PREPARATION OP THE PERCHLORIDE OP IRON. 145 
perchloride of iron are very numerous ; but it may be said 
that neither admits of the perchloride being obtained of a 
constant composition, in a short time, entirely soluble and 
capable of long preservation. The principal cause of the 
easy alteration of the chloride of iron prepared by the pro- 
cesses described, appears to be the large quantity of water 
which the preparation retains ; for instance, that of M. Beral, 
which contains least, affords, shortly after its preparation, 
a perceptible deposit of oxychloride when dissolved in 
water. 
Induced by M. Soubeiran to find out a practical process 
which would allow of obtaining in a short time a perchlo- 
ride of iron completely soluble, and of a constant composi- 
tion, I believe I have succeeded by submitting the solution 
of sesquioxide of iron in hydrochloric acid to the two fol- 
lowing conditions of evaporation : — 1st, evaporation at 
a temperature not exceeding 212°, and 2nd, evaporation 
in pefectly dry air. 
After several experiments I stopped at the following 
process : — Pulverized haematite is introduced into a stop- 
pered flask, and a quantity of pure concentrated hydrochlo- 
ric acid poured over it; there should be an excess of haema- 
tite ; it is then agitated. The two bodies soon react on 
each other, forming water and perchloride of iron, with 
disengagement of heat ; when the first action is passed over, 
the flask is placed near the fire and shaken frequently ; 
after several hours contact it is allowed to subside, and is 
filtered. The filtered liquid is received in a porcelain cap- 
sule, which is placed either on some sand heated by steam 
or on the head of an alembic, taking care to interpose a 
piece of flannel between the alembic and the capsule, and to 
maintain this in its position by means of a piece of string. The 
apparatus should be so arranged that the steam is conveyed 
by a long tube into a vessel full of cold water ; for it is es- 
sential to the success of the operation that no aqueous va- 
por should circulate around the capsule ; since, when the 
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