Natural Waters. 



75 



ascribed. The remarkable softness of the river Dee, which flows 

 through the granite district of Aberdeenshire, England, has also 

 received special notice. 



The following table represents the average composition of sev- 

 eral well known lake waters of Wisconsin. 



Composition of Wisconsin Lake Water*. 



The softness of the water of Devil 's lake is also to be attributed 

 to the fact that it is located in a sandstone country. 



River water rarely contains large quantities of calcium car- 

 bonate such as occur in some springs, since, owing to the free 

 contact with air it never retains very large quantities of dissolved 

 carbon dioxide. Calcium sulphate in river water is usually ac- 

 companied by sodium chloride and magnesium salts. 



In thickly populated and manufacturing centers the rivers are 

 contaminated with the sewage and trade effluent of the towns 

 and villages, and thus often become foul and bad-smelling. This 

 is to be deplored both on account of the annoyance and injury 

 to health which they cause, and also because of the serious loss 

 to the community of the valuable combined nitrogen and other 

 manurial constituents contained in the sewage. It is estimated 

 that the Mississippi river carries daily to the sea 50 to 100 tons of 

 nitrogen as nitrates. In some cities of America, as well as in 

 Europe, the sewage is pumped directly to nearby lands called 

 "sewage farms." where it is allowed to run at intervals between 



