92 A TEXTBOOK OF OCEANOGRAPHY 



An important feature of absorbed air may be noticed hère. 

 In air the proportion, by volume, of oxygen to nitrogen is 

 about 21 to 78, or roughly i to 4, but in water at 0° C. the 

 absorbed gases are présent in the proportion of 34"6 to 618, 

 or roughly i to 2. So that marine organisms breathe in a much 

 higher proportion of oxygen than land animais. On the other 

 hand, a land animal which has inhaled 1,000 ce. of air will 

 hâve passed into its lungs 210 ce. of oxygen, but a fish which 

 has passed a similar quantity oî water over its gill.s will thereby 

 hâve had access to 10 ce only of oxygen. Anyone who has 

 kept fish in aquaria will hâve been struck by the small quantity 

 of oxygen required to sustain life. As a rule solutions of sait 

 hâve a smaller coefificient of absorption than pure water, 

 although in certain solutions the atmospheric gases may enter 

 into chemical combination with the salts, and so a higher power 

 of absorption is exhibited. This is especially the case with 

 Carbon dioxide. 



A great deal of work on the détermination of the atmo- 

 spheric gases dissolved in sea-water has recently been done, 

 under the auspices of the International Council for the 

 Investigation of the Sea, by Jacobsen and Fox. As a rule 

 two samples of water are required, one for an estimation of 

 oxygen and nitrogen, the other for the carbonic acid. The 

 estimation of thèse gases is extremely technical, and for the 

 détails the original papers published by the Council should 

 be consulted. 



Dissolved oxygen and nitrogen are met with in sea-water, 

 not only in the surface layers, but also in great depths. For 

 nitrogen the proportion absorbed by the deeper layers is what 

 one would calculate for a surface water of similar density and 

 température, and from this it is concluded that the bottom 

 layers of water were once in contact with atmospheric air at 

 the surface. For oxygen the calculated and observed results 

 in deep water differ considerably, there being always a déficit 

 in the observed results. This is doubtless due to the fact that 

 the oceanic animais hâve utilised a part of the oxygen for 



