$2 Observations and Ex})criincn(s made at Vesuvius. 



is probably only to disengage it from the lava in which it 

 doubtless exists. Sulphurous acid is produced only when the 

 air comes in contact with incandescent lava. The various 

 salts which have alkaline bases, effloresce on the surface of the 

 clods or lumps of lava and scoriae, without the exposure of them 

 to fumerolcs. 



No. 43, 10 and 11. Chloride of sodium is one of the salts 

 which are found in the greatest abundance in the products of 

 Mount Vesuvius; the masses of lava, the scoria?, the pumice- 

 stone, the sand, &c. are all impregnated with it: next to 

 sea-salt, the most abundant are: 1°. the sulphates of lime, 

 soda, potass, iron, and copper: 2°. the chloride of potas- 

 sium, the hydrochlorates of iron, of copper, and perhaps of 

 lime. 



No. 22. Lava, at a red heat, does not contain acids in a 

 free state ; these acids are only developed at a lower tempera- 

 ture, and upon contact with the air. Hydrochlorate of iron 

 is disengaged while the lava is at its highest temperature. 

 There appears however to exist a large quantity of sulphur, 

 which disenijafres itself even after the lava has ceased to flow. 



No. 26. On one occasion when the fumeroles were very 

 active, the operation of sublimation at its maximum, and that 

 of efflorescence at its minimum, our authors perceived a 

 powerful smell of sulphurous acid, but were unable to distin- 

 guish any smell of hydrgchloric acid. 



No. 29. The volcanic sand which falls upon snow contri- 

 butes to preserve it from melting, by protecting it from the heat 

 of the sun, of which it appears to be a very bad conductor. 



No. 30. This sand is partly composed of very small por- 

 tions of lava projected into the air in a liquid state, and sud- 

 denly cooled, and partly of solid substances pulverized by 

 iiiction. 



No. 31. It has the taste of sea-salt, and a sensible odour 

 of free hydrochloric acid, which however is dissipated in a 

 few days. 



Nos. 32 and 33. The other substances which enter into its 

 composition are, the hydrochloric, sulphuric, and silicic acids, 

 soda, potass, lime, alumina, the oxides of iron and manganese, 

 and a little magnesia. The predominant substances are, 

 chloride of sodium, sulphate of lime, oxide of iron, and alu- 

 mina. 



No. 34. Lava, at least that which was taken from the sur- 

 face, when subjected to the blowpipe, melts readily and with 

 effervescence, and is converted into a black shining enamel. 

 It contains 9"29 per cent, of chloride of sodium, and some 



traces 



