58 EXPERIMENTS on WHINSTONE and LAVA. 



" bafe des laves ; que ce feu agit difFeremment que le feu de 

 " nos fourneaux, tel que nous Pemployons dans la chimie et 

 " dans les arts ; qu'il produit dans les laves une fluidite qui 

 " n'a aucun rapport avec la fluidite vitreufe, que nous operons, 

 " lorfque nous traitons a grand feu les memes matieres qui leur 

 " fervent de bafe, et lorfque nous voulons rendre aux laves elles 

 " memes leur fluidite. Celui des volcans n'a point d'intenfite ; 

 " il ne peut pas meme vitrifier les fubftances les plus fufibles, 

 " tels que les fchorls, qui fe trouvent comrhe parties confli- 

 " tuantes dans l'interieur des laves ; il produit la fluidite par 

 " une efpece de diffolution, par une fimple dilation, qui permet 

 " aux parties de gliffer les unes fur les autres, et peutetre encore 

 " par le concours d'une autre matiere qui fert de vehicule a la 

 " fluidite." 



Mr Kirwan cenfures this fuppofition as ftrange and incon- 

 ceivable ; but in my opinion, that which he has brought for- 

 ward is not lefs fo. In the Elements of Mineralogy , fecond edition, 

 vol. I. p. 396. he fays : '' Now, there are but three forts of fu- 

 " fion with which we are acquainted : that which produces por- 

 " celain ; that which produces enamels and femi-vitrifications ; 

 " and that which produces glafs. By infpeding lava we fliall 

 " find that very little of it has been in any of thefe ftates ; fince 

 " therefore it has flowed, it is plain it has derived its liquifac- 

 " tion not from the fufion of its own materials, but from that 

 * c of fome foreign fubftance mixed with it. This facT: is fo plain, 

 " that it has even flruck M. Dolomieu, in the midfl of his 

 " prepofl'efhons, in favour of fome ftrange inconceivable power, 

 " which he attributes to volcanic fire, of melting earthy fub- 

 " fiances, without effecliing an alteration in their fenfible quali- 

 " ties. " I hope," fays he, " to prove, that lavas contain, in 

 " their interior, a combuflible matter, which burns and con- 

 ** fumes in the fame manner as other inflammables," IJles Pon- 

 " ces, 10. Yet he neglecls telling us what this matter is; though 

 u it plainly appears to be no other than fulphur and bitumen, 



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