Vol. VI, No. 2.] The Electro-chemical Equivalent of Nickel. 41 



[N.S.] 



disengagement of gases with an unpleasant smell took place 

 from the surface of both the electrodes, especially from the 

 Cathode, and the value of the e.c.e.' s as determined from the 

 deposits were much lower than the theoretical value -0003043. 

 The best value obtained was -0002528. Saturated solutions 

 gave no better results. 



As it was thought that the complexity of the action in 

 nickel ammonium sulphate might be the cause of the bad 

 results, sulphate of nickel was the next salt worked with. At 

 first a weak solution of the salt was taken, but the disengagement 

 of gases, though much less than with the double sulphate, was 

 still considerable. Strong solutions gave slightly better results. 

 Lowering the difference of potentials between the plates 

 reduced the evolution of gases, but owing to the high electrolytic 

 resistance of nickel sulphate the current fell too low for accu- 

 rate measurements with the apparatus employed. 



Effect of Purity of the Salt. 



The e.c.e.' s obtained in these preliminary experiments 

 were much below the theoretical value and differed widely from 

 one another. In every case there was copious evolution of gas 

 from both the plates. 



As these experiments showed that there was no prospect 

 of getting constant values for the e.c.e., by means of small 

 variations of current and voltage alone, attention was drawn 

 to the materials employed. 



The nickel sulphate crystals in stock were purified by re- 

 peated crystallisations. Two separate solutions were thus 

 prepared, one the " pure stuff" consisting of the first few 

 crops of crystals dissolved in distilled water, the other, the 

 " impure stuff", i.e., the mother liquor left after the removal 

 of the several crops of crvstals. (S. G. of pure stuff 1-318 at 

 24 3 8 C, volume 216 c. c. S. G. of impure stuff 1-306 at 24°8 C. . 



volume 750 c. a). 



It may be mentioned here that all the crystals obtained 



were of the prismatic or neutral type except those of the last 

 crop, which were thrown down as the pyramidal or acid 

 variety. These latter were not added to the "pure staff '• but 

 redissolved in the mother liquor with addition of a little dis- 

 tilled water, and the process of separation by crystallisations 

 was not continued any further. The last set of crystals gave 

 an important clue as to the acid character of the mother liquor, 

 iA f the " impure stuff f \ an indication which was subsequently 

 found very useful. A number of observations were made 

 with both the stuffs in order to examine the effect of purifica- 

 tion by crystallisation. 



It was found that a much better value of the e.c.e. was 

 obtained with the pure than with the impure solution, me 



