G SIXTH RKPORT — 1836. 



external water, and would receive any air, whicli upon the re- 

 moval of the pressure might escape from the body of the vessel. 



This instrument has been exhibited at the Mechanical Section, 



but I am loth to occupy more space in its description, until it 



has been put to the test of experiment in the open sea *. 



Gases pre- The gaseous contents of sea-water, which wilii an apparatus 



sent in Sea- of this description may be collected and examined, have not as 



water. y^^ received the attention they appear to deserve. 



I\I. Arago remarks, that oxygen predominates over azote in 

 the surface water both of the sea and of rivers f, and likewise in 

 that of the Mediterranean even at a depth of 1000 metres ;]:. 

 This latter observation, however, is rendered doubtful by the 

 imperfection of the means hitherto employed for drawing up 

 water from the sea; and supposing it correct, still, as M. Arago 

 remarks, we are left in the dark, as to whether the same law holds 

 good at greater depths. 



The determination of this point, hov/evcr, is of the more im- 

 portance, inasmuch as some observers have supposed the bub- 

 bles of gas, which occasionally rise up througli the sea in the 

 vicinity of volcanos, as, for example, off the coast of Sicily, to 

 have been disengaged from sea-vvater ; now these bubbles, un- 

 like what would have been the case, had they been derived from 

 the air existing in tlie surface-water, were found to contain a 

 predominance of nitrogen gas§. The pressure exercised upon 

 sea-water at great depths would also enable it to hold in solution 

 much larger quantities of air, tb.e presence of which, supposing 

 it to consist in part of carbonic acid, might cause the waters to 

 dissolve a greater amount of carbonate of lime, and thus afford 

 a more abundant supply of that ingredient to the numerous 

 moUuscfe, that are building up extensive calcareous formations 

 within the ocean. 



Water of Inland seas and lakes may be divided into those vt'hich pos- 



Lakes. scss an outlet, and those which are destitute of one. 



The water of the former commoidy corresponds with that of 

 the rivers which flow into them; that of the latter contains in 

 general the same ingredients as sea- water, but in a state of much 

 greater concentration. 



* This apparatus lias since been tried off Margate in water of 50 feet in 

 depth, and appeared to answer perfectly. 



t The most recent experiments en this subject are those of Dr. Thomson, 

 (Records of General Science for Sept. 1836,) who found that the air contained 

 in Clyde water consisted of 70-9 azote, 29' 1 oxygen, and that when a 

 mixture of the two gases v/as placed over water, the oxygen was absorbed 

 much more readily and in larger quantities than the azote. 



I Annuaire, 1836. 



'5' Philosophical IVa/isaclions, 1834. 



