163 



Detection of Nickel in Cobalt Salts. 



A. R. MlDDLETOX AXD H. L. MlLLER. 



The use of dimethylglyoxime as a reagent for the detection and determina- 

 tion of nickel, discovered by Tschugaev 1 in 1905 and developed by Brunk, 2 

 has become a general practice. For simplicity of manipulation and freedom 

 from interference this reagent is unrivalled; the brilliant scarlet color and 

 extreme insolubility of the nickel glyoximine renders possible the detection 

 of one part of nickel ion in at least 350,000 parts of water. By a modified 

 method of applying the reagent, "which was developed in the course of this 

 investigation, we found it possible to detect one part of nickel ion in more than 

 ■1.000,000 parts of water. 



For detection of traces of nickel in cobalt salts this reagent, hitherto, 

 has not been very satisfactory. Cobalt combines with dimethylglyoxime to 

 form an extremely soluble compound of brown color. Either because the 

 nickel salt is soluble in this compound, or, as is much more probable, because 

 the cobalt appropriates most of the reagent, no nickel is precipitated by 

 ordinary amounts of reagent from cobalt salt solutions, even though a con- 

 siderable amount is present. The object of this investigation was to devise 

 a method by which the cobalt ion should be suppressed, thus permitting the 

 reagent to react with nickel only thus avoiding the necessity for large amounts 

 of reagent. TreadwehV following a suggestion of Tschugaev, accomplishes 

 this result bj T transforming the cobalt salt into a cobaltic ammin by strong 

 ammonia and hydrogen peroxide before adding dimethylglyoxime. We 

 shall show that this method is unsatisfactory and fails when much cobalt 

 is present. 



The most striking differences in the chemical behavior of nickel and 

 cobalt are (1) the greater readiness of oxidation to the trivalent condition 

 and (2) the greater stability of the complex ions, both positive and negative, 

 of cobalt. Of the various complex ions formed by cobalt the most stable are 

 the complex cyanides, that of trivalent cobalt being decidedly more stable 

 than that of bivalent cobalt. Nickel forms soluble complex cyanides of a 



iBer. 38. 2520. 



2Z. angew, Chem., 20, 3444. 



^Analyt. Chem., Vol. I. 151. (7te Aufl.) 



