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The National Geographic Magazine 



FILTERING OUT THE SALT 



The salted earth is unloaded into two wooden tanks, in the bottom of which a layer of 

 straw and sand has been placed. Salt water is poured over the earth and filters through the 

 straw and sand. The saturated water is collected into another tank buried under those which 

 are in sight. To ascertain the density of the solution a new laid egg is introduced into it. 

 The operation is concluded when the primitive areometer is nearly but not completely sub- 

 merged. 



Solid <uJt. f«»^. 



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 DIAGRAM TO EXPLAIN THE FILTER TANKS 



