OF THALLIUM, INDIUM, AND TIN 7 



as seems to have been the custom of previous workers in this field. 

 Richards and Forbes have shown the necessity of applying a correction 

 for the difference in density of the two amalgams being compared. For 

 example, let w be the weight of an amalgam of concentration c t diluted 

 with w Hg grams mercury to form a new amalgam c 2 . Now, if Z) x and D 2 

 are the densities of the amalgams, we have 



w l 



C\___V* ___ Dt _ Z^l + 



c 2 v l ~ w w v t 



D, 



Careful determinations were made of the densities of the several amal- 

 gams at various concentrations ; and corresponding corrections were 

 applied to the calculated values of the concentration ratio. These determi- 

 nations will be considered later in their proper place. The densities were 

 all measured at 20 ; their relative values undoubtedly change slightly 

 with the temperature, but not enough to affect appreciably the calculation 

 in question. 



In calculating the thermochemical results, one 18 calorie was taken as 

 equal to 4.181 joules.* 1 



A number of typical cadmium standard cells, containing crystals of 

 cadmium sulphate, prepared from different pure materials at different 

 times, were used as the standard of electromotive force. As these all 

 agreed within the tenth of a millivolt, their value was taken as 



1.0184 0.00004 (t 20) international volts 

 and this value was used as the standard of electromotive force. 22 



21 Callendar and Barnes, Phil. Trans., A, 199, 149 (1902). 



22 See Report of International Conference on Electrical Units and Standards, 

 1908 published in many places, for example, "Science," 28, 743 (1908). 



