522 



THE RESPIRATORY EXCHANGE 



Furthermore, when several gases are in contact with a liquid, each 

 is dissolved as if it alone were present. All gases exhibit a tendency 

 to expand, and thus exert pressure against the vessels in which 

 they are confined. This property was investigated by Boyle and 

 Mariotte, who independently established the law that the pressure 

 of a gas varies inversely as the volume, provided that the temperature 

 remain constant. As the density of a gas also varies inversely 

 as the volume, the law may be expressed in other words by saying 

 that at the same temperature the density of a gas varies directly as 

 the pressure. This law is not an absolutely rigid one, for gases 

 possess unequal compressibility. Another important law is Henry's 

 Law of the solution of gases in liquids. In a gaseous solution in 

 equilibrium at a given temperature there exists a constant relation 

 between the pressure of the gas dissolved and the pressure of the gas 

 outside the liquid. When the fluid possesses no chemical attraction 

 for the gas, the amount of gas absorbed depends directly upon the 

 pressure. On the other hand, when the liquid possesses a chemical 

 attraction for the gas, the amount of gas absorbed depends upon 

 the pressure, but there is no regular proportion between the volume 

 of the gas absorbed and the pressure. This law is not absolute. 

 As a general rule the solubility of a gas in a liquid diminishes 

 when the temperature is raised. Gases vary in their respective 

 solubilities in different liquids. The coefficient of absorption of a 

 gas is the volume of gas reduced to and 760 mm. which unit 

 volume of the liquid under a pressure of 760 mm. will absorb. The 

 following table is given by Bohr for the coefficient of absorption 

 in water of the gases most important in physiological questions. 



The following example will explain the use of the above data. 

 A hundred cubic centimetres of water are shaken until they are 

 saturated with atmospheric air at 30 ; the amount of gas absorbed 

 is to be calculated as follows. The percentage composition of the 



