwald). 



Heat, light, electricity, and the energy of a moving body 

 (KINETIC ENERGY) are different forms of energy. When a body 

 is lifted above the surface of the earth, it possesses energy due to 

 its position Such energy is known as energy of position 

 (POTENTIAL ENERGY). The different forms of energy may be 

 converted into one another. Thus electrical energy may be 

 converted into heat energy or into light energy by means of an 

 electric lamp. Electrical energy, by means of a motor, 



