pera 
On definite Proportions. 163 
united with 79:8 of oxide of iron, containing 24°47 of oxygen, 
while the acid contained 12°12; or, without any material error, 
half as mich as the oxide. We sce therefore that in the sub- 
sulphate of the oxide of iron the acid saturates six times as much 
of the base as in the neutral sulphate; for, according to the 
analysis of the neutral sulphate, whith I have already described, 
100 parts of sulphurie ‘acid saturate 65°5 of the oxide of iron, 
and 65:5 x 6 =393. But, according to the present analysis of 
the subsulphate, 100 parts of the acid are combined m it with 
395 of the oxide; and the difference is so small that it can only 
be attributed to an error of observation. 
I then collected a quantity of orange-yellow ochre, which had 
formed itself from a vitriolic solution in a vitriol work ; I washed 
it carefully, and dried it in the sun. When the water was ex- 
pelled over a spirit lamp, it had lost 21-7 per cent. By ignition 
it lost 15-9 per cent. more of sulphuric acid, and the remaining 
red mmmagnetical oxide amounted to 6274 per cent. According 
to this experiment, 100 parts of sulphuric acid combine, in the 
subsalt, with 392-52 of the oxide, and the yellow ochre is thus 
eonstituted: 
Sulphuric acid...... 15-9 100 
Oxide of iron.......) 62°4 392-52 
Watters deiia ts sag) DF 
The quantity of water contains 19-15, the oxide of iron 19-13, 
and the sulphuric acid 9°54 parts of oxygen. Consequently the 
base and the water contain equal quantities of oxygen, and the 
acid exactly half as much oxygen: so that, notwithstanding the 
great difference in their appearance, the yellow ochre and the 
brown red precipitate are exactly the same combination. I am 
sorry that the former analysis was made at a time when I had 
not begun to collect any observations respecting the water of 
crystallization. 
I was not alittle anxious-to know why this result differed so 
much from my former analysis of the same salt, and therefore 
prepared some more of the compound in the manner which I had 
then employed; dissolving some iron in diluted sulphuric acid, 
to which, for the sake of increasing the quantity of the oxide, I 
had added a little mitrie acid. When nothing more was dis- 
solved, J put, in order to expedite the separation of the subsalt, a 
piece of polished iron ‘ato the filtered solution, and exposed it, 
in an open vessel, to a temperature of 25° or 30° [77° to 86°] 
for several days. 1 thus obtained a considerable quantity of an 
ochre-coloured powder, possessing the characteristic property of 
‘the subsulphate of iron which I first analysed ; it was very little 
soluble in muriatie acid, and when dried scarcely at ‘all so, and 
was not altered by caustic potass. Whien | first dried this powe 
L der, 
