Sir H. Davy on the Phenomena of Volcanoes. 89 



fered so much from the exposure to them that I was obliged 

 to descend ; and the effect was not transient, for a violent ca- 

 tarrhal affection ensued, which prevented me for a month from 

 again ascending the mountain. 



On the 6th of January I made another visit to Vesuvius. I 

 found the appearance of the lava considerably changed ; the 

 bocca from which it issued on the 5th of December was closed, 

 and the current now flowed quietly and without noise from a 

 chasm in the cooled lava about three hundred feet lower down. 

 The heat was evidently less intense. I repeated my experi- 

 ments with nitre with the same results, and exposed pure sil- 

 ver and platinum to the fused lava : they were not at all changed 

 in colour. I collected the sublimations from various parts of 

 the cooled lava above. The rocks near the ancient bocca were 

 entirely covered with white, yellow, and reddish saline sub- 

 stances. I found one specimen of large saline crystals in a 

 cavity, which had a slight tint of purple : this examined, proved 

 to be common salt with a minute portion of muriate of cobalt. 

 The other sublimations consisted of common salt in great ex- 

 cess, much chloride of iron, some sulphate of soda ; and by 

 the test of muriate of platinum, there appeared to exist in them 

 a small quantity of sulphate or muriate of potassa ; and a so- 

 lution of ammonia detected the presence of a minute quantity 

 of the oxide of copper. 



During the months of January and February I made several 

 visits to the top of Vesuvius: I shall not particularize them 

 all ; but shall mention only such as afforded me some new ob- 

 servations. On the 26th of January, the lava was seen nearly 

 white hot through a chasm near the place where it flowed from 

 the mountain. I threw nitre upon it in large quantities through 

 this chasm, in the presence of H. R. H. the Prince of Den- 

 mark, whom I had the honour of accompanying in this ex- 

 cursion to the mountain, and my friend the Cavaliere Monti- 

 celli : there was no more increase of ignition than when the 

 experiment was made on lava exposed to the free air. The 

 appearance of the sublimations was now considerably changed : 

 those near the aperture were coloured green and blue by salts 

 of copper; but there was still a great quantity of muriate of 

 iron. I have mentioned, that on the 5th the sublimate of the 

 lava was pure chloride of sodium : in the sublimate of January 

 6th, there were both sulphate of soda and indications of sul- 

 phate of potassa. In the sublimates that I collected on the 

 26th, the sulphate of soda was in much larger quantities, and 

 there was much more of a salt of potassa. From the 5th of 

 December to the 20th of February, the lava flowed in larger 

 or smaller quantities, so that at night a stream of ignited mat- 



New Series. Vol. 4% No. 20. Aug. 1828. N ter 



