M. Gay Lussac’s Reflections on Volcanoes. 285 
their lavas, on coming in contact with the air, and that by means 
of the heat, water and oxygen of the air, it is changed into a 
peroxide, which aggregates and assumes a crystalline form, on be- 
ing precipitated. 
On bringing chlorine in contact with an iron wire, at the tem- 
perature of about 400°, the iron becomes presently incandescent ; 
but not nearly so much so as with oxygen. The perchloride is 
very volatile; it crystallizes by cooling in small delicate spangles, 
which, in the air, are almost instantly dissolved by deliques- 
cence. It becomes so hot when brought into contact with water, 
that I should not be surprised if, when in a great mass, and 
with a corresponding quantity of water, it should become in- 
candescent. I make this observation to show* that if the sili- 
ciuill and aluminum were really in the state of a chloride in 
the bowels of the earth, they might produce a much higher 
temperature, on coming in contact with water, since their affi- 
nity for oxygen is much greater than that of iron. 
If it be disengaged from the sulphurous acid of volcanoes, as 
there can be no doubt it is, it is very difficult to form an opi- 
nion regarding its true origin. Whence does it obtain the oxy- 
gen necessary for its formation, unless it be the result of the de- 
composition of some sulphates by the action of heat, and of the 
affinity of their base for the other bodies ? This is what appears 
to me to be the most probable opinion ; for I cannot ima- 
gine, that sulphur, from its known properties* is an agent in 
producing volcanic fires. 
Klaproth and Vauquelin have conjectured that basalts 
might owe their colour to carbon ; but, to overthrow this conjec- 
ture, it is sufficient to remark, that, when a mineral which is 
fusible, and contains even less than 1 0 hundredth parts of oxide 
of iron, is heated strongly in a crucible* much of the iron is redu- 
ced, as Klaproth has shewn in the first volume of his Essays . 
Further, according to MM. Gueniveau and Berthier, there does 
not remain more than from 3 to 4 per cent of oxide of iron in 
the scoriae of furnaces. Now* as lavas contain much iron, and 
the basalts that have been analysed contain from 15 to 25 per 
cent, of it, it is not probable that carbon could remain together 
with so great a quantity of iron, without reducing it. 
Is it possible that metallic iron, if disengaged from the hydro- 
