no NATURAL SCIENCE. .August, 



the constancy in composition of ocean-water, it is chiefly the quanti- 

 ties of gas in the water which determine the capabiHty of any region 

 of the ocean for supporting life. Owing to the greater solubiUty of 

 oxygen in sea-water as compared with nitrogen, the air contained in 

 normal sea-water, whence fishes obtain their oxygen, is twice as rich 

 in oxygen as the atmospheric air ; but, owing to the slower circulation 

 of the waters, it is much more liable to deterioration ; and quite stagnant 

 water, as under peculiar conditions in some Norwegian fiords, and 

 notably in the Black Sea, may become so impoverished in oxygen 

 as to be quite unable to support animal life of any order higher 

 than bacteria. This deprivation of oxygen is accompanied by a rise 

 in the proportion of carbonic acid derived from the carbon of the 

 animal matter which the lost oxygen has oxidised. 



The whole of the oxygen and nitrogen and a minute fraction of 

 the carbonic acid are derived from the atmosphere, but the major 

 part of the carbonic acid is formed in the water. 



The presence in sea-water of carbonates and loosely combined 

 carbonic acid had been acknowledged long before the outset of the 

 "Challenger" Expedition. In 1777, Bergmann attributed the 

 alkalinity of sea-water to magnesium carbonate ; but the general 

 impression was, that there were only minute traces of carbonates, and 

 that the carbonic acid existed mostly in a state of absorption. It 

 was found, however, that the carbonic acid in sea-water was only com- 

 pletely driven out upon distillation nearly to dryness, if no reagents 

 were added. This was considered to be due to the peculiar affinity of 

 some sea-water salt for carbonic acid, various salts being accredited 

 with this power by different investigators. Tornoe then showed by a 

 long series of combined determinations of alkalinity and carbonic acid 

 that in North Atlantic waters the carbonic acid was present as 

 bicarbonate ; and Dittmar's discovery of the surplus of base over 

 hydrochloric and sulphuric acids confirmed this result and estab- 

 lished it generally, clearing up finally this long vexed question. 



In general, the result of Buchanan's determinations and Ditt- 

 mar's further work in this connection may be stated in brief by 

 saying that "ocean-water from any place or depth contains its 

 surplus base in the form of normal carbonate combined with 

 additional carbonic acid, which latter in the majority of cases falls 

 short of, in a minority of cases comes up to, and very rarely 

 exceeds, that which would produce bicarbonate." Dittmar's final 

 summary as to the distribution of carbonic acid in the ocean is as 

 follows :: — 



ist. Free carbonic acid in sea-waters is the exception. As a 

 rule, the carbonic acid is less than the proportion corresponding to 

 bicarbonate, 



2nd. In surface-waters the proportion of carbonic acid increases 

 when the temperature falls, and vice versa. 



3rd. Within equal ranges of temperature, it seems to be lower in 



