FURTHER MEASUREMENTS WITH ZINC AMALGAMS. 



NO. 11. 



Weight of amalgam No. 8, 9.845 

 Weight of mercury, 11.407 



39 



21.252 



C R 21.2^2 , C* 



T~ = ^R7T ; log f = -334i8. 

 c w 9-45 mi 



Potential of Zinc Amalgams. Preliminary Trial of Dilute Solution. 

 n of 1-volt cell. 0.9928 ; t of thermostat = 33.08 C. 



These results seem to prove that Dir should be a positive quantity, even 

 when both the amalgams introduced are extremely dilute. Since, however, 



log - is very nearly equal to log -., the marked difference in values for 



c io c n 



Dir indicates experimental error ; more care must be exercised in this process. 



The only imaginable sources of error seemed to be loss of material in 

 transferring, and failure to mix the mercury and amalgam thoroughly. 



The first difficulty was obviated by the use of a capillary half a millimeter 

 in diameter and somewhat tapered at its very end. The shaking of the cell 

 was a tedious process, since the glass gridiron establishing a connection with 

 the hydrogen generator allowed but little play. After fifteen seconds the 

 observed potential was always equal, within a few units in the fifth place, to 

 the limit approached on long-continued agitation. This limit was recorded 

 as the true reading for the cell. 



As might have been expected, the first reading was too high whenever the 

 mercury was run in on top of the amalgam, and too low in the reverse case. 



A new amalgam, No. 12, very nearly equal in concentration to No. 5, was 

 now prepared. From it No. 13, No. 14, No. 17, and No. 18 were made by 

 dilution in the cell as described above. Various peculiarities in the results 

 were noted, but could not at first be explained. Finally oxidation was de- 

 tected inside pipette No. 12, and careful examination revealed a very small 

 hole, where the upper tube had been sealed off. Experiment showed that 

 two different portions of this amalgam gave a considerable potential against 

 each other. The remainder of No. 12 was thrown away, and all results 

 obtained by its use rejected. 



