162 



The Realm of Nature 



CHAP. 



know something of its composition and physical properties. 

 The hydrosphere is composed almost entirely (about 96-5 

 per cent) of water, and the total amount of this substance 

 which exists upon the Earth is estimated at about 335 

 million cubic miles or 1,500,000 million million tons. The 

 mass of the hydrosphere is thus about 300 times as great 

 as that of the atmosphere, but its volume is at least 100 

 times less. Pure water is a chemical compound of oxygen 

 and hydrogen united together in the proportion of one-ninth 

 hydrogen and eight-ninths oxygen by mass. Intense heat 

 ( 71), the action of some heated metals, or the passage 

 of an electric current, separate these constituents, giving to 

 water in some rare circumstances the character of an ex- 

 plosive ( 294). The student should read again 66-73. 

 Water, on account of its singularly high specific heat and 

 latent heat, is better fitted than any other fluid for the part 

 it plays in transmitting and regulating energy in Nature. 

 Water is capable of dissolving all natural substances, although 

 some, such as glass or silica, are taken up in minute propor- 

 tions. Natural water is consequently never pure ; however 

 clear it appears, it contains various gases and solids in 

 solution. 



SALTS OF RIVER- WATER 



221. River- water contains salts of many kinds in solution 

 derived from the surface over which it flows. The amount 



