38 CATALOGUE OF PHILOSOPHICAL APPARATUS, &c. 



the crater in its unaltered and altered condition, together with 

 the various sublimations found in it, such as sulphur, alum, and 

 Sal Ammoniac. The presence of Sal Ammoniac in this crater 

 presents a difficulty in the way of Bunsen's mode of explaining its 

 occurrence in lavas, as he would make it depend upon the existence 

 of organic matter at the spot where it was generated. See for a 

 more probable explanation " Volcanos," supplement, p. 812. 



This is an example of trachyte emitted from a volcano as a 

 current, a somewhat rare occurrence, for, as might be expected 

 from its approaching nearer in composition to granite than ordi- 

 nary lavas, it more generally forms its nucleus, as at Rocca Mon- 

 fina, Astroni, &c. 



Drawer 102. Limestones and Dolomites ejected from Vesuvius. 



Drawers 103, 104. Variety of Vesuvian minerals. 



Such as Meionite, Humite, Tourmaline, Comptonite, Wollastonite, 

 Leucite, Mica, Apatite, Nepheline, Idocrase, Olivine, Melanite, 

 Sodalite, Fer oligiste, Galena, &c. 



Drawer 105. Dykes with the rocks traversed by them, consisting of Leucitic 

 porphyries very different from the present lavas of Vesuvius. 

 Monte Soinma. 



Drawer 106. Masses ejected from Monte Somma, and from the cone of 

 Vesuvius. 



Drawer 107. Older lavas from Vesuvius, the date of which is not known. 



These lavas have the same composition as those at present ejected, being intimate mixtures 

 of two minerals, Labradorite and Augite. 



Labradorite RO, Si O 3 + A1 2 O 3 , Si O 3 , 

 Augite 3RO, 2SiO 3 -RO being either Lime, Magnesia, Protoxide 



of Iron, or Protoxide of Manganese. 



By comparing this with the composition of trachyte or granite it will be seen, that the pro- 

 portion of Silica is less, whilst that of the bases present is greater, than in the latter. 



Drawers 108, 109. Lavas from Vesuvius of known dates. 



Amongst these are specimens of the currents of 1551, 1734, 1751? 



1760, 1767, 1771, 1775, 1779, 1794, 1805, 1807,1809,1810,1822, 



1845, 1855, 1858. 

 Sublimations from Vesuvius. 

 Specimens of lava stamped while still hot. 



