RICHARDS AND CUSHMAN. — ATOMIC WEIGHT OF NICKEL. 105 



produced was changed to bromide and sublimed in the manner already 

 described. The pure substance thus prepared is designated below as 

 number II. ; it also served for two of the earlier analyses. 



The further purification of the sample of nickel obtained by the process 

 of IMond, Langer, and Quincke, at first proceeded exactly in the steps 

 just described; except that no attempt was made to remove cobalt, 

 since none was present. After it had reached the stage of treatment 

 represented by the last hydroxide obtained above, the material was con- 

 verted into the sulphate and subjected to electrolysis out of an am- 

 moniacal solution in a platinum dish. The object of this procedure was 

 of course to free the nickel still more effectually from the alkalies, silica, 

 and many other impurities which are not precipitated on the cathode. 

 The bright heavy deposit of pure nickel was dissolved, with a great deal 

 of difficulty, in redistilled strong nitric acid ; and the excess of acid was 

 driven off by evaporation. Ammonia and a large excess of pure water 

 were now added, and the solution was boiled until the basic hydroxide 

 was completely precipitated. This was subsequently changed to metallic 

 nickel and then into the sublimed bromide, in the manner already de- 

 scribed, and the resulting material, labelled III., served for a large 

 number of analyses. A small portion of it, that used for Experiment 8, 

 was resublimed. 



The sample of material used for the final analyses was even more care- 

 fully purified than this, however. A quantity of the pure nickelous 

 oxide of about the grade of purity of sample III., coming originally from 

 the Mond nickel, was dissolved in sulphuric acid, and the solution was 

 made alkaline by passing in pure ammonia gas, in a platinum dish. 

 When most of the nickel had been deposited electrolytically from this 

 solution, the jDortion remaining in the electrolyte was thrown away. The 

 bright coating of nickel was washed, pure dilute sulphuric acid was put 

 into the dish, and with reversed poles a strong current was sent through 

 the solution until nearly but not quite all of the nickel was dissolved. 

 The solution was then decanted into another dish, ammonia was passed 

 in until the precipitate formed had redissolved, the poles were again re- 

 versed, and then nickel was once more almost all deposited. This cycle 

 of operations, which gives an excellent method of fractionation, was 

 repeated three times. The final deposit of nickel was dissolved by 

 filling the platinum dish with pure dilute nitric acid and reversing the 

 poles. Only one who has tried dissolving a deposit of nickel on a plati- 

 num dish, even in strong nitric acid, can appreciate the ease, cleanliness, 

 and convenience of this method of procedure. The solution of nickel 



