68 



A TEXTBOOK OF OCEANOGRAPHY 



The mean quantity is approximately 35*976 grams in 1,000 

 grams of sea- water that is, 3j per cent. Sea- water has the 

 properties of a dilute solution of salts that is to say, as com- 

 pared with fresh water it has a lower freezing-point and vapour 

 tension, a higher osmotic pressure, electric conductivity, 

 viscosity, and surface tension. 



Sea-water is also an important medium for the development 

 of organisms, both animals and plants ; the latter can in the 

 presence of sunlight build up organic from inorganic matter, 

 thus playin'g an important part in the circulation of matter in 

 the sea. 



The Salts in Sea-Water. 



Of the 80 elements known to modern chemistry, 32 have 

 been identified in sea-water. Probably all are present, the 

 majority in such small quantities as to elude identification. Of 

 the 32, the following 7 are the most important : Chlorine, 

 bromine, sulphur, potassium, sodium, calcium, and mag- 

 nesium. 



Analyses of sea-water give the following results. Those 

 of Thorpe were from the Irish Sea, where the salinity is less 

 than in the open ocean. 



SALTS IN 1,000 GRAMS SEA-WATER. 



Dittmar's and Forchhammer's analyses were made, the 

 former from Challenger material collected from various parts 

 of the world, the latter from water for the most part from mid- 



