CHAPTER IV. 

 NATURAL WATERS, 



Pure water — fe., the substance hydrogen oxide, H^O — practi- 

 cally never occurs in nature. Owing to its remarkable solvent 

 properties, water dissolves smaller or larger quantities of every 

 substance with which it comes in contact. 



The purest form of natural water is rain, although, as 

 shown by the analysis on p. 30, rain-water is never pure, but 

 contains varying quantities of dissolved matter. In addition 

 to those mentioned in the Table, rain-water contains dissolved 

 gases. When it reaches the earth the water at once com- 

 mences to dissolve the substances upon which it falls. In dis- 

 tricts where the surface is composed of hard, igneous rocks the 

 quantity dissolved is small, while on limestone or chalk large 

 amounts of calcium carbonate particularly go into solution. 

 The water which drains away from a soil amounts in England 

 to about half the annual rainfall. Part of it finds its way 

 into the nearest watercourse, thence to a stream or river, and 

 finally to the sea. Another portion sinks into the earth until 

 stopped by some impervious layer of rock — e.y., shale— when 

 it accumulates, and eventually finds an outlet at some lower 

 level in the form of a spring. 



The chief forms of natural waters may be classed as follows . 



1. Rain water, 3. River water, 



2. Spring water. 4. Sea water. 



1. Rain Water. — The composition and character of this 

 has already been described in chap. ii. The acidity of the 



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