296 THREE CRUISES OF THE " BLAKE." 



of known strength, and driving off the liberated carbonic acid 

 by boiling gently and collecting it in baryta water of known 

 strength, the amount of acid neutrahzed will give the carbonic 

 acid present as neutral carbonate ; the quantity of baryta neu- 

 tralized will oive the total amount of carbonic acid. 



More than thirty elements are known in solution in ocean- 

 water, but in such minute quantities that no attempt can be 

 made to determine them from small samples. Forchhammer's 

 memoir dealt with surface water only ; but he stated that the 

 percentage of the salts of the sea-water was the same in all 

 parts of the ocean. Dittmar extended this, and proved that in 

 depth also the composition was subject to but one exception : 

 the proportion of lime was larger in very deep water than near 

 the surface. 



Professor Dittmar, in his admirable Report on the samples of 

 sea-water collected by Dr. Buchanan, the chemist of the " Chal- 

 lenger," gives the following analyses as the average composition 

 of ocean-water salts : — 



Chlorine ...... 



Bromine ..... 



Sulphuric acid . . . . . 



Carbonic acid . . . . 



Lime ^ . . . . . . 



Magnesia ..... 



Potash ...... 



Soda ...... 



(Basic oxygen, equivalent to halogens) 



52.292 

 . 0.1884 



6.410 

 . 0.152 



1.676 

 . 6.209 



1.332 

 . 41.234 

 (—12.493) 



Total Salts . . . 100.000 



" Giving the following as the average composition of sea-water : 



Chloride of sodium 77.758 



Chloride of magnesium ..... 10.878 



Sulphate of magnesium .... 4.737 



Sulphate of lime ...... 3.600 



Sulphate of potash . . . . . 2.465 



Bromide of maofnesium ..... 0.217 



Carbonate of lime ..... 0.345 



Total Salts . . . 100.000" 



^ The amount of lime is as 10,000 : 247 in the West India seas, and as 

 10,000 : .371 in the Baltic. 



