This 1894 map oftheSkagerrak shows relatively 

 low salt content compared with that of the 

 Atlantic. High rate of evaporation in the 

 subtropical Atlantic accounts for high 

 salinity. Low evaporation rate in the Baltic, 

 and the many rivers carrying melted snow 

 into the sea, account for lower salinity. 



also realized that the concentration of salt in a particular region 

 depends on the balance between evaporation and rainfall. In one of 

 his experiments he showed that the specific gravity of salt water 

 gave a more accurate measure of the salt content than he could 

 obtain by evaporating sea water to dryness because the final weight 

 of the remaining salt depends on the degree of heat applied during 

 evaporation. 



In 1 819 Alexander Marcet, a retired London doctor, made a 

 remarkable discovery about the constancy "of composition of sea 

 salt. He knew that samples would differ in the proportion of salt 

 to water, but said "all the specimens of sea water which I have 

 examined, however different their strength, contain the same ingre- 

 dients all over the world, these bearing the same proportions to 

 each other, so that they differ only as to the total amount of their 

 saline contents." It was almost a guess because he had only fourteen 

 samples, but his findings were later confirmed by Professor G. 

 Forchammer, who published the results of 150 analyses, and by 

 Professor William Dittmar, who analyzed 77 samples brought home 

 by H.M.S. Challenger. Today we have more accurate means of 

 determining the chemical and physical properties of sea salts, and 

 we know that there are small but significant differences. 



The highest salinity in the oceans is found in the Red Sea (37 to 

 41 parts per thousand) and the Persian Gulf (35 to 40 parts per 

 thousand) ; the lowest in the Baltic Sea (2 to 7 parts per thousand), 

 the Black Sea (i8 parts per thousand), and in fjords and estuaries. 



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182 



