PHYSICAL PROCESSES IN CELLS. 59 



then a small quantity of water introduced into the tube, the water will 

 almost instantly absorb the gas, which will entirely disappear, and the 

 mercury will rise in the tube, and, with the water, entirely fill it. 



Just as without so also within liquids, gases exert no pressure on 

 each other; so that a number of gases may diffuse at the same time into 

 any given liquid. 



We meet, in this solution of gases in liquids, with laws analogous 

 to those which govern the solution of solids in liquids. Every liquid 

 absorbs at any given temperature a fixed quantity of any given gas, just 

 as a certain quantity of liquid will only dissolve a given quantity of 

 a salt. The volumes which a given liquid at a fixed temperature will 

 absorb of different gases are very different, the most readily-liquefied 

 gases being most readily absorbed. The volume of any gas that may 

 be absorbed by a liquid varies greatly with the temperature. As the 

 temperature increases capability of absorption decreases, until at 100° C. 

 water absorbs no gas at all. The exact opposite holds in the case of 

 solutions. 



The co-efficient of absorption is the volume of gas which a liquid in 

 free communication with a gas can absorb. It varies with every liquid, 

 every gas, and every temperature. According to Bunsen, a unit of 

 volume of water absorbs — 



Gas. Temperature. 



5 oo 



?2()o 



CO, 



Volume. 



1.7967 



.9046 



0.02034 



0.01401 



0.04114 



0.02838 



0.0163 



-« ■ ■ • • J 20° 



O $ °° 



u • ■ ■ ■ 120O 



H 0O 



With every increase of pressure the liquid will absorb uniformlj'- 

 increased amounts of gas. 



Gases absorbed by liquids do not lose their power of diffusion. 

 Hence, if we bring a liquid which contains a gas under a definite tension, 

 e.g., H 2 with C0 2 , in communication with a space containing another 

 gas,H, the C0 2 diffuses out of the H 2 into the space containing the H. 

 C0 2 will continue to leave the water until it exists in equal pressure 

 without and within the liquid ; so, also, H will diffuse into the water until 

 it has a uniform tension without and within the liquid. An absorbed 

 gas is therefore given up when the tension of the gas is less in the space 

 in communication with the liquid than the tension of the gas in the liquid. 

 When two or more gases are mixed together their absorption by a liquid 

 is proportional to the relative volumes of the gases present in the mix- 

 ture, or to the different gaseous tensions. 



In the cell in the animal organism this gaseous interchange occurs 



