OF THALLIUM, INDIUM, AND TIN 15 



THE CELL. 



The multiple cell used in all the measurements of electromotive force is 

 shown in fig. 4. This apparatus, devised by Richards and Forbes, must be 

 very carefully annealed, for even at the best the glass receptacle is very 

 fragile. The body of the vessel is used to hold the electrolyte ; the four 

 cups contain the amalgams to be measured. The advantage of the four 

 cups is obvious: six different measurements may be made at one filling, 

 and at the same time important checks can be secured on the accuracy of 

 the readings. 



Fig. 4. Amalgams in Cell ready for Potential Measurement. 



The glass receptacle was carefully cleaned and dried, and fused at A to 

 the delivery tube of an apparatus supplying pure hydrogen. A vacuum 

 pump was now attached at S 2 and the whole cell exhausted as far back as 

 the stopcock 6\. The tops of the tubes, B, C, D, and E were closed with 

 small pieces of rubber tubing and glass rod. When the pressure had been 

 reduced to about 20 mm., the stopcock S 2 was closed and the cell allowed 

 to fill with hydrogen through S^. This was repeated four times. The 

 glass rod was now removed from one of the tubes and the fine tip of a 

 pipette, containing the proposed electrolyte, inserted. The issuing stream 

 of hydrogen prevented the diffusion of air into the cell. When the vessel 

 was about half full of the aqueous solution, the pipette was withdrawn and 

 the stopper was replaced. In the same manner suitable amounts of the 



