the compounds of chromium. 
207 
blues. When evaporated to dryness, there remains a dark 
matter, having a green colour, so intense, that it appears 
black. It is tasteless, does not affect vegetable blues, and is 
easily reduced to a fine powder. It is not altered by expo- 
sure to the air, and seems at first to be insoluble in water ; 
but when we pour water over it, and apply heat, the sulphate 
gradually dissolves in the liquid, and the solution has the 
same colour and the same sweet acidulous taste as at first. 
To determine the composition of this salt, 345 grains of 
the hydrated oxide, dried in the open air (containing 55 grains 
of oxide), were digested in a flask with a quantity of sul- 
phuric acid of commerce, containing just 55 grains of real 
acid. The solution was complete ; and the liquid being 
evaporated to dryness, the dry tasteless residue weighed 
151*4 grains. Now, as the acid and oxide together amounted 
to 110 grains, it is clear that the water in the salt must 
amount to 41-4 grains. Thus the constituents of sulphate of 
chromium are 
Sulphuric acid - - 55 or 1 atom. 
Green oxide of chrome 55 or 1 atom. 
Water - 41*4 or 3^ atoms. 
We may therefore without sensible error consider sul- 
phate of chromium as composed of 
Twenty grains of the dry salt being heated to incipient 
1514 
1 atom sulphuric acid 
1 atom green oxide 
3 atoms water 
5 
5 
3' 31 5 
13*375 
