Observations and Experiments made at Vesuvms. 91 



again from below or traversed hy Jiimeroles ; and our authors 

 then perceived in the interstices of these aggregates sulphur in 

 small octahedrons and in needles (an extremely rare kind of 

 sublimate in this volcano), as well as sulphate of lime in silky 

 filaments. 



Nos. 5 and others. They also observe that under these cir- 

 cumstances the vajwurs exhaled abound with liydrochloric 

 acid. 



No. 9. These vapours, by attacking, on the one hand, the 

 iron of the lavas, and by depositing in them on the other hydro- 

 chlorate of copper, have tinged the internal edges of some of 

 the mouths with all the colours of the rainbow; and in the in- 

 terior of a volcanic gulf was found a considerable deposit of 

 snow impregnated with a small quantity of common salt. 



No. 1 3. Pulverized nitre thrown ujwn the viscous paste of 

 flowing lava does not detonate at all, and becomes liquefied 

 without producing the slightest spark. 



No. 14. This lava in a state of fusion exhibits no appear- 

 ance of electricity. This tact was ascertained by every possi- 

 ble experiment. 



No. 1 5. Upon plunging a tube of glass an inch in diame- 

 ter, and the twelfth of an inch in thickness, into an incan- 

 descent crevice, it remained for thi'ee minutes without melting ; 

 the extremity of a bar of iron in the same situation became 

 red-hot in five minutes. 



No. 1 6. Distilled water in which flowing lava is extinguished 

 contracts no acidity from it; but it dissolves a great deal of 

 hydrochloric acid, and a little sulphuric acid in a state of com- 

 bination; and some lime. It does not appear that lava rapidly 

 cooled absorbs any atmospheric air. 



Nos. 17 and -tS. The most abundant smoke of burning 

 lava has only a slight smell of hydrochlorate of iron and o. 

 copper. It did not change the colour of turnsol or violet paper 

 either to red, or to greeji, and is composed of little else than 

 aqueous vapours. The sublimed bodies do not begin to deposit 

 themselves until the temperature of the current diminishes. 



Nos. 4:3 and 19. It is necessary to distinguish three ope- 

 rations in the production or in the manifestation of the sub- 

 stances which are usually attributed to ftancroles : 1°. The 

 local formation : 2°. The deposit of volatile substances occa- 

 sioned by the diminution of the temperature : 3°. The operation 

 of efflorescence. These three effects are explained and deve- 

 loped pp. 63, G*. 



No. 21. Sea-salt or chloride of sodium does not appear to 



be completely fbnncd in the fumavles; the operation of" heat 



M'2 is 



