MEASUREMENT OF H-ION CONCENTRATION 



443 



Method of expressing H-ion concentration — what is pH? 



The accumulation of free hydrogen-ions present in a given 

 solution, i.e., the H. I. C. of that solution, can be measured to 

 the minutest amount and has been expressed in terms of "nor- 

 mal solutions." The amounts are so minute that they run up 

 to the billionth or trillionth normal, since the acid strength or 

 the hydrogen-ion content of neutral or even alkaline solutions 



TABLE 1 



Comparative values of hydrogen ion concentration expressed in "pH" and "normal" 



solutions 



* By Micronormal is meant one-millionth (1/1,000,000) normal. Symbol /*N. 



is measurable. In order to overcome the unwieldiness of the 

 figures necessary to express the H. I. C. Sorensen suggested 

 the symbol pH to express one-tenth normal beginning on the 

 acid side and going up in negative multiples of one-tenth towards 

 alkalinity. Thus pH 1 equals & acid; pH 2 equals^ Xw = ttoJ 

 pH 3 equals T ^ X & = 1/1000 normal, etc. The lower the pH 

 of a given solution, therefore, the more acid, or the higher its 

 H. I. C. and the higher the pH the less acid, or the lower is its 



