THE ERUPTION OF VESUVIUS IN APRIL, 1906. 237 



yellowish tint from ferrous chloride or organic products, A notable 

 fact is the presence of fluorine in the salmiac. Only a small amomit 

 of water vapor came from the fumaroles, but after each shower 

 abundant vapors of superficial origin were found. These fumaroles 

 became less abundant toward the source, but were numerous in the 

 region Avhere th« lava having left the ancient flows covered the cul- 

 tivated regions. Although a part of the ammonium chloride is of 

 deep origin, it is probable that the slow combustion of organic matter 

 has played some part in its production. The mineral was found to 

 form continuous crusts along the walls of houses in Boscotrecase 

 buried by the lava, in which organic combustion was in progress. 

 A few days after the lava stopped flowing, a road was laid out over 

 the surface. The lava was still warm, and in places the ammonium 

 chloride crystallized between the fragments which formed the road- 

 bed. It was a strange spectacle to see the crowd of people traversing 

 the steaming lava, still incandescent some decimeters from the 

 surface. 



Sublimations of sulphur occur in limited quantity at Boscotrecase, 

 It forms small orthorhombic octahedrons, or a melted glaze, at the 

 orifice of the hydrogen sulphide fumaroles, the temperature of 

 which must have been approximately 100°, and at the most slightly 

 above 118° C. 



FUMAROLES OF THE FISSURES AND OF THE CRATER. 



At the origin of the flows that started from the fissures found 

 at an altitude of 600 meters there were crevasses of greater or less 

 depth, still very warm at the time of my observations. An acid 

 Avater vapor was being given olf. and the edges of the fissures were 

 decorated with chlorides, notably ferrous chloride. These were evi- 

 dently acid fumaroles of deep origin. The same is true of the more 

 active fumaroles on the slopes below the notch of the crater, their 

 temperature being mostlv higher than 400°. The hydrochloric and 

 sulphurous vapors were suffocating, the coating of chloride was 

 much thicker than in the preceding case, and there was a deliquescent 

 mass of chlorides of iron, potassium, magnesium, calcium, etc. There 

 were also crystals of realgar and of sulphur in the cooler parts. 



I examined many specimens collected in the vicinity of the cone 

 in July. There are several covered by small cubes of galena, some- 

 times alone, sometimes resting upon i^yrite, or supporting octahe- 

 drons of magnetite and lamella? of hematite. The cubes have often 

 the hopper form, like those created by sublimation in metallurgical 

 operations. It is the first time that lead sulphide has been observed 

 in a fumarole of Mount Vesuvius, and it was doubtless formed by the 

 reaction of hydrogen sulphide upon the chloride of lead, known 

 for a long time in this volcano. 



