Definition and Introduction. 



If an unlimited quantity of water, in which carbonic acid 

 and other gases are present, is brought into contact with a 

 limited volume of air diffusion will of course take place, but 

 after a sufficiently long time a stable equilibrium will be attained, 

 and the partial pressure of each separate gas in the mixture 

 will then indicate exactly the tension under which this gas is 

 dissolved in the water. In the case of gases, that are only 

 physically absorbed in the water, such as for instance nitrogen, 

 this partial pressure, multiplied by the known coefficient of 

 absorption, will give the exact amount of nitrogen present in 

 the water. On the other hand, the tension can be found 

 indirectly by determining the quantity of nitrogen in a sample 

 of the water. 



In the case of carbonic acid the conditions are quite 

 different. This gas exists in natural waters, and especially in 

 seawater, in very great quantities, but for the most part chemi- 

 cally combined as carbonates and bicarbonates. Nothing can 

 therefore be ascertained about its tension from merely deter- 

 mining its quantity, and, as a matter of fact, up to the present 

 time we know nothing whatever concerning its tension in the 

 ocean or elsewhere in nature. Authors, who have dealt with 

 the carbonic acid in the sea, have , as a rule , ignored the 

 principle of tension or taken it for granted, that the tension 

 in the sea must be equal to the partial pressure of carbonic 

 in the atmosphere. 



