298 ATMOSPHERICAL PRESSURE 



The facts that water absorbs air of all kinds, 

 that the quantity of air absorbed is proportional 

 to the pressure and density of the gas, whether 

 it be alone or mixed with other gases, and that 

 certain laws of equilibrium take place, by which 

 water acquires that state in which it is disposed 

 neither to give out nor take in any more gas, 

 have been abundantly proved by Dr. Henry and 

 myself. M. Saussure has shewn the like for 

 other liquids, and for a great number of solid 

 bodies. It may be seen too in my Chemistry, 

 vol. 1st, page 236, that a bladder, which is 

 generally considered as an animal membrane 

 least pervious to air, may be filled with one gas, 

 and being some time exposed to the atmosphere, 

 it will be found to continue full blown as at first, 

 but the contents will be chiefly atmospheric air. 

 Messrs. Allen and Pepys in their ingenious and 

 excellent essays on respiration, have proved that 

 when a Guinea pig, or a pigeon is confined, for 

 an hour, more or less, in a mixture of hydrogen 

 and oxygen gases in proportion as 78 to 22, a 

 large portion of azotic gas is found in the residue 

 and an equal portion of hydrogen disappears. 

 They ascribe this change to effects of respiration; 

 but it appears to me more probably due to the 

 principle we are advocating; namely to the egress 

 of azotic from the whole body and the ingress 

 of hydrogen in lieu of it, in consequence of 



