Weather Study 86 1 



The Composition of Air 



Dry air is composed chiefly of oxygen and nitrogen. There are, how- 

 ever, small quantities of carbon dioxide, argon, helium, krepton, neon, 

 hydrogen and xenon, and probably other gases yet to be discovered. 



The approximate proportion, by volume is as follows: Nitrogen 78 

 parts, oxygen 21 parts, argon i part, carbon-dioxide .03 parts, and krepton 

 helium and xenon a trace. Pure dry air does not exist in nature, so there is 

 always present in natural air a variable amount of water vapor, depending 

 upon the temperature and the source of supply. Besides these, which may 

 be termed the permanent constituents of the atmosphere, many other sub- 

 stances are occasionally met with. Lightning produces minute quantities 

 of ammonia, nitrous acid and ozone. Dust comes from the earth, salt from 

 the sea, while innumerable micro-organisms, most of which are harmless, 

 besides the pollen and spores of plants, are frequently found floating in the 

 atmosphere. Recent investigations in atmospheric electricity lead to the 

 conclusion that electric ions are also present, and perform important func- 

 tions, especially with respect to precipitation. 



Oxygen 



Oxygen is one of the most common substances. It exists in the atmos- 

 phere as a transparent, odorless, tasteless gas. It combines with hydrogen 

 to form the water of the oceans, and with various other substances to form 

 much of the solid crust of the earth. Chemically, it is a very active gas, 

 and because of its tendency to unite with other substances to form chemical 

 compounds, it is believed that the volume of oxygen now in the atmosphere, 

 is less than during the early history of the earth. It supports combustion 

 by combining with carbon and other substances, producing light and heat. 

 It combines with some of the organic constituents of the blood, through the 

 function of respiration, which is in itself a slow process of combustion, and 

 thus supports life and maintains the bodily heat. 



Nitrogen 



Nitrogen forms the largest proportion of the atmosphere, but unlike 

 oxygen it is a very inert substance, uniting with no element at ordinary 

 temperatures, and at high temperatures with only a few; and when so 

 united the bonds that hold it are easily broken and the gas set free. For 

 this reason, it is utilized in the manufacture of explosives, such as gun- 

 powder, guncotton, nitroglycerine, dynamite, etc. Its office in the atmos- 

 phere appears to be to give the air greater weight and to dilute the oxygen, 

 for in an atmosphere of pure oxygen a fire once started could not be con- 

 trolled. Although nitrogen does not contribute directly to animal life, in 

 that it is not absorbed and assimilated from the air direct as oxygen is, 

 nevertheless, it is a very important element of food both for animals and 

 plants, and in combination with other substances forms a large proportion 

 of animal and vegetable tissues. 



Carbon Dioxide 



Carbonic acid gas, known chemically as CO 2 is a product of combustion. 

 It results from the burning of fuel and is exhaled by the breathing of ani- 

 mals. It also results from certain chemical reactions. The amount in the 

 atmosphere varies slightly, being somewhat greater at night than by day 



