CHAPTER III 



THE WATERS OF THE OCEAN : SALINITY, GASES 



All natural substances are soluble in water 

 to some extent, be it ever so slight, so that 

 absolutely pure water is never found in nature. 

 Rain dissolves oxygen, nitrogen, carbonic 

 acid, and other gases in its passage through 

 the atmosphere. Carbonic acid increases 

 the solvent power of rain-water, which dis- 

 solves different mineral matters out of the 

 rocks of the continents and islands on which 

 it falls, so that the amount and composition 

 of the dissolved salts in the water of a river 

 vary in accordance with the nature of the rocks 

 of the country through which it flows. Thus 

 the amount of salts in solution may range 

 from 2 grains per gallon in a river flowing 

 over granite rocks to more than 50 grains per 

 gallon in a river traversing limestone rocks, 

 but the average salinity of fiver-water is 

 about 12 grains per gallon, or 0-18 part per 

 thousand, as compared with 35 parts per 

 thousand in average sea-water. 



Scattered over the surface of the continents 

 45 



