60 



DONALD D. VAN SLYKE 



steepest in the middle, when H 2 CO 3 and BHCO 3 are equal (50 per cent 

 of the CO 2 as BHCO 3 ). This fact means that at this point the addition 

 of sufficient acid or alkali to change a given amount of the total CO 2 from 

 BHCO 3 to H 2 CO 3 , or vice versa, causes less shift in pH than at points 

 near either end of the curve, where the ratio BHCO 3 : H 2 CO 3 is much 

 greater or smaller than 1. For example, changing the per cent of CO 2 as 

 BHC0 3 from 50 to 60 alters the pH from 6.10 to 6.26, a change of 0.16; 



3 



80 



8" 60 



40 



g 20 

 u 



Fig 



8 



P H 



Fig. 1. Action of NaHC0 3 :H 2 C0 3 buffer, showing maximum buffer effect at middle 

 of curve when NaHCO 3 :H 2 C0 3 ratio 1. 



while changing the percentage from 85 to 95 raises the pH from 6.85 to 

 7.40, a change of 0.55. It is evident that at pH 7.40, the reaction of 



BHCO, 20 

 normai blood plasma, when the ratio = bicarbonate as a 



When the ratio 



buffer is acting at far from its most efficient point. 

 The phosphates are more efficient at blood pH. 



-p TT~p(~) 



-nrr ~nr? = 1> tne pH i s 6.8, much nearer to the reaction of normal 

 _t>xi 2 -rO 4 



blood than the 6.1 pH of the BHCO 3 : H a CO 3 pair when their ratio 

 is unity. The phosphates are present in so small an amount in plasma 

 that they play a quantitatively negligible role, but they are more important 

 in the cells. Of all the organic and inorganic acids, other than proteins, 

 that might conceivably be used as buffers by the organisms, L. J. Hender- 



