REPOET ON THE COMPOSITION OF OCEAN-WATER. 
139 
VI.— ON THE ABSORBED AIR IN OCEAN-WATER. 
Methods of Investigation. 
The components of the atmosphere, in obedience to the laws of the absorption and 
diffusion of gases, must necessarily pervade the ocean everywhere and to its greatest 
depths ; but their quantitative relations to one another and to the solvent are subject 
to chemical, in addition to purely physical, laws; because the oxygen and carbonic 
acid at least are no sooner dissolved than they enter into chemical relationships, the 
former with the dissolved organic matter, and both with the cell-contents of myriads 
of living organisms which, without them, could have no existence. Yet it is worth 
while to make a guess at what would be the state of matters if ocean-water were 
nothing more than a solution in pure water of that complex mixture of salts which, 
as we have seen, presents such a remarkable constancy in its composition. More highly 
constant still is that of the atmosphere, for it consists everywhere and always of the same 
mixture of (very nearly) 0'21 volume of oxygen, and 0'79 volume of nitrogen per unit- 
volume, contaminated with small variable proportions of vapour of water and carbonic 
acid. The pressure of the atmosphere is subject to variation, but, at the sea-level, it 
never deviates much from that of 760 mm. of mercury. Supposing a certain portion of 
the ocean were separated from the rest, and, after having somehow been deprived of its 
gaseous contents, exposed to the air at a constant temperature of t°. The three gases 
would stream into the water at a steadily diminishing rate until absorptiometric equi- 
librium was established, i.e., a point reached when, for instance, the number of molecules 
of oxygen dissolved in a given small time would be exactly compensated by the same 
number of previously absorbed oxygen-molecules returning into the atmosphere. In the 
case of the carbonic acid, the chemical attraction of the “ free ” base * would make itself 
felt principally at first ; but it is impossible to say, by theory, when this affinity would 
be satisfied, because the “ free ” base includes lime and magnesia, whose bicarbonates (we 
have proved it for the latter, and may assume it for the former), even at ordinary 
temperatures, are liable to dissociation. Assuming equilibrium of dissociation to have 
been established, and the carbonic acid to amount to *0003 of the volume of the atmo- 
sphere, one litre of the water, after complete saturation, would contain — 
At f. Atl5°C. 
Of Oxygen, .... 0’209/Ij c.c. 5 - 83 c.c.t 
Of Nitrogen, .... 0791 /? 2 c.c. 11 '34 c.c.f 
Of purely absorbed Carbonic Acid, about . 0'0003/? 3 c.c. 0'3 c.c. 
* Meaning the base uncombined with muriatic or sulphuric acid, 
t According to my own determinations, regarding which vide infra. 
