52 GASES OF THE BLOOD. 



the same, but the quantity of gas (weight, density) is directly proportional to the 

 pressure. If the pressure = 0, the weight of the gas absorbed must also = 0. 

 As a necessary result of this, we see that (1.) fluids can be freed of their absorbed 

 gases in a vacuum under an air-pump. 



Coefficient Of absorption means the volume of a gas (at 0C) which is absorbed 

 by a unit of volume of a liquid (at 760 mm. Hg) at a given temperature. The volume 

 of a gas absorbed, and therefore the coefficient of absorption, is quite independent 

 of the pressure, while the weight of the gas is proportional to it. Temperature has 

 an important influence on the coefficient of absorption. With a low temperature, 

 it is greatest; it diminishes as the temperature increases; and at the boiling point 

 it = 0. Hence, it follows that (2.) Absorbed gases may be expelled from fluids 

 simply by causing the fluids to boil. The coefficient of absorption diminishes for 

 different fluids and gases, with increasing temperature, in a special, and by no 

 means uniform, manner, which must be determined empirically for each liquid 

 and gas. Thus the coefficient of absorption for CO 2 in water diminishes with an 

 increasing temperature, while that for H in water remains unchanged between 

 and 20C. 



Diffusion and Absorption of Gases. 



Diffusion Of Gases. Gases which do not enter into chemical combinations with 

 each other, mix with each other in quite a regular proportion. If, e.g., the necks 

 of two flasks be placed in communication by means of a glass or other tube, and if 

 the lower flask contain C0 2 , and the upper one H, the gases mix quite indepen- 

 dently of their different specific gravities, both gases forming in each flask a perfectly 

 uniform mixture. This phenomenon is called the diffusion of gases. If a porous 

 membrane be previously inserted between the gases, the exchange of gases still 

 goes on through the membrane. But (as with endosmosis in fluids) the gases pass 

 with unequal rapidity through the pores, so that at the beginning of the experi- 

 ment a larger amount of gas is found on one side of the membrane than on the 

 other. According to Graham, the rapidity of the diffusion of the gases through 

 the pores is inversely proportional to the square root of their specific gravities. 

 (According to Bun sen, however, this is not quite correct.) 



Different Gases forming a Gaseous Mixture do not Exert Pressure 



Upon One another. Gases, therefore, pass into a space filled with another gas, 

 as they would pass into a vacuum. If the surface of a fluid containing absorbed 

 gases be placed in contact with a very large quantity of another gas, the absorbed 

 gases diffuse into the latter. Hence, absorbed gases can be removed by (3.) 

 passing a stream of another gas through the fluid, or by merely shaking up the fluid 

 with another gas. 



If two or more gases are mixed in a closed space over a fluid, as the different 

 gases existing in a gaseous mixture exert no pressure upon each other, the several 

 gases are absorbed. The weight of each absorbed is proportional to the pressure 

 under which each gas would be, were it the only gas in the space. This pressure 

 is called the partial pressure of a gas (Bunsen). The absorption of gases from their 

 mixtures, therefore, is proportional to the partial pressure. The partial pressure 

 of a gas in a space is at the same time the expression for the tension of the gas 

 absorbed by a fluid. 



The air contains 0'2096 volume of O, and 0'7904 volume N. If 1 volume of 

 the air be placed under a pressure, P, over water, the partial pressure under which 

 O is absorbed = 0'2096 . P ; that for N, = 07904 . P. At 0C., and 760 m.m. 

 pressure, 1 volume of water absorbs '0247 7 volume of air, consisting of 0*00862 

 volume O, and '01 615 volume N. It contains, therefore, 34 per cent. 0, and 

 66 per cent. N. Therefore, water absorbs from the air a mixture of gases containing 

 a larger percentage of than the air itself. 



