RICHARDS AND LEWIS. — ZINC AND CADMIUM AMALGAMS. 89 



dE_E-h dE _dT 



integrating, In {E-K) = lnT-\- 0= hiKT, 



where C is the integration constant and C = InK, hence 



E = KT -{- h. (4) 



Upon comparing this result with equation (3), which can be written 



E — T -\ one sees that the outcome of this reasoning is simply 



d T ne^ 



dE 

 the proof that if Q is constant -7^, (the temperature coefficient of the 



electromotive force) is also a constant. Thus the electromotive force of 

 any cell of this type should be a linear function of the temperature. 



Materials and Apparatus. 



The materials used in this research were of known purity. The 

 mercury had been twice distilled in vacuo. The zinc and cadmium were 

 prepared by electrolysis from chemicall}^ pure salts. The zinc sulphate 

 had been prepared in this laboratory for atomic weight investigation. 

 The cadmium sulphate was prepared by dissolving the electrolyzed metal 

 in pure sulphuric acid, and crystallizing twice in order to free it from the 

 excess of acid. The amalgams were prepared by mixing weighed 

 amounts of mercury and the metal used and diluting as desired. The 

 amalgams wore weighed and kept under solutions of their sulphates to 

 prevent oxidation. 



Both cadmium and zinc, when electrolyzed from ammoniacal solutions 

 of their sulphates, separate in tree-like forms, varying according to the 

 conditions of electrolysis from large and distinct crystals to finely divided 

 spongy masses. The latter form is produced by the stronger currents 

 and greater dilutions. 



The metal thus made, after suitable washing, was sometimes dried 

 with alcohol and ether and converted into amalgam, or sometimes used 

 at once in the jDure state in the trial cells. The method of using this 

 spongy material as an electrode is described later, on page 90. 



The vessels in which the measurements were made consisted of large 

 H tubes, with their lower extremities drawn out and turned upwards. 

 Platinum wires run in through these fine tubes established the connection 

 with the galvanometer. It was occasionally convenient to use a double 

 H tube, in which one electrode could be connected through the same 

 electrolyte with either of two electrodes. 



