1 877.] in its Geological Relations. 473 
result in a renewed evolution of ammonia to the atmo- 
sphere. 
Under such circumstances occasionally the ammonia, in- 
stead of escaping freely into the air, meets with hydrochloric 
as in the depths of volcanoes, and combining with it is 
evolved as chloride of ammonium {sal-ammoniac) , which is 
condensed on meeting with the cooler external air. This 
mineral is often met with in large quantity, so much so, 
indeed, as to be of commercial value. Thus during the 
eruption of Vesuvius in 1794 great quantities of this salt 
were evolved, and it was collected by the peasantry ; and 
Hecla in 1845 yielded very profitable supplies of it. In the 
vapours of the Solfatara, at Puzzuoli, it is also met with, 
and it is found mixed with sulphur and other matters in the 
crater of Vulcano, where it is now being largely collected,* 
and in considerable quantity at Etna. Then the vol- 
canoes of Kutsche and Turfan, in Central Asia, afford such 
large supplies that it has been a very valuable article of 
commerce, t 
Prof. Judd is at a loss to explain the production of those 
large quantities of sal-ammoniac, unless on Daubeny’s sup- 
position that nitrogen under the influence of heat is 
unusually aCtive ; but the matter is readily accounted for 
thus : — The decomposition of nitrogenous organic matter at 
all times produces ammonia, but especially so under the in- 
fluence of heat (a familiar instance is the manufacture of 
coal-gas). That a sufficiency of such organic matter exists 
in the rocks through which these volcanoes have burst is 
undoubted, and the ammonia evolved combines with avidity 
with the hydrochloric acidf also given out in volcanic 
emanations. 
Quite lately a new mineral has been discovered incrusting 
the recent lavas both of Etna and Vesuvius. This is a 
nitride of iron named “ Sidevazote ” by its discoverer, 
Silvestri, || who considers it is due to the decomposition of 
ammonium chloride by heat in the presence of ferruginous 
lavas ; and although we may not quite accept his theory 
that the ammonium chloride is formed by the absorption of 
nitrogen direCt from the atmosphere by the lava, it is certain 
* J. W. Judd, “ On Volcanoes,” Geol. Mag., Dec. 2, vol. ii . , p. 113. 
t Bischof, op. cit., i., 212 — 213. 
i The formation of white fumes of ammonium chloride when a glass rod 
dipped in ammonia is brought near hydrochloric acid will occur to chemical 
readers. 
|| “ The Occurrence of Nitride of Iron amongst the Fumarole Products of 
Etna, and its Artificial Preparation.” Orazio Silvestri, Gazetta Chim. Ital., 
v., 301 — 307. Pogg. Ann., clvii., 165 — 172. 
