CHAPTER VIII. 



THE CHEMICAL COMPOSITION OF NATURAL WATERS. 



Our study of the chemical constitution of water, in the 

 last Chapter, led to the conclusion that this liquid consists 

 of two gases, oxygen and hydrogen, united in definite 

 proportions. Such indeed is the composition of absolutely 

 pure water, but such is not the composition of any water 

 known upon the surface of the earth. As a matter of fact, 

 absolutely pure water is never found in the economy of 

 nature. The great stream of water called the Thames is 

 far from being absolutely pure in any part of its course. 

 In the neighbourhood of the metropolis, it is, as every one 

 knows, contaminated with impurities to such an extent as to 

 acquire its proverbial turbidity. The rauddiness, however, 

 is due to the presence of solid particles which are mechani- 

 cally suspended in the water — particles which would in 

 great measure subside if the water were left free from dis- 

 turbing causes, and which could be more or less completely 

 removed by the simple process of filtration. Apart, however, 

 from these mechanically suspended impurities, the Thames 

 water, like the water of every other river, contains certain 

 chemical compounds in a state of solution. Such impurities. 



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