A DEFINITE H-ION CONCENTRATION 163 



that the sohition with the larger pH is ten times as dilute or ^o 

 as strong as the solution with the lower 2^H. A solution with 

 the reaction pH7 is ten times as strong as a solution of the 

 reaction 2^H8. The former represents a normal solution 

 diluted ten viillion times, the latter a normal solution diluted 

 one hundred million times. 



A difference of Yt ^^ V^ means a difference of 0.9 of a 

 dilution counting the next whole number as the dilution. 

 For example, pH8 represents one one-hundred millionth of 

 normal. 2^H7.9 represents 1 and 0.9 hundred millionths of 

 a normal. 2^H7.8 represents 2 and 0.8 hundred millionths 

 of a normal, etc., manifestly extremely awkAvard figures. 



This pYi method of expressing reactions in such dilute 

 solutions is evidently very convenient. It is recommended 

 by the Society of American Bacteriologists and is rapidly 

 becoming the standard in the United States. 



By titration when used with reference to acidity is meant 

 determining the relative reaction, i. e., the relative H ion 

 concentration of a solution. 



By standardization when used with reference to acidity, 

 is meant adjusting the reaction to some desired degree of 

 acidity or alkalinity, i. e., to some desired H-ion concen- 

 tration. 



Before discussing methods of titration it will be necessary 

 to review in part the theory of solutions, though the student 

 is presumed to be familiar with this. 



Watery solutions may contain any or all of the following 

 classes of substances : strong electrolytes, iveak electrolytes, non- 

 electrolytes. 



Strong electrolytes are so called because their solutions 

 readily conduct the electric current; solutions of weak elec- 

 trolytes conduct electricity slightly and non-electrol^^tes not 

 appreciably. 



The theory for such conduction is that strong electrolytes 

 in solution dissociate, break up into their component parts, 

 and these component parts carry the current. In not too 

 strong solution this dissociation is practically complete. 



Strong electrolytes comprise strong acids, strong bases and 

 salts of these. For example, HCl, H2SO4, NaOH, KOH, 

 Na2S04, KCl, etc. When these substances dissolve in water 



