122 W. Gibbs on the Hexatomic compounds of Cobalt. 
* 
prepare it from the crude sulphate by double decomposition 
‘with baric nitrate. The sulphate is to be boiled with a small 
ammonic nitrate. It is much more convenient, however, to 
s 
sulphate, though cold water takes up but little. Boiling water 
andl ilute acid solutions dissolve it more readily. ‘The reac- 
tions of the base may be studied most conveniently with this 
salt. The formula of the nitrate is 
Coz (NH3).(NO2),(NO3)2 
as the following analyses show : 
0°2405 gr. gave 0°1333 gr. CoSO, = 21°10 per cent cobalt. 
0°6564 gr. gave 0°2484 gr. water = 4:21 per cent hydrogen. 
0°6148 gr. gave 173°5 c.c. nitrogen at 4°°5 C. and 762°2™™-=34'83 *& 
Calculated. Found 
Cobalt 2 118 20°99 21°10 
Hydrogen 24 24 4°27 4°21 
Nitrogen 14 196 34°88 34°83 
xygen 14 224 39°86 
562 100°00 
The nitrate explodes, though not very violently, on being heated. 
Its solution gives with a potassic ferrocyanide no precipitate at 
rst, but after some hours beautiful garnet-red acicular erys 
are formed. It is most easily distinguished from the nitrate of 
Xanthocobalt by its crystalline form and by the extremely 
characteristic precipitates which its solution yields with potassi¢ 
hyperiodide and with potassic chromate. 
Chromate.—When a solution of potassic chromate is added 
to one of the nitrate of the octamin’series a most beautiful 
lemon-yellow salt is formed, which separates almost immediately 
in very brilliant scales which appear to belong to the quadratic 
system, and to be isomorphous with the sulphate. The salt 18 
but slightly soluble in water. Its marked crystalline form ren- 
ders it valuable as distinguishing the salts of this series from 
those of Xanthocobalt. In this salt, : 
0°4660 gr. gave 0°2128 gr. BaCrO, = 20°95 per cent CrO,. 
0°4659 gr. gave 119°5 c.c nitrogen at 9°75° C. and 753°5"™™=30°42# 
The formula, Co,(NH,),(NO,),CrO,, requires 20°97 per cent 
CrO, and 20°42 per cent of nitrogen, 
