338 



PROCEEDINGS OP THE AMERICAN ACADEMY. 



It is clear that, since no acid was present in the water, the nickel must 

 have been dissolved in the form of hydroxide. In none of our experiments 

 with the purest metal did the solution give an alkaline reaction with 

 phenol phthalein, hence hydroxyl ions must be absent, and tlie hydroxide 

 must be dissolved in a colloidal form. The alkaline reaction sometimes 

 observed by Kriiss and Winkler must have been due to impurities, as 

 Winkler pertinently suggests. Traces of alkali would surely be found in 

 nickel oxide precipitated in glass vessels, even when mercuric oxide was 

 used as the precipitant. 



Nickelous hydroxide, precipitated by alkali and thoroughly washed, 

 possesses at least as great solubility as the hydroxide which is formed by 

 the slow oxidation of nickel. Upon suitable electrolysis, fifteen cubic 

 centimeters of such a cold solution yielded 0.00062 gram of nickel, while 

 another similar portion yielded 0.00057 gram, or about 0.04 gram per 

 litre. Since the solubility is a colloidal one, its limit is indeterminate; 

 hence no elaborate attempt was made to discover its exact amount. It 

 is well known that the presence of other salts in the solution diminish 

 this kind of solubility, but the small amount of sodic bromide present in 

 this case was insufficient to produce any considerable effect. Undoubtedly 

 the fact that the solubility is colloidal and uncertain is responsible for 

 the conflicting statements of the various authorities and handbooks.* 



This solubility of nickelous hydrate is the circumstance which obliged 

 us to determine the residue of sodic bromide through argentic bromide, 

 instead of simply by evaporating the wash-waters poured off from the 

 nickel and weighing the residue. This necessity is made clear by the 

 foUowius table. 



»T c Tf ■ I... c Weight of Residue 

 No. of Weight of extracted bv Water 



Aual. 



Nickel, 

 grams. 



0.805 



6 



7 1.488 



8 0.G07 



and dried at 105-' 

 grams. 



0.00330 

 0.00895 

 0.00400 



Weight of 

 AgBr. 



grams. 



0.00410 

 0.01398 

 0.00568 



Weight of NaBr 

 calculated 

 from AgBr. 



grams. 



0.00225 

 0.00767 

 0.00311 



Weiglit un- 

 accounted for. 



grams. 



0.00105 

 0.00128 

 0.00089 



In order to prove that this large percentage of unexplained residue 



* Finkener (Handbuch der Anal. Cliem. von Rose, 6te Auflage von Finkener, 

 II. 136); Busse (Zeitschr. Anal. Chem., XVII. 60); Fresenius (Quant. Anal., 

 1877-1887, II. 393, 823) ; Roscoe and Schorlemmer (A Treatis^e on Chemistry, Vol. 

 II. Part II. p. 149); Winkler (loc.cit.); Kriiss {loc.cit.); etc. Temperature is a 

 circumstance which produces great effect on this kind of solubility, heat being apt 

 to coagulate the dissolved material. 



