ELEMENTS CONTAINED IN SEA-WATEE. 27 



swami3S Into salt marshes with regular outlines. The unequal de- 

 pressions, where the water of the sea evaporated accidentally, are 

 transformed into reservoirs, where the water is conducted from com- 

 partment to compartment, to saturate itself gradually and deposit 

 the pure salt in equal layers. But these are only economical works ; 

 man is confined to regulating the operations of the sea itself.* 



Besides common salt, many substances which are exceptionally 

 found in inland waters and hot springs, form a part of the normal 

 composition of sea-water. The various simple substances which 

 science has been able to discover therein (either directly by the 

 analysis of the liquid, or indirectly by the study of the plants which 

 draw all their nourishment from the ocean) are twenty-eight in 

 number ; but doubtless numerous other simple substances are like- 

 wise contained in sea- water, many of which will not long escape 

 the piercing researches of chemists. 



After oxygen and hydrogen, which constitute the liquid mass itself, 

 the principal elements contained in sea- water are : chlorine, nitro- 

 gen, carbon, bromine, iodine, fluorine, sulphur, phosphorus, silicon, 

 sodium, potassium, boron (?), aluminium, magnesium, calcium, stron- 

 tium, barium. The common fucus and other sea-weeds contain the 

 greater part of these substances, as well as several metals. They have 

 discovered copper, lead, and zinc, in the ashes of Fiiciis vesiculosus ; 

 cobalt, nickel, and manganese in those of the Zostera marina. Iron 

 may be obtained directly by an analysis of sea-water, and finally 

 silver is found in a zoophyte, the Focillopora. Forchhammer has 

 obtained from a branch of this coral about a three millionth of silver, 

 mixed with six times the same quantity of copper, and eight times of 

 lead. A slight proportion of silver is precipitated on the bottoms of 

 ships, in consequence of the magnetic current established between the 

 copper- sheathing and the water of the surrounding sea.f And lastly, 

 arsenic has been found in the boilers of steamers which have been 

 supplied with sea-water.:J: It is true that these various substances 

 only exist in infinitesimal proportions in the water, and it is by in- 

 direct means alone that chemistry succeeds in revealing them ; but 

 the total mass of silver contained in the ocean is estimated at two 

 millions of tons. 



The seas having most probably received from the terrestrial strata, 

 which have been unceasingly worn away by the currents of water, all 



* See below, the section entitled, The Works of Man. 



t Philosophical Transactions, part I. 1865, 



% Bischof, Lehrbuch der chemischen und physihalischen Geologic. 



