CHAPTER XVIII 
THE SALT DEPOSITS! 
Composition oF SeA-WaTer—The characteristic feature of 
sea-water is its saltness. The analyses by Dittmar of the 
many samples of sea-water collected by H.M.S. “ Challenger 
(1873-6) show the following composition :— 
Sodium chloride 
Magnesium chloride 
Magnesium sulphate 
Calcium sulphate 
Potassium sulphate . 
Calcium carbonate . 
Magnesium bromide 
Per cent. 
77758 
10-878 
4737 
3-600 
2-465 
0345 
0-217 
{00-000 
The variations from this composition are slight except 
near the mouths of great rivers and in enclosed seas, i.e. a 
sea with only one outlet, such as the Mediterranean and the 
Baltic. If an arm of the sea be cut off from the ocean and 
its water evaporated, the salts are deposited in the order of 
their insolubility. When 37 per cent. of the water has been 
removed the calcium sulphate is deposited ; when 93 per 
cent. has gone common salt (sodium chloride) and sodium sul- 
phate are precipitated ; the magnesium chloride, potassium 
chloride, and bromine are left in the brine which, from its 
taste, is known as bittern. The chlorides in the bittern are 
50 soluble that they are not deposited unless all the water 
!¢ The Geology of Potash,” with some account of the German salt 
fields has Deen given by the author, 77, G.S. Glasgow, xvi, 1916, pp 
12-33, pl. I. 
230)