SALT WATER. 



611 



as fresh water, which freezes at 32. Salt water requires to be reduced to 

 28 before it freezes. Besides the various constituents mentioned above, 

 sea water has been found to contain boron, bromine, strontia, etc., and even 

 silver, for the copper of ships has been found to be impregnated with that 

 metal. 



If there is so much salt in the sea, it may be asked, why does it not 

 continually become greatly salter by additions. The reason is because tons 

 of fresh water are continually pouring in, and though we can scarcely doubt 

 that the sea is becoming gradually more salt as years pass away, the increase 

 is very slight. On the other hand, evaporation is carrying water into the 

 air and leaving the salt behind it. In seas like the Red Sea, where there is 

 a great deal of evaporation and very little addition of fresh water in com- 



.-"'""' 



Fig. 697. Going out 



parison, the water is extremely salt and bitter. The Baltic has little salt 

 relatively to some parts of the Mediterranean. 



Supposing that, as some allege, there are rocks of salt at the bottom of 

 the sea, we must remember that springs of fresh water frequently bubble up 

 to the surface of the ocean. This is a very curious phenomenon, and has 

 been attested by Humboldt. He states that near Cuba these springs arise 

 with considerable force, and the vessels trading on that coast get supplies of 

 fresh water from these ocean springs. There is, or was, a similar uprising in 

 the Gulf of Spezzia, and fresh water Crustacea inhabit these localities. These 

 occurrences prevent the sea from becoming too salt by evaporation. When 

 salt water becomes tainted it is very offensive much more so than fresh 

 water. If, therefore, the ocean were not continually in movement, it would 

 be very injurious. 



