OF THALLIUM, INDIUM, AND TIN 3! 



The temperature coefficients of the thallium and indium amalgams 

 exhibit very similar behavior. The concentrated amalgams give a value 

 much lower than 0.00366 (the coefficient of expansion of the unit volume 

 of perfect gas), but as the dilution is increased, the coefficient approaches 

 nearer and nearer to the ideal value. The most dilute indium cell measured 

 gave a value 0.00364, very nearly the theoretical coefficient. This same 

 cell gave a potential only 0.4 per cent different from that demanded by 

 the formula of von Turin ; thus, as the electromotive force approaches 

 the requirement of the gas law, the temperature coefficient does likewise. 



APPLICATION OF THE EQUATION OF CADY. 



The equation of Cady claims that the deviations from the simple equa- 

 tion of von Turin are due to the heat of dilution of the amalgams. 80 On 

 comparing this equation 



with the equation of Helmholtz 



it is apparent that if the former really held true, the last terms of the 

 equations would be identical. This was pointed out by Cady. 



Placing the second members equal to one another and dividing through 

 by T we obtain the expression 



R Cm UTT I \ 



T? In -- = ,~ (4) 



v-r c n dT 



That is to say, the temperature coefficient should depend upon the relation 

 of the concentrations, not upon the electromotive force which they hap- 

 pen to exert. 



This consequence is readily tested by the data in hand. Take for 



example the cell Ci-C2. Here =3.516, and its natural logarithm is 



Cn 



1.2574. Hence the first member of the above equation (4) becomes 



8.316x1.2574 ^.ooo^ 

 1x96,530 



and the second member becomes 



00371347^233887 = 0m000ld&1 

 30.0 



The agreement is so striking that other cases should be studied. 

 ^Journ. phys. Chem., 2, 551 (1898). 



