28 



ELECTROCHEMICAL INVESTIGATION OF LIQUID AMALGAMS 



Examination of these results shows that the observed potentials of the 

 amalgam cells of tin, like those of all the other metals thus far studied, 

 approach the theoretical requirements more and more closely as the dilu- 

 tion is increased. The results are depicted graphically by the curve in 

 fig. 8. It should be noted that the sign of curvature is exactly the reverse 

 of that of the otherwise similar curves obtained with cadmium, thallium, 

 and indium amalgams, since tin amalgams deviate in the opposite direction 

 from theory. In this respect tin is similar to zinc. 



-I 



logZ 



log 16 log3Z log 64 



Fig. 8. The Deviations of the Electromotive Force of Tin Amalgams. 



r> *j* 



Deviations from the expression ir = - - - i n are plotted in millivolts as 



1r C% 



ordinates, the logarithms of the concentration ratios as abscissae. 

 The most concentrated amalgam contained 0.66 per cent by weight 

 of tin and 99.34 per cent by weight of mercury. A horizontal 

 line on the diagram would indicate complete fulfilment of the 

 concentration law. This curve is for 30. The most concentrated 

 amalgam separates solid at o. 



In the case of the tin amalgam cells complete exclusion of oxygen is 

 necessary, not only on account of the amalgams, but also in order to 

 insure the stability of the electrolyte, since stannous chloride when exposed 

 to the air quickly becomes basic according to the equation : 



When the solution is in contact with tin amalgam in the air this reaction 

 proceeds very rapidly, perhaps because the stannic chloride is reduced by 

 the amalgam. The formation of stannic chloride would be expected to 

 lower the potential, and the constancy observed in the values of the various 

 cells proves the complete elimination of any such disturbing effect. 



