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 iully meets 

 these demanils. It does more — it has additional features which make it in- 

 valuable in the up-to-date research or control laboratory. It measures the 

 entire range of acidity, from Ph = to Ph = 14. The accuracy is better 

 than .01 Ph, and this is limited only by the reproducibility of experimental 

 conditions in the medium. 



Our circular S70 with its supplement 701 gives interesting information 

 about the Type K equipment. These, together with a bibliography of arti- 

 cles on electrometric hydrogen ion determinations, we shall gladly send you 

 upon request. 



LEEDS & NORTHRUP' COMPANY 



[ELECTRICAL MEASURING INSTRUMENTS 



4901 STENTON AVENUE PHILADELPHIA, PA. 



