EICHARDS AND CUSHMAN. — ATOMIC WEIGHT OF NICKEL. 337 



is not at all impossible that, in spite of the well known permanence of 

 the smooth bright surface of a nickel-plated object, the spongy metal re- 

 duced by hydrogen might be easily oxidized and dissolved.* The differ- 

 ence in this respect between polished iron and the same metal reduced by 

 hydrogen is well known. Hence Winkler's experiments prove nothing with 

 regard to the behavior of finely divided nickel. The position of nickel 

 on the positive side of hydrogen in the electro-chemical series leads one to 

 expect that it must behave as zinc and iron do, although to a less degree. f 



In order to decide the matter so far as the present work is concerned, 

 we sought to determine experimentally, first, if the purest water is capa- 

 ble of acting on the purest nickel, and secondly, if the hydroxide thus 

 formed is sliglitly soluble in water. To settle the first point, some very 

 pure reduced nickel was thoroughly washed with water, and then digested 

 at 20° for some time with repeated portions of water just purified. In 

 every case nickel could be found in the filtrate, both by means of po- 

 tassic thiocarbonate and by evaporation to dryness. Many repetitions 

 of the experiment with new samples of metal brought always the same 

 result. It is quite possible that galvanic action hastened this oxidation, 

 for of course the nickel was contained in a platinum dish. Since 

 Winkler's dish was evenly coated, the water probably did not touch the 

 plathium in his case, and hence this possible cause of acceleration was 

 absent ; but the difference between the smooth surface and the finely 

 divided surface alone is amply sufficient to explain the difference in 

 the speed of the reaction. 



It will be remembered that Kriiss, in one of his experiments, digested 

 a mass of nickel for a year on the steam bath with water, and obtained a 

 white residue which was the chief basis of his alleged discovery. Our 

 work shows that this residue must have confined not only dissolved por- 

 celain, but also enough nickel to yield the black sulphide, the pale green 

 color, and the electrolyzed metal which led Kriiss so far astray. 



* It is a peculiar household fact that cold water faucets plated with nickel are 

 usually less brilliant than their hot water comrades; this difference may well be 

 ascribed to the slow action of condensed water, even upon polished nickel. Tlie 

 greater tendency to rust shown by cobalt may well be due to the fact that in its 

 case the hydroxide is converted into a higher state of oxidation immediately upon 

 being dissolved, thus giving opportunity for the solution and hence for the forma- 

 tion of more hydroxide. In the case of nickel the thin permanent film of Ni(0H).2 

 probably protects the metal, although its solubility may be no less than that of 

 Co(OH)2. 



t See a paper entitled " Autoxydation," by R. Ihle, Zeitschr. phys. Chem., 

 XXII. 114. 



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