£2 ALTERATION BY THE HYDRATED OXIDE OF IRON. 
ART. XX.— ALTERATION EXPERIENCED BY THE HYDRATED 
OXIDE OF IRON UNDERWATER. 
By Dr. G. C. Wittstein. 
A solution of sulphate or hydrochlorate of iron yields 
with ammonia a very voluminous flushy brownish-red pre- 
cipitate of Fe 2 3 4-3HO, easily soluble in cold acetic acid. 
These facts are well known ; but it is scarcely, if at all, 
known that a similar precipitate, which has been allowed 
to remain some time under water, and, consequently, which 
has never been dried, loses entirely, or in great measure, 
its power of solution in acetic acid, just as though it had 
been dried. Other organic acids, moreover, which, under 
ordinary circumstances, dissolve undried oxide of iron with 
great facility, as, for example, tartaric and citric acids, take 
up a much less quantity of oxide thus prepared. I have 
already remarked in this journal, vol. 92, sec. 290, the cir- 
cumstance alluded to, having found that in the preparation 
of citrate of oxide of iron the freshly prepared oxide was 
necessary to the effect. Since that period I have investiga- 
ted the cause of this peculiar behaviour, and with a fortu- 
nate result. 
If a portion of the precipitate recently thrown down be 
washed, and then examined microscopically, no trace of 
crystalline structure, properly so called, is observable, the 
particles consisting merely of little amorphous bodies. If, 
however, a portion of the oxide which has been allowed to 
remain under water be examined, it is found to be crystal- 
line throughout. The little crystals are of a dark yellow 
colour, and moderately transparent. How long a period of 
aqueous submersion is necessary to effect this crystalline 
change I am unable to say — my crystalline deposit, which 
I microscopically examined, was more than two years old; 
it is, however, exceedingly probable that the peculiar change 
