178 
MISCELLANY. 
On the mode of preparing and the most convenient form of the Hydrated 
Sesquioxide of Iron, to be used as an Antidote for Arsenious Acid, by MM. 
Bunsen and Berthold. — The best process to obtain this body in a pure 
state, consists in peroxiditing by means of nitric acid and heat, a solu- 
tion of pure sulphate of iron, precipitating the solution by ammonia, and 
washing the hydrated sesquioxide by decantation; it should not be forgot- 
ten that the solution should be completed before the acid is added, and the 
nitric acid added by small portions at a time; otherwise a considerable 
quantity of the neutral sulphate of the sesquioxide is separated under the 
form of a yellow powder, which is but slightly soluble. The chloride of 
iron is less suitable to the preparation of this substance, on account of the li- 
ability when precipitating by ammonia of obtaining a mixture with a large 
quantity of basic chloride of iron. Lest the precipitated sesquioxide should 
lose its hydratic water and thus diminish its feeble state of aggregation, 
it is not to be filtered, but having been allowed to settle for several days 
and superincumbent liquid poured off, it is to be preserved in closed 
vessels. 
However simple the process pointed out for the preparation of this an- 
tidote, there will not be wanting persons to propose modifications, and 
some of them so little suitable that we consider it to be useful to add 
some remarks on this subject. There is first of all a practice which 
should be rejected ; this is, to employ any other alkali than ammonia for 
the precipitation of the hydrated sesquioxide of iron : in fact, the least 
quantity of alkali retained in the precipitate, would give rise to the forma- 
tion of an arsenite which would completely prevent its precipitation by 
the sesquioxide; for this substance can completely overcome the affinity 
of the ammonia for the arsenious acid, but not that of potassa or soda for 
the same acid. It is necessary also to renounce the idea of being able, 
when employing a salt of the sesquioxide mixed with copper, to purify 
the precipitate obtained, from the copper, by means of an excess of ammo- 
nia. This purification is, as we know, always incomplete. But it is alto- 
gether inconceivable that any one depending upon some very inexact ex- 
periments upon animals, should recommend the preservation and use of 
the antidote in a dry state, since numerous experiments already made, 
and in agreement with our own, lead to the result, that the action of the 
sesquioxide of iron is of no effect, and that of the dry hydrate incomplete, 
as we would a priori conclude, since the dry hydrate never completely 
precipitates the arsenious acid in the cold. This recommendation to dry 
the product, appears to be dictated by the erroneous opinion that the hy- 
drate is altered and loses its efficacy by long preservation. We can 
disprove this with certainty, since we have found that a precipitated hy- 
drate of the sesquioxide, resulting from a carbonate of iron enclosed in a 
mass of travertin (carbonate of lime) which had been deposited under 
water, had preserved all its efficacy, and the condition of the mass of tra- 
