per cent.

During the eruption of Etna in 1869 Von Waltershausen noticed on some of
the lava blocks which were still hot and smoking, silver-coloured
particles, which rapidly underwent change. An insufficient quantity for
analysis was collected, but during the eruption of 1874, Silvestri found
a quantity of the substance and analysed it. (_Poggendorff's Annalen_,
CLVII. 165, 1876.) It possesses a specific gravity of 3.147, and shows a
metallic lustre similar to that of steel. On analysis it was found to
consist of:--

Iron 90.86
Nitrogen 9.14
------
100.00

which corresponds with the formula Fe{5}N{2},--a formula assigned by
Fremy to Nitride of iron. It has been named _Siderazote_. This new
mineral species appears to be formed by the action of hydrochloric acid,
and of ammonia on red-hot lava containing a large percentage of iron. It
was formed artificially by exposing fragments of lava alternately to the
action of hydrochloric acid and ammonia in a red-hot tube. At a high
temperature Siderazote undergoes decomposition, nitrogen being evolved.
In contact with steam at a red heat it forms magnetite and ammonia.

_The Mineral Constitution and Microscopic Characters of some of the
Lavas of Etna._

By Frank Rutley, F.R.G.S., of H.M. GEOLOGICAL SURVEY.

A cursory examination of the series of specimens collected by Mr.
Rodwell, seemed to show that all the lavas of Etna, irrespective of
their differences in age, exhibit a remarkable similarity in
mineralogical constitution. Occasionally, however, there appears to have
been a little difference in their respective viscidity at the time of
the eruption, the crystals in some of them lying in all directions,
while in others there appears to be a more or less definite arrangement
of the felspar crystals, as seen in the lava of A.D. 1689.

Although the specimens which I have examined microscopically do not
appear to differ in the nature of their constituents, yet in some of
them certain minerals fluctuate in quantity, some containing a
comparatively large amount of olivine and well-developed crystals of
augite, while, in others, these minerals, although one or other is
always present, are but poorly represented by minute and
sparsely-disseminated grains. It seems probable that all the Etna lavas
contain traces of a vitreous residuum, since, when sections are
examined under the microscope, a more or less general darkn