36 PROCEEDINGS OF THE AMERICAN ACADEMY 



requires cobalt, 21'99 per cent, and CrO^, 43'32 per cent. The forma- 

 tion of the neutral chromate is expressed by the equation : — 



Co,(NH3),,(N03), + 2CrO,K, + OH, = Co,(NH,),„.0.(CrOJ, + 



4KNO8 + 2NO3H. 



The nitric acid set free dissolves a portion of the chromate forming the 

 dichromate, which remains in solution. When a solution of neutral 

 potassic tungstate, WO^K,, is digested with dry neutral nitrate of pur- 

 pureocobalt, a pink tungstate of purpureocobalt is formed, and the 

 liquid then gives a strong acid reaction with litmus. The reaction is 

 probably the same as that given above for the chromate. 



Potassic iodide gives a dull red crystalline precipitate with neutral 

 chromate of purpureocobalt in solution. The analyses of this salt led 

 to no definite formida, and the precipitate appeared to be a mix- 

 ture of the chromate described, Co2(NH3)^o.O.(Cr04)2, and the iodo- 

 chromate, Co2(NH3)^J,(CrOj2. By digesting powdered chloride of 

 purpureocobalt with neutral potassic chromate, Braun obtained a dark 

 brown-red powder, to which he gives the formula Co2(NH.;)j^(Cr04)3. 

 According to the same writer, when powdered chloride of purpureo- 

 cobalt is added, in small portions at a time, to a concentrated solution 

 of potassic dichromate, a beautiful crystalline powder is formed, which 

 has also the formula Co2(NH3)jy(CrOj3. In this case chromic acid, 

 CrO^Hg, must be set free. When a solution of potassic chromate is 

 added to one of chloride of purpureocobalt, the crystalline precipitate 

 formed, according to my observations, always contains chlorine. My 

 analyses led, however, in this case also, to no definite formula, but 

 pointed to a mixture of the clu-omate Co2(NH3)jo.O.(CrO^)2, and the 

 chloro-chromate, Co2(NH3)jQC]2(CrOj2- Braun has also described a 

 salt to which he gives the formula 2NH3.Co203.3Cr03+ 2NH,C1, 

 which I should write Co2(NH3)2(CrOj3-|- 2NH^C1, but the analyses 

 are incomplete without a determination either of ammonia or of 

 nitrogen. 



Dichromate. — A solution of potassic dichromate gives, with one of 

 nitrate of purpureocobalt, a granular red precipitate, which may be 

 recrystallized by solution in boiling water, to which a little acetic acid 

 has been added. The salt then separates in small, indistinct crystals 

 of a dark brick-red color, with bronze reflections. It is somewhat 

 soluble in cold, and dissolves readily in boiling, water. Of this salt 



