VARIOUS STATES OF ITS NITRATE.
533
fection, with a rich colour, pours fresh nitric acid on it, and distils it
to dryneſs, three times.
I faid that, in the ſtate of a nitrate, this compound exhibited certain
uniform differences in the form and structure of its crystals. When
the solution has been made without the affistance of heat, and the
mixture kept close during the process, and if it be allowed to evapo
rate ſpontaneoufly, the crystals are thin square plates, whose four sides
are formed into an edge, like that of a stone-cutter's chizel, and hav
ing the four angles cut off; that is, the crystals are formed of two te
trahedral pyramids, joined at their base, and having the angles cut off.
(See Romé de l'Isle, No. 38. VI. 11.)
But if the evaporation has been promoted by considerable heat, the
crystals are flat-pointed spiculæ, having the flat side elegantly striated
in an oblique direction, like a sword blade which has been ground by
holding it very obliquely on a rough stone. If the solution has been
effected by heat, the crystals are also flat spiculae, like lancets; but the
striæe are now parallel to their lengths. This pointed form of all the
crystals has been much insisted on by the mechanical chemists, in their
attempts to account for the corroding powers of the mercurial nitrate,
but, unluckily, the moſt eorrosive are the crystals in flat plates.
Mr. Fourcroy has treated this ſubject with the ſame diſtinctneſs and
perspicuity as the solution in sulphuric acid; and his analysis of the
different states of the nitrate seems to me very judicious and instruc
tive.
The muriatic acid, in its ordinary ſtate, has little power to act on
mercury in its metallic form. This is a consequence of the weak power,
or rather want of power, in this acid to oxydate the metals; and they
muſt be oxydated in some degree, in order to form compounds with
acids. But the muriatic acid oxygenated by manganese, readily unites
with metals in general, and forms a faline compound, the oxygen be
ing in this case supplied to the metal by the acid. We can therefore
easily obtain a compound of mercury and the muriatic acid, by employ¬