222 JONES AND SCHUMB, 



limb of the electrode. The amalgams used contained approximately 

 55% of thallium. They were heated under water until liquid and 

 then allowed to cool, forming a two-phase amalgam. 



The results of these measurements are tabulated below. Each 

 thalHum electrode and each calomel electrode were prepared sepa- 

 rately, the cell being entirely dismantled between each two determina- 

 tions. The thallous chloride solutions were saturated anew each time, 

 and fresh materials were also used in making up each calomel electrode; 

 so that the values obtained were entirely independent. 



In the work at 0°, the concentrations of the potassium chloride 

 solutions used were adjusted for the change in temperature. The 

 saturation of the thallous chloride solutions at 0° was attained from 

 above as well as below the solubility of the salt at that temperature. 



The check measurements at 0° upon the normal and decinormal 

 electrodes were carried out in a cell of the type shown below in 

 Figure 6. The 25° value has been fixed with accuracy by a number 

 of experimenters. *° 



In the following tables each line gives the measurements on an 

 independent cell, the cells being completely dismantled each time 

 and set up again with new electrodes and fresh solutions. The 

 two measurements on each line refer to the two different thallium 

 or thallium amalgam electrodes in each cell measured against the 

 same calomel electrode. The figures given are actual measured poten- 

 tials without any corrections, the calomel electrode being always 

 positive. 



From this table the normal potential of the thallium electrode is 

 calculated to have the following values, which refer to the metal 

 electrode only: 



At 25°: En = + 0.6188 V.) . , ^^ /i t^i + j 

 At 0°: E. = + 0.5885 ) "^"^"^^ ^/^ ^^'''''^'- 



Lewis, Brighton, and Sebastian *^ in a study of the calomel electrode 

 conclude that the value of the electromotive force between the tenth- 

 normal and the normal calomel electrode at 25° is —0.0529 volt. In 



40 This enables us to determine the temperature coefficient of the potential 



difference between the decinormal and normal calomel electrodes over the 



range 0°-25°; assuming the temperature coefficient to be independent of the 



.,,.., , , -0.0533 - (-0.0489) nnnniQ 



temperature m this interval we have: — =—0.00018 



volt per degree. (See p. 225.) 



41 G. N. Lewis, T. B. Brighton and R. L. Sebastian, Jour. Amer. Chem. Soc, 

 39, 2245 (1917). 



