OXYGEN ANALYSIS 121 



Fig. 7. The mercury bulb of the analyzer is lifted until mercury 

 runs out through the top of the analyzer and fills the capillary tube 

 of the blood gas diffusion tube. The lower end of the diffusion 

 tube is placed in a beaker of water and the stopper is withdrawn 

 under water. The beaker is raised or lowered until the levels of 

 the fluid inside and outside the tube are the same, and the volume 

 of the air in the tube is read. The stop-cock at the top of the 

 diffusion tube is then turned and a sample of the air within the 

 tube is drawn over into the analyzer and analyzed for oxygen. 



The residual gas from this analysis is nitrogen. As the per- 

 centages of oxygen and nitrogen in atmospheric air are known, 

 it is easy to calculate from the volume of this residual nitrogen the 

 exact amount of oxygen which would have been found by the 

 analysis if no oxygen had been given off by the blood. To do this 



20 93 

 multiply the residual nitrogen by ' , or 0.265. The volume 



I t7 . Lr 



of oxygen thus calculated to have been in the air is subtracted 

 from that found. A correction is then made for the volume of 

 gas which remained in the diffusion tube and connections after 

 the sample was drawn. Corrections are also made for barometric 

 pressure and temperature, for the volume of gas is always expressed 

 as it would be at C. and 760 mm. barometer. The following is 

 an example of this calculation: 



Volume of air in diffusion tube ................... =10.1 c.c. (1) 



Volume taken for analysis ....................... = 9.440 c.c. (2) 



Nitrogen remaining after absorption of oxygen ..... = 7.342 c.c. (3) 



Oxygen absorbed, i.e., (2) - (3) ................... = 2.098 c.c. (4) 



Volume of atmospheric oxygen in volume of gas taken 



20.93 



for analysis, i.e., (3) X ................... = 1.945 c.c. (5) 



79.04 



Oxygen from blood in volume of gas analyzed, 



i.e., (4) -(5) ................................. = 0.153 c.c. (6) 



Total oxygen from blood, i.e., (6) X^T ............ = 0.163 c.c. (7) 



(2) 



Oxygen reduced from barometric pressure 755 and 

 temperature 20 to 760 and 0, i.e., 



760 273 



Volumes per cent oxygen in blood, i.e., (8) XlOO ..... = 14.7 



* Tables for these factors of pressure and temperature will be found in 

 any handbook of chemical constants. 



