ON PERCHLORIDE OF IRON. 
169 
M. Mohr has recently proposed to prepare the perchlo- 
ride of iron by dissolving haematite by digestion in com- 
mercial hydrochloric acid, and boiling the mixture towards 
the end of the operation. The liquor is allowed to become 
clear, is then evaporated to the consistence of a syrup, and 
afterwards exposed in a covered vessel, in a cold place, 
such as a cellar, where after a few days it begins to crys- 
tallize, and continues to do so for several weeks. The mother- 
water is decanted, and the crystals preserved. 
M. Mohr analysed the chloride prepared in this way, 
and found it to contain twelve atoms of water. He has 
therefore assigned to it the formula Fe 2 Cl 3 + 12 H 0. 
M. Fristche, who undertook a fresh investigation to de- 
termine the proportion of water contained in Mohr's chlo- 
ride, found that the analysis of this chloride (and the same 
is also true of those prepared according to the processes of 
Orfila, Thenard, and Berzelius) affords very variable re- 
sults with reference to the proportion of water, so that it is 
impossible to say whether it contains 10, 11, or 12 atoms 
of water. With 10 atoms it should contain 35.92 percent., 
with 11, 38.15, and with 12, 40.22. 
According to the same chemist, if the p reading chloride 
be left under a bell-glass with sulphuric acid, the crystals 
are again reduced to the state of a thick liquid, from which 
fresh crystals are formed, containing from 21 to 23 per cent, 
of water. If they contained 5 atoms of water, there would 
be 21.9 per cent. These same crystals may also be ob- 
tained, according to M. Fristche, by fusing the chloride 
with 10, 11, or 12 atoms of water, evaporating so that a 
drop will solidify on cooling, and adding a few drops of 
concentrated hydrochloric acid before putting it to cool. 
M. Fristche has been led by his researches to admit the 
existence of two hydrates of perchloride of iron perfectly 
crystallizable, between which there is no crystallizable 
combination. 
As will be seen, many processes have been given for the 
