ON LIQUOR FRRRI NITRATTS. 
313 
on the proportion of proto-nitrate existing in the preparation when 
filtered from the excess of iron, it being greater as the amount of 
the proto-salt is greater. If the solution is filtered off from the ex- 
cess of iron as soon as the reaction has ceased to be active, it will 
contain much less of the proto-nitrate, than if the contact con- 
tinues for a length of time (12 hours). The reason of this appears 
to be, that a portion of iron is oxidized, and dissolved at the ex- 
pense of the acid of the ter-sesquinitrate, reducing a part of that 
salt to the condition of an insoluble subnitrate, which salt is subse- 
quently increased in quantity at the expense of the proto-nitrate, by 
its gradual conversion into ter-sesqui-nitrate, which remains in so- 
lution, and sub-sesquinitrate which precipitates. 
If, however, instead of proceeding according to the officinal di- 
rections, the nitric acid is diluted to the sp. gr. 1.15 and the iron, 
in the form of iron wire, as card teeth, be gradually added, so that 
the active reaction nearly ceases after each addition, till it is satura- 
ted, and then filtered, a solution is obtained containing a much smal- 
ler proportion of the proto-nitrate. If now this is heated gently, and 
nitric acid is slowly dropped in, stirring after each addition until 
the solution yields a reddish brown precipitate with ammonia, the 
solution is entirely free from the proto-nitrate., and has a much 
lighter color. The slight excess of nitric acid that exists in 
the solution thus prepared, is, therapeutically considered,probably an 
advantage. Dr. Bache, (U. S. Dispensary, 9th edit,, page 1008,) 
suggests that " a permanent solution might be prepared by dissolv- 
ing moist hydrated sesqui-oxide of iron in nitric acid to saturation." 
This suggestion, however correct in theory, is not easily practised, 
because, after sufficient of the oxide is dissolved to form a true ter- 
nitrate, the dissolution of the oxide continues until a large portion 
of sub-sesqui-nitrate is formed, and unless the exact proportions 
of acid and base are used, the operator has no clue to guide him 
in the process. 
The following modification of the officinal direction is offered 
as yielding a true sesqui-salt in solution, and of equal strength 
with that of the Pharmacopoeia : 
Take of Iron Wire (card teeth) cut in pieces, an ounce. 
Nitric Acid (sp. gr. 1.42) three fluid ounces ; 
Distilled Water, a sufficient quantity. 
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