Vogel's Reaction for Cobalt 



149 



traces of iron interfered less when the sodium salt was used. This is 

 in accord with the observation of Rosenheim and Cohn' that of the 

 three alkali-ferric thiocyanates, R:,Fe(SCN) ,;, prepared by them the 

 sodium salt is most stable and least decomposed by aqueous ether into 

 Fe(SCN)3, which is soluble in ether and NaSCN insoluble in ether. 



B. The Vogel Test in acid sohition. The effect of varying a single 

 component of the test solution while keeping the others constant is 

 shown in the tables following. 



TABLE 1. Effect of acid concentration. 



0.01 mg. Co, 1 cc. 4 N NH4SCN, 0.3 cc. C.HsOH, 1.2 cc. (C.>H,)jO; total 

 volume 5 cc. 



TABLE 2. p]ffect of thiocyanate concentration. 

 0.01 mg. Co, 0.8 cc. 5 N HCl, 0.3 cc.CHsOH, 1.2 cc. (C-HO^O; total vol., 



Normality of thiocyanate 

 in 5 cc. 

 0.0 

 0.08 

 0.4 

 0.8 



1.36 



^ Loc. cit. 



Color in 



alcohol-ether layer 



none 



none 



faint blue 



maximum blue 



maximum blue 



