132 ESSENTIALS OF CHEMICAL PHYSIOLOGY 



122 mm. pressure of carbonic acid would be different from that 

 contained in water. For instance, alcohol would contain 50 per cent. 

 of the gas. In both fluids the tension of carbonic acid is the same 

 but the quantity of carbonic acid would be as stated, and therefore 

 different. 



The tension of a gas in a liquid, therefore, is the pressure of that 

 gas in an atmosphere of such a composition, that the liquid would 

 neither acquire that gas from the atmosphere nor impart that gas to 

 it, if the liquid and the atmosphere were brought into intimate contact, 

 as by shaking. 



Measurement of Tension in Fluids Aerotonometer, The measure- 

 ment of the tension of gases in fluids is conducted upon the principles 

 of the example given above. The instrument for 

 the purpose is called an aerotonometer. The form 

 used by Loewy consists simply of a closed bottle, 

 into which the blood and the air can be put, and from 

 which they can be withdrawn by suitable means. 

 Through the stopper of the bottle three tubes pass 

 A, B, and c each of which is provided with a piece 

 of rubber tubing and a clip. The tube A is used 

 for introducing or expelling the blood (E). c is 

 used for introducing or expelling the air ; B is con- 

 nected with a rubber bag containing water inside 

 'B AfeotdBonwier. the bottle, while outside a connection can be made 

 with a syringe. A little mercury should be put into 

 the bottle to defibrinate the blood. To determine the carbonic acid 

 tension in blood several bottles should be filled with gases of known 

 composition from gasometers before the experiment. Into each bottle 

 some blood is drawn from the animal. This is done by attaching A to 

 a cannula in one of its vessels, and then, when water is withdrawn 

 from the bag D by the syringe, a corresponding amount of blood enters 

 the aerotonometer. Each bottle is shaken violently for some time. 

 When equilibrium has been established the air can be taken from 

 the air space F by attaching c to an air-analysis apparatus, and forcing 

 water into the bag D from the syringe attached to B. An example may 

 illustrate the result which might be obtained. 



Determination of carbonic acid tension ofblvoil. 



Bottle . .. I II III IV V 



Initial percentage of the gas 5-5 5-0 



Final percentage of gas present . 5'8 5-4 5-1 4-7 



From the above figures it will be seen that the blood has acquired 



