64 EXPERIMENTS on JVHINSTONE and LAF^l. 



ftream on three diflerent days. It was in general concealed by 

 a thin white fmokc, which the wind blew aiide occafionally, 

 fo that I could diflincfUy fee the lava as it biirft from the fide of 

 the hill. It was then of a bright white heat, and flowed with 

 the agility and rapidity of water, in all refpedls refembling melt- 

 ed iron rvmning from the furnace. The liquid, at its firfl; emer- 

 gence, manifefted a ftrong effervefcence, which fubfiding as the 

 heat abated, fliewed itfelf at laft only in the burfting of fome 

 very large bubbles, accompanied with a white fmoke. Where 

 I approached the ftream, it was ftill of a ftrong red heat, and 

 had the confiRence of honey. I thruft a ftick into it with 

 cafe, to the end of which fome of the lava adhering, by its 

 vifcidity, allowed itfelf to be drawn out into threads, and was 

 found, when cold, to have a fliining furface, and a vitreous 

 fradlure. 



Being thus convinced that I had met with a lava of glafs, I 

 prepared fome moulds of flvicco, in which I meant to take cafts 

 with that rare fubflance ; and with this view retvtrned to 

 the mountain. I found the ftream was not fo liquid as at firft, 

 but I was able, by means of a ladle fixed on the end of a pole, 

 to lift the fpecimen now before us in a flate like dough. I 

 then prefled it with a feal, by which means, though too coarfe 

 to receive an accurate imprefiion, it took the fliape it now 

 bears, which is that of the ladle. It is very porous, one- 

 third of it nearly being occupied by air holes. It contains a 

 great number of fmall white cryilals of Vefuvian garnet, em- 

 bedded in a black fubftance, which completely refembles the 

 glafs obtained in our experiments from lava by rapid cooling 

 after fufion. Befides all their other properties, it pofl^eflTes the 

 fufibility of the glaffes, fince it foftens completely at i8, that is, 

 14 or 15 degrees below the foftening point of any of the flony 

 lavas. Being expofed to the procefs of regulated cooling, it 

 gave the fame refult as all the other lava glaffes. In the lower 



points 



