50 PHYSICOCHEMICAL BASIS OF PHYSIOLOGICAL PROCESSES 



tances of the curves and the slanting line from the abscissa; i.e., P H , since 

 it is the reciprocal of C H , will be inversely proportional. Lines repre- 

 senting P H may therefore be drawn across the chart, their exact position 

 being most conveniently calculated from the equation P H = 6.10 + log 

 (total C0 2 - 0.0672p) (a modification of . that already given on page 39, 



0.0672p 



and in which p is the partial pressure of C0 2 and 0.0672 the factor by 

 which it is necesary to multiply the tension in order to find the volume 

 per cent of C0 2 in simple solution). As a practical detail in determining 

 the curve it may be mentioned that the blood should be exposed to C(X 

 tensions of 40, 72 and 18 m.m., in the order given (Haggard and Hender- 

 son). If the lowest tension is used first there is danger of laking of the 

 blood with consequent error because of the acid qualities of hemoglobin. 



