296 W. Gibbs on the Hexatomic compounds of Cobalt. 
At 183° C. the salt was slightly decomposed. Between 133° 
and 145° C. it lost 4:46 per cent with partial decomposition. 
These analyses correspond to the formula Co,(NH,), ,(Cr,0;); 
+0OH,. 
Calculated. Found. 
Cobalt, 2 12°35 12°38 
Or50,; 3 6707 2 STF 
Waiter, 1 1°88 1°87 
The salt was dried for two weeks in pleno over sulphuric acid. 
In preparing nitrate of purpureocobalt by Mr. Mills’ process, a 
by potassic dichromate, I obtained, besides the nitrate, a large 
quantity of beautiful orange-red crystalline scales, with g 
reflections. The crystals were easily purified by recrystalliza- 
tion. ey are readily soluble in hot water, and crystallize 
from the solution almost completely on cooling. The formula 
of this salt is Co,(NH,), ,(Cr,0,),+50H,, as the following 
analyses show : 
0°6366 gr. gave 0°0735 gr. cobalt=11°54 per cent. 
0°6447 gr. gave 0°2888 gr. CrO, 63°31 per cent Cr,O,. 
071740 gr. gave, up to 139° C., 0°0125 gr. water=7°19 per cent. t 
0°0800 gr. gave, up to 145° C., 0°0082 gr. water—=10°25 per cent. 
ean, 8°72 per cent, 
In the last water determination the salt was slightly decom- 
posed. The formula requires 
Found. 
Cobalt, 2 11°48 11°54 
r,0,, 38 68°20 63°31 
Water, 6 8°76 8°72 (mean.) 
The difference in appearance and in the number of atoms of 
water of the dichromate of purpureocobalt may possibly arise 
from the fact that, in one case, a solution of the nitrate of pur- 
pureocobalt was poured into one of potassic dichromate in ex- 
cess; in the other, the nitrate was presented to the dichromate 
as fast as formed—in some sense in the nascent state. But it 
is singular that the two hydrates are not the same after recrys- 
tallization. A solution of potassic dichromate gives, with one 
of chloride of ool ganar adark red crystalline precip! 
of which pointed to a mixture of Co,(NH;,),o 
and Co,(NH,), ,.Cl,.(Cr,O,),. I did not succeed in 
(To be continued.) 
es 
