165 



a yellow color at once develops and the red precipitate flocculates after a 

 brief interval. At extreme dilutions "where no precipitate forms, a yellow 

 tint is observable. This was suspected to be due to colloidal glyoximine 

 which should be flocculated by another precipitate, in which case, since 

 both silver cyanide and silver cobaltieyanide are white, the red nickel 

 glyoximine would be readily detectable and the delicacy of the test in- 

 creased. The correctness of this view seems to be confirmed by the ex- 

 perimental results detailed below. 



Experimental. 



Solutions and Reagents. NiS0 4 solution, approx. 0.05 molar, from 

 Kahlbaum's "Kobalt-frei" salt, was standardized by electrolysis (0.05008 

 molar) and by precipitation and weighing as nickel glyoximine (0.0496 

 molar). The discrepancy is due probably to a trace of iron which was 

 detected, the removal of which appeared unnecessary for our purpose. The 

 more dilute solutions used were prepared from this by accurate dilution. 



7) Bodlander, Z. anorg. Chem, 39. 227. 



CoS0 4 , approx. O. 1 molar, was prepared by working up residues from 

 cobaltammin salts. Nickel was removed by dimethylglyoxime according 

 to the method we have developed and the solution as used gave no evidence 

 of nickel by any of the tests applied. Electrolysis showed this solution to 

 be 0.0921 molar. Potassium cyanide, 10 per cent, solution. Diniethylgly- 

 oxime, 1 per cent, solution in alcohol. Silver nitrate, 1 per cent, solution. 



Sensitiveness of Dimethylglyoxime as a Reagent for Nickel in 

 Presence and in Absence of Cyanide Iox. 



Ten cc. of NiS0 4 solution of molarity stated in the table below was 

 warmed to about 80° and 1 cc. of the reagent added and a drop or two of 

 dilute ammonia. To the same volume of each NiS0 4 solution two or three 

 drops of KCN were added. At these high dilutions no precipitate was formed. 

 The solution was warmed to 80°, 1 cc. of reagent added and then the AgNOs 

 solution dropwise until a permanent white or pink precipitate formed. 

 The more concentrated solutions gave at once a pink precipitate; the more 

 dilute ones a white precipitate which turned pink on standing. In those so- 

 lutions which required more than one hour to form a precipitate the exact 



