206 ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. 



metallic and other elements of the earth, forms also, in union with 

 hydrogen, the great body of water which covers three-fourths of the 

 terrestrial surface. Water consists of two volumes of hydrogen and 

 one volume of oxygen chemically combined. Stated by weight, out of 

 nine parts of water eight are oxygen. But water, as we know it, always 

 contains other matter, and chiefly atmospheric air, which is dissolved 

 in it, and to a considerable extent changes its character. For the serv- 

 ice of man, water, deprived of air, would have lost several important 

 characteristics. Oxygen is dissolved in water to the extent of 2.99 

 volumes to 100 of water at 15° C, an amount sufficient to support the 

 existence of fishes and hosts of other aquatic creatures, aud to oxidize 

 and render innocuous some of the common impurities which result from 

 animal and vegetable processes and decay. Probably its power when 

 dissolved in the liquid is greater than in the atmosphere, and it must 

 be compressed into a smaller space. Fresh charcoal absorbs eighteen 

 times its volume of oxygen, and a much larger bulk of organic vapors, 

 especially ammonia; in this condensed state the oxygen acts so power- 

 fully as to unite with hydrogen to form water vapor, and with sulphur 

 to form sulphur dioxide. We may thus assume that water, as we use it 

 and drink it, has important effects upon the body which would not take 

 place if robbed of its contained oxygen. As an instance of the value 

 of the air contained in water for many domestic purposes, its assistance 

 in the making of tea may be mentioned; if the air be allowed to boil out 

 of the water the beverage is spoiled. Recent observation, however, 

 shows that oxygen is not altogether removed from good water by the 

 process of boiling. 1 



Oxygen has a very strong chemical attraction for the elements; only 

 one is known with which it does not combine. Hence, "to burn" in 

 common language means combination with oxygen, and most sub- 

 stances in the crust of the earth are already burnt, or combined with 

 oxygen. In its ordinary form it has no color, taste, or smell, according 

 to most observers, but recently a faint blue color has been detected as 

 belonging to it, when seen in sufficient quantity. It has a small 

 refracting influence on light, and exhibits a magnetic property, espe- 

 cially strong in the liquid form, to which it has recently been driven by 

 intense cold and pressure. The degree of cold required was — 140° C. 

 under a pressure of 320 atmospheres. 



The 2>roportion, by weight, of oxygen in the air has been determined 

 by Leduc as 23.58 per cent. 2 



The volume of oxygen in the air in different localities and conditions 

 has been tested by various observers. On the western seashore of 

 Scotland the percentage was found to be 20.991; on the tops of hills, 

 20.98; in a sitting room (close)', 20.89; at the backs of houses, 20.70; 

 at the bottom of shafts in mines, 20.44. 



1 See Comptes Rendus, 1890. M. Muller. 



2 Coiuptes Reudus, 1890. A. Leduc. 



