400 



be in some measure rotatory as the carbonates may be broken 

 up at greater depths in the earth and converted into sihcates, 

 the absolute independency of the two phases is incontestable. 



We may therefore regard the total alkalinity of the ocean 

 as a quantity that has probably been subject to considerable 

 variations during the geological periods, but it must be ad- 

 mitted on tiie other hand that the variations must go on very 

 slowly, because the altering factors are insignificant compared 

 with the total amount of alkali present in the ocean at any 

 one time. There is at present found about 1.6 x 10"* tons of 

 alkali (reckoned as carbonate of lime) which according to the 

 CHALLENGER-estimate, is. 120000 times the quantity added yearly 

 by all the rivers on the earth. 



I am well aware of the very imperfect character of my 

 remarks upon the alkalinity, but perhaps they may be useful 

 as indicating some points which require clearing up, and the 

 study of which may prove of some hydrographical value. It 

 ought to become possible to draw some conclusions from the 

 alkalinity respecting the former travels of a sample of water. 



Causes ivliicli govern the quantity of carbonic acid. 



1. The influence of the organic life is very easily ac- 

 counted for. Assimilation causes decrease, and dissimilation 

 causes increase in the quantity of carbonic acid. Broadly 

 speaking we may say that the quantity varies inversely as the 

 quantity of oxygen present in the water. This was first ob- 

 served by Knudsen (Ingolf Expedition, Hydrography p. 153) 

 who found that the average quantity of carbonic acid for the 

 samples, possessing a higher oxygen-tension than the atmo- 

 sphere, was 39.8, whereas for the others, showing an oxygen- 

 deficit, it Avas 41.7. Knudsen showed that the variations of the 

 oxygen, as well as the carbonic acid, were due to the plankton 

 and depended upon its vegetable or animal character. 



