316 Browning and Hartwell — Nickel from Cobalt. 



Art. XXXII. — On the Qualitative Sejyaration of Nickel from 

 Cobalt by the action of Ammonium Hydroxide on the 

 Fewicyanides ; by Philip E. Browning and Johjst B. 

 Hartwell. 



[Contributions from the Kent Chemical Laboratory of Yale University — XCVIL] 



Some years ago F. W. Clarke* suggested a method for the 

 separation of nickel from cobalt depending upon the solvent 

 action of ammonium hydroxide upon the precipitated ferri- 

 cyanides. The method may best be described by quoting from 

 the original article : " To the slightly acid solution containing 

 the two metals, I first add an excess of ammonium chloride. 

 This causes the cobalt precipitate, which otherwise would run 

 through the filter, to fall in a denser state, and also of a much 

 darker color, often nearly black. I then add the potassium 

 ferricyanide until the precipitation is complete, and afterwards 

 agitate strongly with a considerable excess of ammonia. Upon 

 filtering, all the cobalt remains upon the filter, being recog- 

 nized by the characteristic color of the precipitate, and the 

 nickel is readily detected in the filtrate, by means of ammo- 

 nium sulphide. If, upon filtering, the portion at first running 

 through is turbid, it may be disregarded, or returned to the 

 filter, that which filters through subsequently being almost 

 invariably clear." 



In making a study of this method we found two serious 

 objections ; first, the practical impossibility of obtaining a good 

 filtration from the cobalt ferricyanide, even in the presence of 

 the ammonium chloride, and, second, the large amount of sul- 

 phur thrown clown when ammonium sulphide was added to 

 the filtrate containing the nickel with the excess of ferricyanide. 



Our first attempt was to secure, if possible, a complete sepa- 

 ration of the precipitated cobalt ferricyanide and the dis- 

 solved nickel by filtration. This we were able to accomplish 

 by the addition of a small amount of a solution of an alumi- 

 num salt to the original solution which held back the cobalt, 

 and, as experiment showed, allowed the complete solvent action 

 of the ammonium hydroxide upon the nickel salt. Amounts 

 of nickel as small as 0*0001 grm. were detected, when mixed 

 with the aluminum salt, by precipitating as ferricyanide, 

 extracting with ammonium hydroxide, and testing in the man- 

 ner to be described. 



On turning our attention to a possible improvement in the 

 method for the detection of the nickel, it was found that when 

 the ammoniacal solution of the nickel ferricyanide was treated 



* This Journal, xlviii, 6T. 



