the compounds of chromium. 219 
grains ; but when it had been exposed to a red heat the 
weight was reduced to 23-368 grains. It had a brown colour 
with a slight shade of red, was tasteless and insoluble in 
water, and was not in the least attracted by the magnet. 
10 grains of this matter, as it had been dried on the filter, 
were dissolved in muriatic acid and precipitated by ammonia. 
The peroxide of iron thus collected being edulcorated, dried 
and ignited, weighed 6-14 grains. The residual liquid was 
saturated with acetic acid and precipitated at a boiling tem- 
perature by acetate of lead. The chromate of lead obtained 
weighed after ignition 4' 82 grains, equivalent to 1-53 grain of 
chromic acid. From a preceding experiment, it is plain that 
the 10 grains of matter analyzed contained 2 -33 grains of 
water ; so that the constituents were, 
Chromic acid - - 1-53 or 6-5 or 1 atom. 
Peroxide of iron - 6-14 or 26-08 or 5 atoms. 
Water - 2*33 or 9-87 or 9 atoms nearly. 
10-00 
We see that the salt is a compound of 1 atom chromic acid 
and 5 atoms peroxide of iron. Or it is a pentachromate of 
iron. 
1 atom chromic acid - - 6-5 
5 atoms peroxide of iron - 25 
3i*5 
It would appear from this, that when per-muriate of iron 
and chromate of potash are mixed in equal atomic proportions, 
one-half of the peroxide of iron falls united to one-tenth of 
the chromic acid, forming a pentachromate of iron. 
The liquid which passed through the filter had a dark 
