Vulcano appears to have been frequently in a state of violent eruption during the past 2,000 years--the last great outburst having taken place in 1786. In 1873 the activity in the crater of Vulcano suddenly became more pronounced in character, and the workmen hastened to escape from the dangerous spot, but, before they could do so, several of them were severely injured by the explosions. After this outburst, which did not prove to be of very violent character, the quantity of gases issuing from the fissures in the crater was for a time much greater than before, and the productiveness of these great natural chemical works was proportionately increased: but eventually the action died out almost entirely. The chief products of Vulcano which are of commercial value, are sal-ammoniac, sulphur, and boracic acid. At one time it was even contemplated that great leaden chambers should be erected over the principal fissures at the bottom of the crater of Vulcano, in which chambers the volatile materials might be condensed and collected. The change in the condition of the volcano has unfortunately prevented the carrying out of this bold project. Besides the volatile substances which issue from volcanic vents, mingling with the atmosphere or condensing upon their sides, there are also many solid materials ejected, and these may accumulate around the orifices, till they build up mountains of vast dimensions, like Etna, Teneriffe, and Chimborazo. Some of these solid materials are evidently fragments of the rock-masses, through which the volcanic fissure has been rent; these fragments have been carried upwards by the force of the steam-blast and scattered over the sides of the volcano. But the principal portion of the solid materials ejected from volcanic orifices consists of matter which has been extruded from sources far beneath the surface, in a highly-heated and fluid or semi-fluid condition. [Sidenote: EJECTED ROCK-FRAGMENTS.]