163 
DETECTION OF NICKEL IN COBALT SALTS. 
A. R. Mippietron anp H. L. MiILuer. 
The use of dimethylglyoxime as a reagent for the detection and determina- 
tion of nickel, discovered by Tschugaey! in 1905 and developed by Brunk,? 
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 
4,000,000 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. Hither because the 
nickel salt is soluble in this compound, or, as 1s 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. Treadwell,* following a suggestion of Tschugaeyv, accomplishes 
this result by 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 
1Ber. 38, 2520. 
2Z,. angew, Chem., 20, 3444. 
3Analyt. Chem., Vol. I. 151. (7te Aufl.) 
