J. W. Judcl — On Volcanos. 113 



the action of sulphurous acid and sulphuretted hydrogen on one 

 another. The production of the large quantities of chloride of 

 ammonium can scarcely be explained, however, unless we admit with 

 Daubeny that nitrogen, under conditions of high temperatures and 

 pressures, exhibits a chemical activity, very different indeed from its 

 inert character under ordinary circumstances. 



The quantity of volatile matter issuing from the fumaroles of 

 Vulcano varies from day to day, and new fissures are being con- 

 tinually opened, while old ones become closed. Signor Pinconi 

 assured me that, after the recent eruption, the fumaroles discharged 

 with enormously augmented violence, and that they produced, at the 

 time of my visit, at least four times the quantity of salts deposited 

 before the eruption. Two condensing chambers had just been 

 erected over the largest fumarole for the artificial condensation of the 

 vapours, but sufficient time had not elapsed to test the success of this 

 method of collection. At present, the crusts composed of boracic- 

 acid, sulphur, and sal-ammoniac are dug up round the fumaroles and 

 conveyed to the outside of the crater by an excellent road carried 

 over a viaduct. The sulphate of alumina, which is also largely 

 collected, is produced by the action of the acid vapours on the 

 pumiceous tuffs and agglomerates composing the mass of the 

 mountain. At the "fabbrica," near the Faraglione, the products are 

 roughly separated by simple machinery, sent from England for the 

 purpose ; but the salts are forwarded to this country for purification. 

 The cone of Vulcano is made up of agglomerates, often well 

 stratified; the materials being much altered through the permeation of 

 the mass by acid gases and vapours, and often exhibit brilliantly 

 variegated tints. Half way down the slope of the mountain, on its 

 northern side, is the little crater called Fossa Anticcha or Forgia 

 Vecchia, the floor of which has a diameter of about 60 yards, while 

 acid vapours are discharged by several fumaroles at its sides. In the 

 sides of this crater, and in a great fissure near it, the characteristic 

 quaquaversal dip of the materials in volcanic cones is well exhibited. 

 The ejected materials are often seen forming beds dipping at angles 

 of from 25° to 30°. (See Fig. 11.) The date of the formation of 

 the crater called the Fossa Anticcha is quite unknown. It is clear that 

 it existed at the time of Spallanzani's visit to the island, and he 

 imforms us that at some earlier period the collection and purification 

 of the products of the mountain had been carried on in it. 



The lava- stream on the north-west side of the cone of Yulcano is 

 composed of obsidian passing into Liparite, and exactly resembles 

 those of the last period of eruption in the adjacent island of Lipari, 

 which were described in the last chapter. Two points in connexion 

 with this lava-stream are, however, worthy of especial notice. 

 Firstly, although of great thickness, it has evidently consolidated on 

 a slope of 35 °, thus affording a striking illustration of the baseless- 

 ness of the opinions maintained by Elie de Beaumont and M.Dufrenoy 

 on this subject, by means of which they sought to support the 

 exploded theory of " Elevation-craters." Secondly, in its wonderfully 

 contorted internal structure, its rent and rugged surface, and espe- 



DECADE II. VOL. II. NO. III. 8 



