4O ELECTROCHEMICAL INVESTIGATION OF LIQUID AMALGAMS 



An attempt was made also to determine the heat which the amalgam 

 of concentration c would evolve or absorb on dilution to concentration c 2 

 in the case of one cell. In this trial a 0.9 per cent zinc amalgam on dilu- 

 tion by its own weight of mercury absorbed 52 joules per gram-atom of 

 zinc. 



It seemed very desirable that this thermochemical result should be 

 verified by the application of the equation of Helmholtz: 



through the determination of the temperature coefficient of the electro- 

 motive force. Lack of time prevented this in the earlier work ; accord- 

 ingly the present investigation was undertaken. 



The problem obviously involved simply the extension of the work of 

 Richards and Forbes to two different temperatures, but the execution of 

 the work was less easy than had been expected. Since the value of ATT 

 which would be expected in the case of the above cell is very small, it was 

 found necessary to make AT somewhat large. Measurements were at 

 first made at 30, 15, and o, but the interval of only 15 is too small to 

 allow of an accurate measurement of the temperature coefficient, and so 

 in the final experiments measurements were made at 30 and o C. only. 



Most of this investigation was carried out in identically the same way as 

 the earlier work, and the densities of the amalgams were taken from those 

 results. The methods of purification of the zinc, zinc sulphate, and 

 mercury, the methods of preparing the amalgams, of sealing them in 

 hydrogen, and of introducing them into the cell, and diluting them with 

 mercury, which had been distilled and sealed in hydrogen, were identically 

 the same in every respect. 



The potentiometer used was, however, considerably modified. If in a 



cell of a bivalent metal where 1 = 2, it is desired to distinguish between 



2 



a temperature coefficient of 0.00366 and 0.00367, the potential of the cell 

 at 30 and o must be measured with an error of not more than 0.000002 

 volt. Hence it was clear that a potentiometer more sensitive than that 

 employed by Richards and Forbes would have to be used. Accordingly, 

 much time was spent, with the help of J. Hunt Wilson, in elaborating a 

 suitable potentiometer. As this instrument is described in detail in the 

 foregoing paper, 34 any further account of it is unnecessary here. 



The thermostats, also, were the same as those described there ; they 

 could be relied upon to keep at a temperature constant within 0.01. The 

 thermometers were accurately standardized by means of instruments bear- 

 ing the certificate of the Reichsanstalt. 



4 This monograph, pp. 17 to 20. 



