_Carbonate of Iron._
In a former Pharmacopœia of London, a sub-carbonate of iron was
prepared, under the name of _ferri-rubigo_ (rust of iron,) by exposing
iron-filings to the action of air and water; and although the Colleges
of Edinburgh and Dublin still retain this mode of preparation, yet they
admit at the same time of another which, like the _sub-carbonate_ of the
present London Pharmacopœia, is produced by precipitation. QUALITIES.
_Form_, a chocolate brown powder. _Odour_, none. _Taste_, slightly
styptic. CHEMICAL COMPOSITION. Mr. Phillips has shewn that this
precipitate is liable to vary according to the temperature at which it
is prepared, as well as from other differences of manipulation; it
generally consists of mixtures of peroxide, and proto-carbonate of iron,
in the proportion of four parts of the latter, and six of the former. By
referring to the _Medicinal Dynameter_ the practitioner may find the
quantity of those ingredients in any given weight of the preparation,
and compare its strength with the other chalybeate medicines.
SOLUBILITY. It is insoluble in water, but acids dissolve it with
effervescence. _Forms of Exhibition._ In powder or pills, combined with
aromatics. DOSE, gr. v to xxx. (_Form. 38._) It has lately been brought
into particular notice by the publication of Mr. Hutchinson of
Southwell, who states that in doses of half a drachm to a drachm, two or
three times a day, it has proved in his hands a most efficacious remedy
in the cure of _Tic doloureux_. Mr. Hutchinson is well known to the
profession as a judicious and inquiring practitioner, and we are well
satisfied that he would not recommend any remedy to the attention of his
brethren, without a well grounded assurance of its efficacy; at the same
time it must be remembered that this disease is very frequently the
consequence of an irritation in some nerve, by the mechanical operation
of osseous spiculæ; in such cases we cannot expect the sub-carbonate of
Iron to afford relief. A noble Marquis who lost his leg at Waterloo,
suffered excruciating pains in his face, in consequence of exfoliation
in the stump, which were relieved as soon as the local irritation
subsided; and a late lamented physician appears to have owed his severe
sufferings to the irritation produced on the brain by a bony
excrescence. I have little doubt if cases of _Tic doloureux_ were more
carefully examined, they would be frequently found to derive their
origin from a similar source. If it were necessary I could add several
of such instances to those already enumerated.[506]