Water and its Impurities. 



305 



The average for the temperate zone is 3.05 feet, for 

 tropics 8.5 feet. 



At Sierra Leone there fell on the 22d and 23d of 

 August, 1828, twenty-six inches. At Cayenne in French 

 Guiana 10 inches has heen collected in 10 hours. An 

 acre of water one inch deep is nearly twenty-three thou- 

 sand gallons, and weighs more than a hundred tons. 

 Most of this water sinks into the soil until stopped by 

 impenetrable clay or rock, along which it passes until it 

 emerges and finds some stream in which it passes back to 

 the ocean. 



In the passage of this immense amount of water back 

 to the sea it is liable to become charged with two kinds of 

 impurity, inorganic and organic. I propose to examine 

 briefly the cause of these. The dissolved mineral sub- 

 stances are the greater part of the inorganic. 



In leeching through the mineral crust of the earth it 

 dissolves much of the soluble materials that it meets, and 

 carries them down to lower levels so that they ultimately 

 collect in the sea. An examination of river water shows 

 it to contain solid matters dissolved from the soil. The 

 amount contained of course depends largely on the nature 

 of the soil through which it has passed. Thus we find 

 in the gallon of water which contains 70,000 grains : 



The water of the Loka river contains, 0.05 grains 



Common rain and spring waters,.. .4 or 5 to 60 " 



Albany reservoir water, 4 to 6 " 



Loire river, 9.42 " 



The Garonne at Toulouse, 9.56 " 



Danube at Vienna, 10.15 " 



Rhine at Basle, , 11.97 " 



Rhone at Lyons, 12.88 " 



Thames at Hampton (above London) 15.00 " 



Seine at Paris, 20.00 " 



Scheldt in Belgium, 20.58 M 



These are waters used for supplying cities. 

 The amounts in some other waters are interesting. The 



of solid matter. 



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