from other Metals. S9 
A similar change is produced by an increase of temperature. 
If we heat a solution exactly neutralized as above described, it 
speedily grows turbid, deposits its ferruginous contents in abun- 
dance, ani at the same lime acquires a very decided acid re- 
action. The acid so developed holds in solution a portion of 
oxide; but if the neutralization be performed afresh while hot, 
this separates entirely, and the liquid after filtration has no more 
action on gallic acid, ferroecyanate, or sulphocyanate of potash, 
than so much distilled water *. 
Tt is not my object in this paper to enter into any minute de- 
tail of the nature of the persalts of iron, a subject not nearly 
exhausted, and which want of leisure alone has prevented my 
entering upon, but merely to point out the practical application 
of this one of their properties, to an important object in analysis. 
The principle here developed furnishes a ready method of de- 
tecting the minutest quantities of other metals in union with 
iron, and therefore cannot but prove of important service in va- 
rious cases where this metal constitutes the chief ingredient in 
the substance examined, as in meteoric iron, the various natural 
oxides of this metal, &c. &c. I will exemplify this in one or two 
instances. 
35-00 grains of meteoric iron (furnished me by the kindness of 
Dr. Wollaston) were dissolved in dilute nitro-sulphuric acid, 
leaving behind a minute quantity of a brilliant black powder, 
which however dissolved by digestion in nitro-muriatic acid, and 
appeared only to contain an excess of nickel. The solutions were 
mixed, and being neutralized at a boiling temperature by car- 
bonate of ammonia, and the iron separated, a green solution re-~ 
mained. Into this when boiling, a drop of persulphate of iron 
being let fall, was immediately precipitated in the state of sub- 
sulphate, which being separated, the solution was boiled with 
excess of caustic potash till all smell of ammonia disappeared. 
Oxide of nickel separated, which collected and strongly ignited, 
weighed 4°65 grains, or 12°92 on the hundred, which (taking 
* It was in 1815, in the analysis of a specimen of the gold ore of Bake- 
banya, given me for that purpose by Dr. Clarke, that I first remarked the 
separation of oxide of iron from a clear neutral solution by mere elevation 
of temperature, and attributed it to the presence of an oxycarbonate capable 
of subsisting in a low temperature, but decomposed by heat. That this is 
not the true explanation is already shown, and I have considerable doubt 
of the existence of a percarbonate of iron at any temperature. 
The most elegant mode of exhibiting the experiment is perhaps the fol- 
lowing: Waving rendered a solution of proto-sulphate of iron rigorously 
neutral, by agitation with carbonate of lime’ and filtration, dissolve in it a 
small quantity of chlorate of potash (a salt perfectly neutral). The solu- 
tion when raised to ebullition is peroxidized, a quantity of sub-sulphate pre- 
cipitates, and the supernatant liquid is found decidedly, and even strongly 
acid. 
Vol, 59, No, 286, Fel, 1822, M the 
