fflS On the Green Colour for Pavttivg, 



When glass is devitrified it has no longer a vitreous 1>at 

 a granulated fracture : it possesses no transparency, and has 

 a perfect resemblance to a stone : it becomes a less bad con- 

 ductor of caloric and electricity. In a word, it is no longer 

 susceptible of being fused at the same degree of heat ; and, 

 to bring it more easily to the vitreous state, it must be first 

 pounded, in order to place in contact the substances which 

 were separated from each other during the crystallization, 

 and which can no longer serve as mutual fluxes. 



I wish the novelty of several of the facts which I have 

 here related, and the consequences T have deduced from 

 them, in proving that the cr^^stallization of glass is a devi- 

 trification, may be sufficientiy interesting to induce che- 

 mists to pay attention to them. I have no doubt they will 

 be able to form many comparisons which escaped me, or 

 which the limits of a single memoir would not allow me 

 to mention. The resemblance of my specimens of devi- 

 trified glass to those of certain kinds of lava ; the possibility 

 that other kinds of lava may have undergone a more abso- 

 lute devitrification by a longer cooling through volcanic cur- 

 rents, or by remaining fluid for whole years under crusts 

 already cooled : every thing, in short, induces me to believe 

 that these facts may aftbrd the means of explaining geolo- 

 gical phenomena respecting which philosophers have not 

 agreed, because nothing could make them believe that stones, 

 had before been glass. 



XLVI. On the leantlful Green Colour for PaintiuQ, u'hlck 

 may he obtained from Chrome. By Godon-Saint- 



W HEN M. Vauquelin made known his ingenious labour 

 on the red lead of Siberia, as the interesting series of the 

 analyses which he published showed him that chrome is 

 dispersed throughout various parts of the earth ; since Ame- 

 rica present? it m the emerald, India in the spinel, and Si- 

 beria in chroniatized lead ; he foresaw that this metal would 

 one dav be found in a natural state sufficientlv abundant to 

 make a useful application of it to the arts, and he indicated 

 the importance of it in a memoir f. The discovery of chror- 

 matized lead ore found in France confirmed the happy eon- 

 je<:tures of this illustrious chemist, and convinced us that 



• Fioni Annnks du Munum Nuiion,d a'lLiloire NuluyelU\ No. 2j. 

 •'■ Annalci Jc Cbimie, Ftvr. 1758. 



the 



