W. Gibbs on the Hexatomic compounds of Cobalt. 197 
On the other hand, however, I have already shown (§ 3) that 
salts of this radical are formed in large quantity, together with _ 
a smaller proportion of the octamin nitrate, by the action of a 
mixture of potassic nitrite and ammonia upon cobaltic nitrate 
in presence of air; but that xanthocobalt is exclusively formed 
by the action of the same mixture upon a solution of ammonic 
and cobaltic sulphates. I am unable to offer any plausible ex- 
planation for the difference of the products in the two cases. 
When cobaltic nitrate, ammonic nitrite and ammonia are 
mixed and placed in a tightly-corked bottle, no action whatever 
appears to take place, even after the mixture has stood some 
2Co(NO,),-+-10NH,4-2NO,. NH, + PbO.=Co,(NH;):(NO3)2 
(NO,),+PbO+(N H,).0. 
Potassic hypermanganate may also be employed as an oxidizing 
agent, but is less convenient. The experiment just detailed 
appears to me to render it most probable that in the action of 
the red gases upon salts of cobalt in presence of ammonia, the 
resulting salts of xanthocobalt are not formed by the direct 
union of the cobaltic salt with ammonia and nitroxyl, but that 
ammonic nitrite is first formed, and that the oxygen necessary 
simple cases of double decomposition, a particular instance of 
which, covering in substance the whole ground, may ex- 
pressed by the equation: 
Co, (NH,), .(NO,)¢+2NH,-NO,=00,(NHs)10(NO2)s 
910 NO MO, ), + 2NOg NA. 
Salts of xanthocobalt are always formed when salts of pur- 
pureocobalt and roseocobalt are heated or even digested in the 
cold with alkaline nitrites. I have made a special study of the 
action of potassic and sodie nitrites upon chloride of purpureo- 
cobalt, the details of which are as follows: 
Action of sodic and potassic nitrites upon chloride of pur- 
Ppureocobalt.— A quantity of chloride of purpureocobalt was 
dissolved in boiling water, with a little free acetic acid to prevent 
decomposition, and added to a hot solution of potassi¢ nitrite 
in excess. The dark brown-red solution was evaporated at a 
