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NOTE UPON SESQUINITRATE OF IRON. 
ART. XXII.— NOTE UPON SESQUINITRATE OF IRON. 
By Augustine Duhamel. 
A formula for the preparation of this substance in solu- 
tion is given in the last edition of the U. S. Dispensatory. 
Prepared, as there indicated, it furnishes a transparent 
deep red solution Agreeable to the recommendation of 
Mr. Kerr, by whom the formula is given, and with the 
view to prevent decomposition some hydrochloric acid is 
added, in quantity so small as not to affect its medicinal ac- 
tion, but sufficient, as he supposed, to preserve its charac- 
ter as a sesquinitrate of the sesquioxide of iron. This ob- 
ject, however, is not accomplished. Not only myself, but 
others have invariably found that, after a few weeks stand- 
ing, the solution becomes wholly turbid and incapable of 
passing clear by nitration ; the further action of time occa- 
sions a spontaneous deposit of a floculent ochrey oxide, 
while the clear fluid stratum is changed to a light reddish 
yellow colour, and is less dense than the original solution. 
In accounting for this change, the first question which 
presents itself is relative to the true constitution of the pre- 
paration. Is it a sesqui-nitrate of sesqui-oxide of iron in 
solution? According to Thenard, " always in treating iron 
by nitric acid, this metal passes to at least the state of oxi- 
dation represented thus: Fe + Fe 2 O 3 ." This formula 
is that of the black or magnetic oxide of iron, and the ex- 
istence of the iron in this state is proven by adding am- 
monia, which throws down the black oxide in a hydrated 
form. Hence the change which occurs in the medicinal 
solution is owing to the peroxidation of the equivalent of 
protoxide of iron, and the consequent precipitation of at 
least a portion of it in the form of the ochrey sediment. 
The change may be thus explained: 6 (Fe 0, Fe 2 O 3 -f 
4 NO*) + O 3 == S (Fe 2 O 3 + 3 NO 5 ) + (Fe 2 O 3 .) 
It follows from this, that every six equivalents of the 
