190 W. Gibbs on the Hexatomie compounds of Cobalt. 
doubtless yield an ample return. 
. Action of ammonic nitrite on salts of cobalt.—To obtain a 
clear view of the nature and mode of formation of the salts of 
xanthocobalt, I have carefully studied the relations of ammonic 
nitrite to salts of cobalt under different conditions. This sub- 
ject has already been examined by Erdmann, and in my 
laboratory by Sadtler. Erdmann found that when a neutral 
solution of cobaltic chloride is mixed with a neutral solution 
of ammonic nitrite no turbidity ensues, but after spontaneous 
evaporation in the air a salt crystallizes, with the formula, as 
Erdmann writes it (old style): 
Co,0,.2NH,, 3NO,+NH,0, NO,. 
This salt is isomorphous with the corresponding potassium salt, 
the crystals belonging to the rhombic system. Erdmann does 
not explain the reaction which takes place in the formation of 
this or the corresponding potassium salt, and regards the 
compounds in question as double salts) When slightly acid 
solutions were employed, Erdmann obtained, in addition to the 
above mentioned salt, an ammonic salt corresponding to Fis- 
cher’s salt, Co.(NOz)(NH,).+30H», as we should now write it. 
The existence of this salt was first remarked by Genth and 
myself.* Sadtler studied the action of ammonic nitrite on 
acid solutions of cobaltic chloride, and obtained two salts hav- 
ing respectively the formulas: 
Co,(NO,) ,)(NH,),+20H; 
Co, (NO) ,2(NH,),+20H,, 
but did not observe the formation of Erdmann’s ammonium salt. 
In repeating these experiments I always obtained Erdmann’s 
ammonium salt, CoNH,),(NO,)(NHy,),, in largest quantity. 
The crystals are uncommonly beautiful and well defined. Of 
these crystals 
0°3390 gr. gave 0°1783 gr. SO,Co=20°02 per cent. 
The formula requires 20-00 per cent. In one experiment, in 
which a little free acetic acid was present, I obtained large dark 
sherry-wine colored prismatic erystals, which after solution and 
recrystallization gave only very thin lozenge-shaped tabular 
'  * This Journal, 2d Series, vol. xxiv, p. 86. 
