58 SCIENCE OF COMMON THINGS. 



Salt lakes. Effect of salt in the ocean. Mineral springs. 



are continually changing and discharging themselvea 

 into the sea ; therefore the salt does not accumulate, 



345 Is every lake into which rivers flow, and from which there ts no 

 outlet except by evaporation, a salt lake f 



It is j and it is curious to observe that this condition 

 disappears when an artificial outlet is provided for such 

 waters. 



Such lakes are the Dead Sea, the Caspian, the Sea of Aral, and the 

 Great Salt Lake of Utah, the saltness of all of which exceeds that of the 

 ocean. 



346 What good purposes does the presence of so much salt in the ocean 

 subserve f 



It depresses the freezing point of the water many de- 

 grees, thereby diminishing the dangerous facility with 

 which fields of ice are formed in the polar regions ; it 

 also aids in preventing the corruption of the water by 

 the accumulation of animal and vegetable remains. 



347 What are the substances extracted from the earth which we find 

 in sea water ? 



The most abundant substance is common salt ; next, 

 certain combinations of magnesia : then salts of lime, 

 with small proportions of potash, iron, iodine, and bro- 

 mine. 



348 Are these substances found in most springs f 



With the exception of iodine and bromine, they may 

 be found in small quantities in almost all springs and 

 rivers. 



349 Are those substances which we caU impurities in water of any ser- 

 vice to animal or vegetable systems f 



They give to water its freshness and sparkling pro- 

 perties j pure distilled water is very disagreeable to 

 drink ; these substances are also generally beneficial to 

 the systems of plants and animals, and are absorbed by 

 them with the water. 



350 Does water form part of the composition of most bodies f 



It enters directly into the composition of nearly all 

 crystallizdble bodies and most organic compounds. 



351 If the waters of the ocean were not agitated by winds, currents, 

 and tides, what would be the effect f 



