THE CHEMISTRY OF RESPIRATION 497 



cient of absorption, by which is meant the quantity of a gas physically 

 absorbed or dissolved in 1 c.c. of a liquid at 0° C. and under a pressure 

 of 760 mm. Hg.^ Essentially the same changes result if a watery 

 solution is brought into relation with a mixture of gases, provided, of 

 course, that no chemical attraction arises between the substances 

 dissolved therein and the gases. It need not surprise us, however, 

 to find that the absorption is less now and gradually decreases as the 

 concentration of the solution is increased. 



If a comparison is made between the pressure and the weight of the 

 gas absorbed, i.e., its density or the number of molecules in a certain 

 volume, it will be found that at a constant temperature the weight 

 of the volume absorbed increases and decreases in direct proportion 

 to the increase and decrease in the pressure. To illustrate, the volume 

 of oxygen absorbed by one volume of water at 0° C. and under a pres- 

 sure of 760 mm. Hg amounts to 0.0489 c.c. If the pressure is now 

 doubled, the volume absorbed remains the same, but its weight is 

 doubled. Quite similarly, a lowering of the pressure below 760 mm. 

 Hg does not affect the volume of the gas absorbed, but solely dimin- 

 ishes its weight (Law of Dalton). 



The absorption of the gases by blood or by blood-serum cannot be 

 determined, because oxygen and carbon dioxid form dissociable chem- 

 ical compounds. In fact, even nitrogen has been said by Bohr to 

 possess certain chemical avidities which do not permit it to conform 

 to the ordinary laws of the diffusion of the gases. This, however, 

 is a debatable question. At all events, the fact that the blood con- 

 tains the gases just mentioned in physical solution, as well as in a 

 chemically dissociable state, necessitates a brief discussion of the 

 combinations which they may enter. 



The Extraction of the Gases from the Blood. — Supposing for the 

 moment that we are deahng with a gas held in ordinary physical solu- 

 tion , the following procedure should be followed. The liquid containing 

 the gas is placed in a cylinder and its upper surface is brought into 

 firm contact with a piston, the weight of which is accurately balanced 

 by a counterweight. If this entire apparatus is now placed into the 

 receiver of an air pump, from which the air may be gradually exhausted, 

 bubbles of gas will escape from the liquid and collect in a thin layer 

 between its surface and that of the piston. At this time, therefore, the 

 piston is being balanced by the pressure of the escaping gas and that 

 existing in the receiver of the air-pump. On increasing the pressure 

 in this compartment, a point will be reached at which the gaseous 

 molecules again begin to enter the liquid. Consequently, at this time 

 the impacts of those molecules which are just leaving the Hquid are 

 being counter-balanced, and hence, if the pressure which is required 

 to accomplish this end is noted, we are in possession of a means of 



^Bunsen, Gasometr. Methoden, Braunschweig, 1877; Hempel, Gasanalyt. 

 Methoden, Braunschweig, 1900, and Berthelot, Traite pract. de I'analyse des gaz., 

 Paris, 1906. 

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