I 
ON HYDRATED PEROXIDE OP IRON. 7 
simple fact that the dry hydrate does not ever precipitate, 
wholly, in the cold arsenious acid, should have previously 
apprised every one." 
" The recommendation to dry the product seems to arise from 
the erroneous opinion, that the hydrate undergoes a change, 
and loses its efficacy by long preservation. We have it in 
our power to refute this view of it, since we have found that 
a precipated hydrated sesquioxide obtained from carbonate of 
iron, enclosed in the cavity of a mass of travertin (sediment- 
ary carbonate of iron,) removed from under water, had pre- 
served its efficacy, notwithstanding the geological conditions 
of the mass of travertin, demonstrated that many ages, at 
least, ought to have rolled over since its deposition took 
place. This precipitate of the sesquioxide owes its action al- 
together to its gelatinous hydrated state, which was perfectly 
preserved under the bed of water, beneath which it was depo- 
sited. It would, however, be a great error to attribute the 
same efficacy to dry ochre, to bog iron ore, (fer oxide des 
marais,) or to the argillaceous oxide of iron ; these substances, 
from their mode of aggregation, are equally inert, with the 
deposit produced in the water, in which smiths cool their 
iron, which is not a hydrated sesquioxide, but a deposit of the 
mixed oxides. This last substance is not even inert, on ac- 
count of its sharp corners, which would prove a source of 
dire consequences." 
There is an apparent difference of opinion between the 
value of the peroxide, as employed by Dr. Von Specz, 
and the authors here quoted, but so far as regards the 
necessity of a recent precipitate, they concur, and fully 
sustain the opinions which I have advocated. Dr. Von 
Specz, indeed, requires that the oxide shall be administered 
in the form of an emulsion, in which, if properly prepared, 
it must be completely divided and thoroughly diffused. 
The conclusions, then, which I consider established, both 
by the evidence here offered, and the absence of evidence to 
the contrary, are, 
