ITALY. LETTER XI. l6l 



27. Salmiac [fal ammonlacum nativum) is fub- 

 limated in the cracks and fiffures of the inner 

 funnel of Vefuvius, and is pretty common. It is 

 iikewife fublimated in Solfarara. It appears either 

 in folid undetermined or cryftallized lumps, and 

 proves the prefence of the acid of common fait 

 and of a volatile mineral alkali, which are requi- 

 fite to its production. What is ftill more remark- 

 able is its appearing in the cracks, fiffures, and 

 furface, of the erupted lava-torrents, where it be- 

 gins to fublimate about two months after the erup- 

 tion, when the lavas begin to cool. This proves the 

 pre-exiftence and not the evaporation of the volatile 

 fait in the mixture of the hot lava. It is, perhap?, 

 produced in the lava. Or did it pre-exift in the 

 mountain ? Whence comes this volatile alkali ? 

 Cannot many other falts have exifted in the lava? 

 And what wonder is it then that, the lavas incline 

 to cryftallize into regular determined forms, either 

 in their whole mafies or in feme particles? The 

 Vefuvian guides gather and fell the Salmiac at 

 Naples, where it is employed to fcower or to tin 

 iron or copper vefTels. The Vefuvian Salmiac is 

 white ; but that of Solfatara is yellowim. 



Among the devaluations of the different erup- 

 tions of Vefuvius, the mod remarkable indeed is 

 the covering and burying of three cities. They 

 cannot have been very large > nor very confider- 

 M able, 



