By H.N. WARREN, Research Analyst.
On the same principle that electro-dissolution is used for the estimation
of combined carbon in steel, etc., I have lately varied the experiment by
introducing, instead of steel, iron containing a certain percentage of
boron, and, having connected the respective boride with the positive pole
of a powerful battery, and to the negative a plate of platinum, using as a
solvent dilute sulphuric acid, I observed, after the lapse of about twelve
hours, the iron had entirely passed into solution, and a considerable
amount of brownish precipitate had collected at the bottom of the vessel,
intercepted by flakes of graphite and carbon; the precipitate, having been
collected on a filter paper, washed, and dried, on examination proved to be
amorphous boron, containing graphite and other impurities, which had become
chemically introduced during the preparation of the boron compound. The
boron was next introduced into a small clay crucible, and intensely heated
in a current of hydrogen gas, for the purpose of rendering it more dense
and destroying its pyrophoric properties, and was lastly introduced into a
combustion tubing, heated to bright redness, and a stream of dry carbonic
anhydride passed over it, in order to separate the carbon, finally pure
boron being obtained.
In like manner silicon-eisen, containing 9 per cent. of silicon, was
treated, but not giving so satisfactory a result. A small quantity only of
silicon separates in the uncombined form, the greater quantity separating
in the form of silica, SiO_{2}, the amorphous silicon so obtained
apparently being more prone to oxidation than the boron so obtained.
Ferrous sulphide was next similarly treated, and gave, after the lapse of a
few hours, a copious blackish precipitation of sulphur, and possessing
properties similar to the sulphur obtained by dissolving sulphides such as
cupric sulphide in dilute nitric acid, in all other respects resembling
common sulphur.
Phosphides of iron, zinc, etc., were next introduced, and gave, besides
carbon and other impurities, a residue containing a large percentage of
phosphorus, which differed from ordinary phosphorus with respect to its
insolubility in carbon disulphide, and which resembled the reaction in the
case with silicon-eisen rather than that of the boron compound, insomuch
that a large quantity of the phosphorus had passed into solution.
A rod of impure copper, containing arsenic, iron, zinc, and other
impurities, was next substituted, using hydrochloric acid as a solvent in
place of sulphuric acid. In the course of a day the copper had entirely
dissolved and precipitated itself on the negative electrode, the impurities
remaining in solution. The copper, after having been washed, dried, and
weighed, gave identical results with regard to percentage with a careful
gravimetric estimation. I have lately used this method, and obtained
excellent results with respect to the analysis of commercial copper,
especially in the estimation of small quantities of arsenic, thus enabling
the experimenter to perform his investigation on a much larger quantity
than when precipitation is resorted to, at the same time avoiding the
precipitated copper carrying down with it the arsenic. I have in this
manner detected arsenic in commercial copper when all other methods have
totally failed. I have also found the above method especially applicable
with respect to the analysis of brass.
With respect to ammoniacal dissolution, which I will briefly mention, a rod
composed of an alloy of copper and silver was experimented upon, the copper
becoming entirely dissolved and precipitating itself on the platinum
electrode, the whole of the silver remaining suspended to the positive
electrode in an aborescent form. Arsenide of zinc was similarly treated,
the arsenic becoming precipitated in like manner on the platinum electrode.
Various other alloys, being experimented upon, gave similar results.
I may also, in the last instance, mention that I have found the above
methods of electro-dissolution peculiarly adapted for the preparation of
unstable compounds such as stannic nitrate, potassic ferrate, ferric
acetate, which are decomposed on the application of heat, and in some
instances have succeeded by the following means of crystallizing the
resulting compound obtained.--_Chem. News_.
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