ALTERATION BY THE HYDRATED OXIDE OF IRON. 63 
alluded to occurs much sooner, because I remember that a 
portion of oxide which had been allowed to remain half a 
year under water, presented an alteration of external ap- 
pearance, having become more compact. 
Not only does this alteration of microscopic structure 
take place amongst the particles, but the more insoluble 
compound only contains half the original quantity of water, 
itsformula being 2Fe 2 3 -f3HO. Consequently the diminished 
solubility of the altered oxide depends on two causes — its 
altered constitution in regard to water of combination, and 
its altered microscopic condition. 
Perhaps it is not an indifferent matter whether as an 
antidote for arsenious acid the hydrated oxide have been 
long standing under water or the contrary ; at any rate, of 
two preparations of this oxide the more recent should have 
the preference ; and it would be prudent to recommend 
that the store of hydrated oxide should be renewed every 
half year. The old preparation having given place to the 
new should not be thrown away, but redissolved in hydro- 
chloric acid, and again precipitated by ammonia, when its 
original properties are renewed. — Chemist, from Buchner's 
Repertorium. 
Note. — The reader is referred to page 29, vol. 14th of this Journal. 
In the article referred, to the results obtained now by Dr. Wittstein were 
then arrived at, and under similar circumstances. The summary of 
that paper says — " That hydrated peroxide of iron, even when kept 
under water, gradually decreases in its power of neutralizing arsenious 
acid," and "that this decrease in power is probably due to a change 
in the relative proportion of the oxide, and the water chemically combined with 
it, as well as to an alteration in its state of aggregation.''' 1 The micro- 
scopic observation of Dr. Wittstein in reference to this change is 
corroborative of that statement. W. P., Jr. 
