MEASUREMENTS WITH ZINC AMALGAMS. 



31 



by a potential measurement, calculating -i- from the equation in which 



n- and T were known. As this was not done, no amalgam derived from No. 3 

 was ever measured against any derived from No. 1. Two independent sets of 

 results were thus secured, which by their agreement established certain con- 

 clusions beyond a reasonable doubt. 



The possibility of polarizing the most dilute amalgams during measure- 

 ments was considered. Momentary currents ranging from 0.001 to 0.00001 

 volt and flowing in alternate directions through a resistance of a thousand 

 ohms can transfer only infinitesimal amounts of zinc. Still, the expected 

 potential was roughly calculated before measurements, to avoid excessive 

 differences at the first contact, and before the final readings were made the 

 cell was shaken to renew the surface of the amalgams. 



The data and calculations for a typical case follow : 



Composition of Amalgam. 



(1) Pipette of amalgam No. 3 = 121.543 



(2) Pipette of amalgam No. 3 = 106.845 



Amalgam No. 3 = 14.698 



(1) Tube -\- mercury = 112.26 



(2) Tube -f- mercury = 69.32 



Weight of mercury = 42.94 



Weight of amalgam No. 3 = 14.70 



Total weight of diluted amalgam = 57.64 

 This diluted amalgam was called No. 4. 



Zinc Dissolved in Ammonia during Mixing. 



Reading. 



Ferrocyanide in burette (1) 46.25 

 Ferrocyanide in burette (2) 46.30 



Ferrocyanide used 0.05 



Needed for end-point 0.01 



Total zinc dissolved 0.04 X 0.003=0.00012 gram. 



14.70 grams of amalgam containing 0.909 per cent of zinc, or 0.013 gram 

 of zinc, were used ; 0.00012 gram zinc is almost exactly 0.1 per cent of total. 

 Therefore, the concentration ratio calculated from the weights of amalgam 

 and mercury must be multiplied by 1.001 to correct for zinc dissolved. 



