220 
Dr. Thomson on some of 
brown colour and was opaque. It was cautiously evaporated 
to dryness. An orange-coloured matter precipitated, which 
was sparingly edulcorated, because it was not quite insoluble 
in water. Of this orange powder I dissolved 10 grains in 
muriatic acid and threw down the peroxide of iron by 
ammonia. This precipitate after ignition weighed 4-102 
grains. It was strongly magnetic, and therefore the oxidum 
ferroso-ferricum of Berzelius —4-243 grains of peroxide. 
The residual liquid was neutralized by acetic acid and 
thrown down by acetate of lead. The chromate of lead ob- 
tained weighed after ignition 9-4 6 grains, equivalent to 3 
grains chromic acid. Thus, the constituents of the orange 
powder are, 
Chromic acid - - 3-000 or 6*5 or 1 atom 
Peroxide of iron - 4*243 or 9*193 or 2 atoms nearly. 
Water - 2- 757 or 5*973 or 5 atoms 
10-000 
Thus, the orange matter was a diperchromate of iron. 
I could not ascertain the weight of the diperchromate 
formed ; but if we suppose the whole peroxide of iron in the 
liquid to have been in the state of diperchromate, it is obvious 
that ( supposing it anhydrous ) it would amount to 
2*5 atoms chromic acid - 16-25 
5 atoms peroxide of iron - 25 
41*25 
Thus, only about of the chromic acid had combined with 
the peroxide of iron, the remainder must have still continued 
in the state of chromate of potash. 
