The Hydrosphere 



of dissolved solids in river-water may vary from about 2 

 grains in the gallon where a river flows over granite rocks, 

 to more than 50 grains per gallon where the streams traverse 

 a limestone country ; the average salinity of river-water is 

 about 12 grains per gallon or 0-018 parts in 100. The 

 composition of the dissolved solids is different for each 

 river on account of the different rocks traversed, but the 

 accompanying table gives the composition of 100 parts by 

 weight of the dissolved salts of an average sample of river 

 or lake water. The large proportion of carbonates and of 

 silica and the small proportion of common salt (sodium 

 chloride) present are characteristic. 



222. Sea -water. The water of the ocean contains 

 nearly 200 times as much dissolved solids as the water 

 of the land. Sea-water, indeed, is at once recognised by 

 taste as salt, while rivers are pronounced fresh. Although 

 the salinity of sea-water varies from place to place and from 

 time to time within certain narrow limits, the composition 

 of the dissolved solids remains almost the same everywhere. 

 In other words, water collected in any part of the great 

 oceans, and boiled down with suitable precautions so as to 

 leave the solids behind, yields "salt" of almost exactly the 



SALTS OF SEA-WATER 



Sodium Chloride . 77-70 

 Magnesium Chloride 10-80 

 Magnesium Sulphate 

 Calcium Sulphate . 

 Potassium Sulphate . 

 Calcium and Mag- \ 

 nesium Carbonate j 

 Magnesium Bromide 0-20 

 Other Salts , 0-20 



Jglsulphates 

 2-50 J = IO ' 8 



0.30 



Total 100-00 



same composition which is shown in the accompanying 

 table. The only exception which has been proved to this 

 statement is that at great depths there is a slightly greater 



