187 
the compounds of chromium. 
assumed the green colour of protoxide of chromium. From 
these trials I was led to suspect, that this supposed oxide 
might be nothing else than common green oxide of chromium 
combined with a certain determinate quantity of chromic acid. 
The following experiments were made with a view of deter- 
mining how far this suspicion was well founded. 
8 grains of brown oxide of chromium were heated on the 
sand bath till they ceased to lose weight. The brown colour 
was not altered, but the weight was reduced to 6-8 grains. 
When this matter was exposed to a red heat it did not glow, 
but became black, and similar to brown oxide after it has 
been once or twice washed in ammonia. The weight was 
reduced to 6-24 grains. 
Brown oxide, when digested in nitric acid, was dissolved. 
The solution had a green colour, a very sweet taste, and 
possessed the usual characters of nitrate of chromium. It 
dissolved likewise in muriatic acid. The solution was green- 
coloured, sweet tasted, and precisely similar to common 
muriate of chromium. 
These facts seemed to show decisively, that this supposed 
brown oxide does not combine with acids ; and that when 
treated either with acids or alkalies, it is resolved into com- 
mon green oxide and chromic acid. 
To determine the quantity of chromic acid in brown oxide 
of chromium, the following experiments were made : 6 - 81 
grains of brown oxide, previously exposed to an incipient red 
heat, were put into a green glass tube, through which a 
current of dry hydrogen gas was made to pass, while the 
oxide was kept at a red heat by means of a spirit lamp. No 
combustion took place ; but a little water was formed, and 
