80 



DONALD D. VAN SLYKE 



TABLE I 

 PERCENTAGE OF CO 2 IN THE FORM OF BICARBONATE AT DIFFERENT pH LEVELS 



the values of R calculated from the equation log R = pH - - pKj Table 

 I is computed. 



Titrimetric Determination of Plasma, or Serum Bicarbonate. The 

 plasma or serum (1 c.c.) is acidified with 1 c.c. of N/20 HC1, and is 

 completely freed from CO 2 by whirling the acidified mixture about the 

 inner wall of a small round flask for 1 or 2 minutes. The mixture is then 

 titrated back to the initial pH of the plasma with N/100 NaOH, phenol 

 red being used as indicator. Since at the same pH every buffer acid, 

 other than the escaped carbonic, binds the same amount of alkali as 

 before the titration, the effect of the titration is merely to change all 

 the BHCO 3 to BC1, and the HC1 utilized is equivalent to the BHCO 3 

 (Van Slyke, Stillman, and Cullen, 1919; Stillman(6), 1919; Van Slyke 

 (h), 1921). All the solutions used are made up in 0.9 per cent NaCl 

 solution instead of in water. At the end of the titration the volume is 

 brought up to 15 c.c. by addition of 0.9 per cent NaCl solution. 



The end point is ascertained by comparing the color of the titrated 

 solution with that of a control tube prepared by mixing under paraffin 

 oil 1 c.c. of plasma with 14 c.c. of 0.9 per cent Nad solution. 



Electrometric Determination of the Plasma pH. The electrometric 

 determination is the standard on which others are based. For a description 

 of both principle and technique, which cannot be taken up here, see W. M. 

 Clark's recent work (1920). As shown by Parsons (1917) the pH actu- 

 ally determined is that of the plasma, whether the corpuscles are suspended 

 in it or are absent. All blood pH figures which are at present available 

 therefore represent the plasma pH. This is true even when the pH is 

 calculated from the BHCO 3 : H 2 CO 3 ratio, since the constant of Hassel- 

 balch's equation is based on electrometric determinations. The pll of the 

 cell contents is presumably a little lower (Michaelis and Davidoff, 1912). 

 That it parallels that of the plasma, however, is shown by the fact that 

 change in the BHCO 3 : H 2 CO 3 ratio of the cells parallels that of the 

 plasma (Joffe and Poulton, 1920; Fridericia(6), 1920). 



