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W. Gibbs on the Hexatomie compounds of Cobalt. 295 
requires cobalt, 21-99 per cent, and CrO,, 48°32 percent. The 
formation of the neutral chromate is expressed by the equation : 
Co,(NH,),5(NOs),+20r0,K,+OH,=Co, (NH) 9-0. (CrO,), 
44KNO,+2NO,H. 
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 purpureocobalt, a pink tungstate of pur- 
pureocobalt is formed, and the liquid then gives a strong aci 
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 formula, and the precipitate ap- 
peared to be a mixture of the chromate described, Co, s)ie 
O.(CrO,),, and the iodo-chromate, Co, (NH,), o1,(CrO,),- By 
digesting powdered chloride of purpureocobalt with neutral 
potassic chromate, Braun obtained a dark brown-red powder, to 
which he gives the formula Co,(NH,), .(CrO,);- According 
to the same writer, when powdered chloride of purpureocobalt is 
added, in small portions at a time, toa concentrated solution 
of potassic dichromate, a beautiful crystalline powder is formed, 
which has also the formula Co,(NH,), ,(CrO,)>- In this case 
chromic acid, CrO,H,, must be set free. When a solution of 
potassic chromate is added to one of chloride of purpureo- 
cobalt, the crystalline precipitate formed, according to my obser- 
vations, always contains chlorine. My analyses led, however, 
in this case also, to no definite formula, but pointed to a mix- 
ture of the chromate, Co,(NH,), ,-0.(CrO,)., and the chloro- 
chromate, Co,(NH,), ,Cl.(CrO,)2- Braun has also described. 
a salt, to which he gives the formula 9NH,.Co,0,.3CrO, + 
2NH,Cl, which I should write Co,(NH, ,(CrO,);+2NH,Cl, 
but the analyses are incomplete without a determination either 
of ammonia or of nitrogen 
rates in small, indistinct erystals of a dark brick red color, = 
bronze reflections. It is somewhat soluble in cold, and dis- 
solves readily in boiling, water. Of this salt 
0°6031 gr, gave 0°0747 gr. cobalt=12°38 per cent. ee 
0°7101 a ies 11252 gr. CrO, Ba=67°71 per cent. (Chromiam= 
52°2,) 
= t: at 
0°6295 or. lost. at 105° C., 0°0077 gr. water=1'22 per cen'; 
120° C., 0-0118 gr.=1°87 per cent; and at 133° C., 0 0166 
gr.=2°64 per cent. 
