2O ELECTROCHEMICAL INVESTIGATION OF LIQUID AMALGAMS 



400 ohm coils ; and the deviation of these amounted to only 0.000002 and 

 o.oooooi volt respectively. The boxes B and C were of the same quality 

 as A and a preliminary standardization showed them to be fully as accu- 

 rate. Since the resistances in B and C need be known only one-tenth as 

 accurately as those in A, any corrections on these boxes would be super- 

 erogatory. The one important point, that 1000 ohms in A should be 

 exactly one-ninth of the 9000 ohms in B, within o.oi per cent, was demon- 

 strated. 



The standard Weston cells were made up from pure material as recom- 

 mended by Hulett. These cells were compared with one another and also 

 with three similar cells kindly loaned by Dr. H. L. Frevert. They all 

 furnished the same value to within o.oooi volt at 20, and for their value 

 the electromotive force 1.0184 was accordingly assumed. 



The improved potentiometer described above appeared to be accurate to 

 within a microvolt (o.oooooi volt) a high degree of precision. 



ELECTROMOTIVE FORCE BETWEEN THALLIUM AMALGAMS. 



With the apparatus and materials which have been described, measure- 

 ments upon a variety of amalgams were executed. The description of a 

 preliminary experiment will be given in detail, in order that the method 

 may be more thoroughly understood. Amalgam I was prepared in the 

 closed apparatus by depositing into 180.557 grams of mercury the amount 

 of thallium equivalent to 0.9473 grams of silver (deposited in a coulometer 

 in the same circuit), that is to say, 1.7915 grams of thallium, if silver and 

 thallium are assumed to have the atomic weights of 107.88 and 204.03 

 respectively. Hence the amalgam contained 0.9822 per cent of thallium 

 by weight. 



One portion of this amalgam was introduced into one cup of the multiple 

 cell, and another weighed portion was introduced out of contact with air 

 into another cup, being diluted by the addition of a weighed amount of the 

 pure mercury, which had been preserved in hydrogen as previously 

 described. The second cup contained 36.513 grams of mercury, and 

 received 25.721 grams of amalgam. It is easy to calculate that the dilute 

 amalgam must have contained 0.4059 per cent of thallium. In order to 

 mix thoroughly the amalgams and mercury in the second cup, the cell was 

 gently shaken for some time, great care being taken to avoid any splashing 

 from one cup to another. The cell was then introduced into the 30 ther- 

 mostat and, after it had acquired the temperature of the bath the readings 

 were begun. Two measurements of the cell gave values of 25.235 and 

 25.238 millivolts respectively, in mean 25.237. 



The potential remained very constant over a considerable interval of 

 time. Two entirely separate measurements taken with the same cell 48 



