MEASUREMENT OF H-ION CONCENTRATION 



445 



TABLE 2— Continued 



H. I. C. The relationships of pH to normal are given in tables 1 

 and 2. Table 1 gives the comparative values of pH and normal 

 solutions, and micronormal solutions. (The term micronormal 

 meaning a millionth normal, symbol Gu.N.) was coined by the 

 writer to facilitate expressing pH values in terms of normal solu- 

 tion.) Table 2 gives the values of pH and its decimal fractions 

 in terms of normality. These tables were thought desirable 

 because we are in a habit of thinking in terms of normality, and 

 not in terms of pH. 



Methods used to determine the H-ion concentration 



Having decided upon the H-ion concentration as a correct 

 method to determine the acidity of a given solution the question 

 arises how this may be accomplished? Two methods have been 

 described (1) the electrolytic method, and, (2) the colorimetric 

 method. 



The electrolytic method, though the more accurate, is highly 

 technical and requires cumbersome apparatus much beyond the 

 possibilities of the average bacteriological laboratory. 



The colorimetric method depends on the color changes that take 

 place in certain indicators at different acid strength or H-ion 

 concentration. The H-ion concentration has been determined 

 electrolytically for a number of solutions ("buffer solutions") con- 



