THE CELL AND ITS MANIPULATION. 21 



amalgam, then with S 3 open to the vacuum a rapid stream of rarefied 

 hydrogen was passed through the solution for some time. It is believed 

 that this process removed the remaining air. Finally S 3 was closed, and F 

 allowed to fill with hydrogen, after which the solution was drawn up into B 

 in the usual way. When the connection at A was fused off, the outlet of B 

 was drawn out into a fragile capillary and sealed. Of course, when the 

 solution was wanted, its weight was not sufficient to draw it out. To follow 

 it up with hydrogen a well-cleaned rubber tube delivering hydrogen was 

 forced over the fragile capillary ; when this was broken communication with 

 the gas generator was established. 



Some previous investigators have allowed their electrolytes to stand over 

 amalgams for some time before using it in the cells. 42 Zinc sulphate, fifth 

 normal, was left in Jena glass over amalgam of the purest materials for 

 several weeks before the first measurements, with occasional stirring. Per- 

 haps the partial absorption of dissolved oxygen by the amalgam thus attained 

 is helpful. However this may be, a pure sulphate solution freed from air by 

 a stream of hydrogen can be used with perfect safety without putting it 

 through this lengthy process. 



THE CELL AND ITS MANIPULATION. 



The cells used in the potential measurements must now be described. 

 Figure 4 gives a good idea of the appearance of one of these just after a 

 determination. The other cell used was different in one respect its cups 

 were all the same size. Very careful annealing of this apparatus is neces- 

 sary. The advantages of this arrangement are marked. Four different 

 amalgams can be introduced at one filling, and six direct potential measure- 

 ments obtained under exactly the same conditions. Great economy of time 

 and material are thus secured, and more important still, valuable checks on 

 the accuracy of the measurements. These will be discussed later. The prin- 

 ciple might, if necessary, be extended to cells containing even more cups. 



The cell, clean and dry, was suitably supported in the thermostat, and 

 the tube A fused to the outlet of a hydrogen generator similar to that shown 

 in figure 2, and like it made of a single piece of glass. A double gridiron 

 of glass tubing allowed considerable play without the introduction of a rub- 

 ber connection, but the tubes B, C, D, E, were closed by clean rubber tubes 

 and pieces of glass rod. The rubber surface exposed to the atmosphere of 

 the cell was very small. The system as far back as the stopcock S x was 

 evacuated through S 2 by a very efficient mechanical hand pump, and then 

 filled with hydrogen through S x . After this operation had been performed 



42 Richards and Lewis, Proc. Am. Acad., 34, 87 (1898). 



