24 INGREDIENTS IN SEA-WATER, 



a change in the constitution of the waters, as well as in 

 the climate of the globe. 



Several different salts are held in solution in sea- 

 water. The chief ingredient is common table salt, or 

 chloride of sodium. Besides this, which amounts to a 

 very large proportion of the whole, sulphates and 

 carbonates of magnesia and lime, with a little potash 

 and some free carbonic acid, and minute quantities of 

 other minerals, have been detected. Two curious ele- 

 mentary substances, Iodine and Bromine, occur in sea- 

 water, but in such " homoeopathic " quantity as to be 

 rarely tangible, unless a very large body of water be 

 experimented upon. Iodine was first discovered, at a 

 soap manufactory, in an alkaline solution or ley, which 

 had been prepared from seaweed ashes ; and it is readily 

 procurable from certain seaweeds and marine mollusks 

 which, no doubt, secrete it gradually from the water 

 that entei-s their tissues. Bromine, first found in the 

 bittern or mother-water of a salt manufactory, has like- 

 wise been detected in marine plants, but is more abun- 

 dant in some salt-springs, particularly in those of Ger- 

 many. The relative proportions of the various saline 

 substances, though generally the same over wide spaces, 

 vary now and then from local circumstances. Thus 

 the waters of the British Channel, which flow upon a 

 bed of chalk, have been found to contain nine times as 

 much lime as those of the Mediterranean. The sea in 

 the neighbourhood of coral reefs or islands usually holds 

 much lime in solution, and deposits it on tidal rocks, 

 and on the seaweeds that cover them, and incrusts the 

 grains of sand and gravel that compose the beaches. 



