202 
Dr. Thomson on some of 
1 atom muriate of chromium | ^ 1 9-625 
* oxide 5'000 j 
i * 1 
aci 13 y g 
oxide 5 3 
3 atoms water - - - _ _ 3-375 
31-000 
And the matter when allowed to absorb as much water as 
possible contains 27 atoms of that liquid. 
It is not easy to form a conception of the way in which the 
reduction of the chromic acid to green oxide takes place. 
The heat employed was never sufficient to drive off the 
oxygen. Had the chlorine heeTi converted into muriatic acid, 
the oxide of chromium should have been acidified, at least in 
part. Hence I am disposed to think that it is not muriatic 
acid which the black matter contains, but chlorine. A simi¬ 
lar disorganisement takes place, if chromic acid itself be left 
for some time on the sand bath. Hence, I am disposed to 
ascribe the reduction to the tendency which chromic acid has 
to unite with protoxide of chromium. We may conceive that 
the elasticity communicated to the oxygen of the acid by the 
heat, together with the affinity of chromic acid for protoxide, 
may occasion the reduction of a portion of the acid, and cause 
the oxide formed to unite with the acids in the liquid. 
V. Salts of chromium. 
The green oxide of chromium combines with the different 
acids and forms a genus of salts, not one of which, so far as 
I know, has been described by chemists. I shall therefore 
embrace the present opportunity to give a short account of 
them. 
