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 lo 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*46 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*i93 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 i of the chromic acid had combined witii 
the peroxide of iron, the remainder must have still continued 
in the state of chromate of potash. 
