466 DOMAIN XII. VOLCANIC. 



of a glass-house, without the addition of any flux 

 or dissolvent, a fine and shining glass, of the most 

 beautiful black, is obtained in a few hours. When 

 it is in a mass, this glass is very opake ; but in 

 breaking and reducing it into thin plates, it is 

 found to be transparent, but a little coloured by a 

 fuliginous substance. 



" If the substance submitted to this experiment 

 is derived from a trap, the glass is then of a 

 greenish colour, and is much more transparent on 

 the edges. It may even be refined by the assist- 

 ance of soda, so as to form a fine bottle glass ; 

 which does not happen when basaltic lava is used 

 instead of trap ; for, in the latter instance, the 

 substance cannot be blown but with difficulty, and 

 without success : and the glass is neither good nor 

 transparent. I know the contrary has been as- 

 serted in a work on chemistry ; but experiments 

 that I made in the presence of well-informed men, 

 in 1784, in the glass-house of Sevres, near Meu- 

 don, and of which I have preserved the minutes, 

 demonstrate that basaltic lava used alone, can in 

 no instance make bottles : that it is neither im- 

 proved by soda nor potash, but other substances 

 must be added to it. 



" The theory of volcanic glasses, obsidians, and 

 amels, needs not be sought elsewhere. If I distin- 

 guish amels from other vitreous productions, pro- 



