SCIENCE^ADVERTISEMENTS 



WHAT DOES Ph MEAN? 



The symbol Ph is an index of the acidity or basicity — in other words, 

 of the concentration of the hydrogen ions — in a solution. The frequent oc- 

 currence of references to this important quantity in current scientific litera- 

 ture is an index of its growing importance in the chemical and biological 

 sciences. 



Since hydrogen ion concentration of culture media, body fluids and of 

 other solutions has great significance, it is important that its value be accur- 

 ately measureable. 



Color, turbidity, light conditions, or the formation of precipitates should 

 not interfere with the measurement. The result should be actual acidity, 

 unmodified, by a titrating solution. The means for making the measurement 

 should be capable of quick and simple operation . 



THE TYPE K POTENTIOMETER OUTFIT 



Our circular S70 with its supplement 701 gives interesting 

 information about the Type K equipment. These, together 

 with a bibliography of articles on elettromefric hydrogen ion 

 determinations, we shall gladly send you upon request. 



Fully meets these demands. It does more — it has additional features which 

 make it invaluable in the up-to-date research or control laboratory. It 

 measures the entire range of acidity, from Ph = to Ph = 14. The ac- 

 curacy is better than . 01 Ph, and this is limited only by the reproducibiUty 

 of experimental conditions in the medium. 



LEEDS 8c NORTHRUP COMPANY 



ELECTRICALdMEASURING? INSTRUMENTS; 



4901 STENTON AVENUE PHILADELPHIA, PA. 



