184 Dr. Thomson on some of 
a red heat: it was then brought into fusion, and kept in that 
state for about 20 minutes. The fuzed mass on cooling had 
a fine yellow colour. Being digested in water a dirty brown 
matter remained, weighing when dried on the filter i‘89 
grain. When ignited it became green, but did not glow, and 
the weight was reduced to 1*19 grain. Thus 11*8 grains of 
green oxide were converted into chromic acid. The potash 
solution treated as before gave 49'21 grains of chromate of 
lead, equivalent to 15-603 grains of chromic acid. Thus, 
11-8 grains of green oxide became 15*603 chromic acid. 
According to this experiment, we have chromic acid com¬ 
posed of Protoxide ii*8 or 4*654 or 4*915 
Oxygen 3*803 or 1*5 or 1*585 
15*603 6*154 6-5 
These experiments all deviate a good deal from the truth. 
The mean of the three gives us the constituents of chromic 
acid, as follows: 
Protoxide - - 4*957 
Oxygen - - 1*543 
This gives us 4*957 for the atomic weight of green oxide. 
The deviation from the truth does not amount to 1 per cent. 
I expected by this mode of experimenting to have obtained 
much more satisfactory results. 
3. A quantity of liquid chromic acid was evaporated to 
dryness, forming, as usual, a very deliquescent red mass, 
which I found by analysis to consist of 
Pure anhydrous chromic acid - 88*97 
Protoxide of chromium - - 4-30 
Water - _ _ - _ 6*73 
7 00*00 
