Volcanoes are natural laboratories in which chemical processes are conducted on a grand scale. As wo cannot descend into them to discover their mode of operation, or the materials on which they operate, we can only judge of them by their products. The nature of their solid products, lava, scoria, lapilli, and ashes, have been carefully studied, but their gaseous products are less easily subjected to examination, and are less accurately known. The deficiency of our information on the latter seems to have induced the Paris Academy of Sciences to send two of their men of science, Messr3. St. Clair Deville and Lcblanc, to Italy, on a special mission to examine the gases which issue from the volcanoes of that country. They were supplied with peculiar apparatus, made for the purpose of collecting and preserving the gases, and partly for examining them on the spot. The memoir containing the result of their investigations ha been made the subjoct of a report. They state that they were onabled by their apparatus to collect gases not only at the orifice of the volcano, but at great depths in tht vent; in the latter case by slender tubes, which were rapidly closed by the blow-pipe. The gases they brought away and analysed in Paris were from Vesuvius, the Phlegrean Fields, one of the Lipari Isles (Vulcano), and Etna. Mixed with the gaseous products they found much heated air, more or less altered by the addition of gas or vapors, or the absorption of oxygen, which lod them to believe that common air penetrate* into the vent of the volcano by a fissure, k exhaled by it and escapes heated. Sometimes carbonic acid constitutes only 9 or 10 per cent of the aeriform discharge, as in the fumeroles of Vesuvius; sometimes it amounts to 67-74 per e'ent, as in the Grotto del Cane, and is found pure in the emanations of the Lake of Agnana. Sulphurous (tcid, at times scarcely appreciable, rises to G, , or 8 per cent in the emanations of the Sol- tara, and to 35 per cent hi the fumeroles or gas vents of tho Island of Vulcnao.
This article was originally published with the title "Volcanic Emanations" in Scientific American 13, 26, 201 (March 1858)