502 Transactions. 



agreement, as the following figures indicate : Amount deposited after four 

 hours, 0-3088 grim, 0-3087 grim, 0-3090 grim, 0-3084 grm., 0-3069 grim, 

 0-3085 grm. ; yielding a mean value of - 3084 gun. when 5 c.c. of the standard 

 solution with the ammonia and ammonium sulphate (to increase the con- 

 ductivity) added was electrolyzed. 



Series 1. 

 (Solution containing no nitrate.) 



The first series of experiments was conducted with the solution as 

 indicated above, in the absence of nitrate, with the object of obtaining a 

 curve showing the rate of deposition of the metal. This was effected by 

 interrupting the electrolysis after it had proceeded a definite time, and 

 then washing, drying, and weighing the cathode in the usual manner. At 

 the same time, during the course of the electrolysis, readings were taken 

 continuously of (i) ammeter, (ii) P.D. across the terminals of the electrolytic 

 cell, (iii) P.D. at the cathode. 



Ammeter Readings. — ■ These were noticed to exhibit slight variations, 

 though they remained practically constant throughout each experiment. 

 A small initial rise was invariably noticeable, due probably to increase in 

 temperature as a result of the ohmic resistance encountered, and towards 

 the conclusion of an experiment a diminution was always observable. The 

 extent of these fluctuations never exceeded 0-10-15 amp., and to facilitate 

 subsequent investigations it was decided to maintain the current at a con- 

 stant value by inserting an adjustable resistance in the circuit. It did not 

 seem possible to deduce anything of importance from a study of these small 

 variations. 



Voltmeter Readings. — -The readings of the voltmeter were found to exhibit 

 a much more marked fluctuation. A considerable number of experiments 

 were conducted so as to confirm the unusual nature of the variations, and it 

 was found that they could be divided into three stages : (a) Very slight rise 

 during the first hour, followed by a return to the initial value ; (b) period 

 during which the voltmeter remained approximately constant ; (c) towards 

 the end of an experiment a distinct rise in P.D. could be detected, 

 amounting to 0-2-0-4 volt. These stages were not always clearly defined, 

 though the final rise was almost invariably observed. This would corre- 

 spond to increased resistance between the electrodes, and, on account of the 

 presence of the ammonium sulphate, it could not be explained by a dimi- 

 nution in the conductivity of the solution. Further, it is noticed after 

 almost all the nickel has been deposited and only traces remain in solution. 

 The removal, then, of these last traces of the metal must involve the ex- 

 penditure of more electrical energy and indicate the presence of polarization 

 phenomena. Marshall (loc. cit.) suggests that " a film of some other substance 

 is deposited giving a higher polarization effect. At first this is replaced more 

 or less by nickel, and occasionally breaks down, as shown by the lapses to 

 the original potential, possibly on account of the richer solution being 

 brought against it by convection currents, but it ultimately becomes per- 

 manent when the nickel deposition is completed." In the case of this 

 investigation, as in that of Marshall, the final rise appears to be an indication 

 that the deposition is complete. 



Potential Difference at the Cathode. — To study the changes in P.D. at the 

 ■cathode the arrangement depicted in fig. 1 was employed. 



The composite cell consisted of calomel electrode, Ni-NiS0 4 (ammon.). 



