

Natural History. 181 



volcano and its lavas, the latter was soon found in the fumes from the 

 crater, and also from the fumaroles in the lava, but on continuing 

 their researches these philosophers were led to conclude, that the 

 sulphurous acid is n.ot contained icady formed in the lava, but is de- 

 veloped by the contact of the air ; fragments of red-hot lava plunged 

 into tincture of turnsole, not changing its colour, whilst those which 

 had been cooled in the air easily turned it red. 



Sulphur in crystals is not found in the crater. It is requisite for 

 its production that the temperature of the surface of the crater or of 

 the lava should be below 212° F. The sulphurous acid only appears 

 when the temperature is sufficient for the combustion of the sulphur, 

 and the Contact of the external air is necessary to its production. 

 Thus the distinction of volcanoes into two classes, namely those 

 which with Vesuvius, produce muriatic acid, and those which with 

 the Sol fate rra, produce sulphurous acid is unfounded; since the two 

 acids appear at Vesuvius according to the temperature, and since the 

 Solfaterra does not really produce sulphurous acid, as has been till 

 now supposed, but muriatic acid free and combined, carbonic acid, 

 and sulphuretted hydrogen. 



The lava which flowed from the crater on the 26th Feb. was of 

 a deep bluish-grey colour, and a fine grain resembling basalt; it was 

 composed of grains of pyroxine as large as a hemp seed, crystals of 

 amphigine, mica in very brilliant small plates, olivine ? in transparent 

 and yellow grains, but rare, and finally of portions of a black pumice 

 as big as nuts and incorporated with the lava. 



Volcanic Electricity. — In October of the same year the mountain 

 again became active, and an eruption took place one of the most dis- 

 astrous that Vesuvius ever gave rise to. After frequent ejections of 

 ashes, 8cc. from the summit, earthquakes, fyc, the lava appeared 

 about mid-da}' of October 21, 1822, on the border of the crater, and 

 came down in two streams. On the 22nd an enormous column of 

 fire 2000 feet high, rose from the top of the mountain, whilst a rain 

 of hot sand, pumice stones, and lava fell. About 2 o'clock P.M.; the 

 first signs of electricity manifested themselves in that part of the at- 

 mosphere situated round the column of sand, \jhich rose from the 

 crater in the form of a pine, and shortly, numberless zig-zag flashes 

 continued without ceasing, to penetrate the cloud of cinders without, 

 however, giving rise to any detonation that could be heard. Towards 

 the evening the thunders commenced just as the volcano took, for a 

 short time, an appearance of repose. 



About 8 o'clock our philosophers took the opportunity of the 

 short calm and approached the mountain, just as a fresh and more 

 vigorous eruption took place. Soon the whole heaven seemed on fire 

 from the immense quantity of ignited matter thrown up into it. 

 Towards the middle of the night the paroxysm of the volcano seemed 

 to have risen to its height, but whilst the operations of the crater 

 became more and more feeble, the play of electricity, which embel- 

 lished the elevated region of the clouds of sand, became stronger 



