FUMAROLE, a vent from which volcanic vapours issue, named indirectly from Lat. fumariolum, a smoke-hole. The vapours from fumaroles were studied first by R. W. Bunsen in Iceland, and afterwards by H. Sainte-Claire Deville and other chemists and geologists in France, who examined the vapours from Santorin, Etna, etc. The hottest vapours issue from dry fumaroles, at temperatures of at least 500° C, and consist chiefly of anhydrous chlorides, notably sodium chloride. The acid fumaroles yield vapours of lower temperature (300° to 400°) con taining much water vapour, with hydrogen chloride and sulphur dioxide. The alkaline fumaroles are still cooler, though above and evolve ammonium chloride with other vapours. Cold fumaroles, below oo°, discharge principally aqueous vapour, with carbon dioxide, and perhaps hydrogen sulphide. The fumaroles of Mont Pelee in Martinique during the eruption of 1902 were examined by A. Lacroix, and the vapours analysed by H. Moissan, who found that they consisted chiefly of water vapour, with hydrogen chloride, sulphur, carbon dioxide, carbon monoxide, methane, hydrogen, nitrogen, oxygen and argon, issuing at a temperature of about 400°. (See VOLCANO. )