3{j 



(for example, the simple solution containing C.CCSm 

 Cu(NC3)2 and the combination solution containing C.CCSm 

 Cu(NC3)2 and C.C5m Ca(NC3 )2) were placed in the two arms 

 of a U-tube separated below by a saturated solution 

 of ammonium nitrate. Into each arm of the U-tube was 

 introduced a copper electrode and these were connected 

 with the potentiometer. The potentiometer was so calib- 

 rated that the difference in voltage between the two cop- 

 per solutions might be read directly on the- instrument. 

 The copper electrodes were freshly plated and calibrated, 

 for subsequent correction of the readings, with reference 

 to any difference in potential which might exist between 

 them when both are placed in the simple Cu(NC3)2 

 solution. 



The difference in concentration of copper ions 

 in the two solutions thus compared was calculated from 

 the observed difference in electrical potential by the 

 following formula: 



C_ 



Y - C.C591 log 3^r Ci 



in which Y is the observed 3. l.!. F. in volts, C and C^ 

 are the concentrations, respectively , of the copper 

 ions in the two solutions and the quantity C.0C91 is a 

 constant. 



In the tests with which we are at present concerned 



