HYDROGEN ION CONCENTRATION AND PROTEOLYSIS. 151 



of paralfine for each piece of apparatus were placed. Thus it was possible 

 to obtain a perfect insulation. 



In preparing the different parts of the apparatus extreme care should 

 be exercised to obtain an accurate result. The method for the preparation 

 of the normal element, calomel electrode, gas cell, and also calibration of 

 the biidge wire, ^ etc., is described in detail in Findlay's "Practical Phj's- 



/^p paral u3 



fcmPLOVCD 



in Delerminolion of 



H- Ion Concentration. 



Desckiption of Diagram. 



f\l\a.vvQ. 



Li — Lippmann's capillarimeter. 



L2 — Tungsten lamp. 



A — Accumulator. 



N — Western normal element. 



Si — Switch with quick short circuiting key. 



S2 — Three-way switch. 



S 3 — Two-way switch. 



C — Calomel electrode. 



K — Concentrated KCl cup. 



G — Gas cell. 



B —Bridge. 



P — Thick glass plate. 



ical Chemistry." Every contact should be carefully made, so that accu- 

 rate leadings can be obtained. It is worthy of mention that the diffusion 

 potential between n/10 KCl calomel electrode and the solution to be 

 tested is reduced by interposing the saturated solution of KCl as it is 

 indicated by K on the diagram. For the standardization of the electrode 

 it was first platinized with general precaution; then the hydrogen ion 

 concentration of the mixed solution (7 c. c. of m/15 KH2PO4, 3 c. c. of 

 m/15 Na2 HPO4) 2 was determined at different intervals. After the read- 

 ings became constant there was a difference of 0.0005 volts between the 

 theoretical data and the results obtained. 



' The author is greatly indebted to Professor Thompson, department of physics, Amherst 

 College, for his kind advice. 



' Sorensen's standard solutions. 



