the compounds of chromium. 1 77 
Various repetitions of this experiment were made, but I was 
never able to obtain a solution of protosulphate of iron abso- 
lutely free from all admixture of peroxide. There was 
therefore always a loss. When the preceding quantities 
were employed, the smallest loss amounted to 0-07 grain, 
and the greatest to o - 2 grain ; but notwithstanding this loss, 
never exceeding 1 per cent, and sometimes less than a half 
per cent, the experiment is conclusive, that 5 is the atomic 
weight of green oxide of chromium ; and that 65 chromic 
acid become green oxide when deprived of 1-5 oxygen. 
It is obvious that the 16-81 grains of black matter obtained 
were composed of 
Peroxide of iron - - 13-63 or 20-404 
Protoxide of chromium - S' 34 or 5 
1697 
That is to say, it is a compound of 4 atoms peroxide of iron, 
and 1 atom green oxide of chromium. On subjecting a por- 
tion of it to analysis, I obtained 
Peroxide of iron - - 8-77 or 21-286 
Green oxide - - - 2-06 or 5 
Now, if we subtract from the 3-34 of green oxide the 0-16 
of loss, it is obvious that the true composition of the powder 
will be Peroxide of iron - 21-11 
Green oxide of chrome - - 5 
The analysis therefore, notwithstanding the smallness of 
the scale, comes near enough the truth to show that it had 
been conducted with care. 
Having thus established the true atomic weight of chro- 
mium, and protoxide of chromium, the experiments which 
mdcccxxvii. A a 
