262 On the Devitrification of Glass, 



pure and transparent. These crystallizations, always nu- 

 inerous and very regular, excited my curiosity, as they had 

 done that of several glass manufacturers before. I collected a 

 large quantity of them; and I carefully selected the most 

 cunous, and those which exhibited the most extraordinary 

 characters. 



B. comparing the pieces I had obtained, and the circum- 

 stances under wliich they were produced, and by making 

 remarks, attempts, and experiments to imitate at pleasure 

 these crv>tallizati()ns, I was soon able to distinguish diflcrent 

 classes of them, all produced by the nature of the different 

 substances which enter into tlie con)position of glass. I 

 fha'.l here take a fhorl view of them : I shall not, however, 

 speak of devitrification^ which almost always takes place in 

 the scoriae of forges; every body has been able to remark it, 

 and may account for it by what I am about to say. 



T he first remark which may be made is, that the more in- 

 gredients there are in glass, the more susceptible it is of 

 beir.g speedily and easily devitrified : but as a solvent charged 

 with a great quantity of saline substances suffers them to 

 crystalhze in a more confused manner, it is also not in these 

 kinds of glass that the most regular crystallizations are re- 

 marked; a precipitation is eHected in the whole mass; each 

 of the mgredicuts obeys, at the same time, the laws of af- 

 finity : tran^^parcucy disappears speedily, and in a little 

 time nothing more is perceived than a stone instead of a 

 vitreous body". Amidst this chaos, it is however impos- 

 sible not to discover the rudiments of crystallization. Such 

 arc the phenomena exhibited in their devitrification by glass 

 bottles, which approach near to glass entirely earthy, since 

 very few salts enter into their composition.. 



Any person may keep a common glass bottle in a heat 

 long enough continued, and capable of softening its paste; 

 soon after it cliauges its colour, becomes crav, and has the 

 appearance of earthen ware. Such is the porcelain of Reau- 

 mur; but it is seen that there is nothing here which has the 

 least resemblance to cementation. 



No'v, instead of observing the pha^nomenon in so small a 

 mass, if I search the bottom of the furnaces in which such 

 bottles are fused, 1 find that the glass is absolutely devitri- 

 fied, and that it even has assumed so stony an appearance, 

 that the most expert eye can scarcely distinguish the brick 

 of which the furnace is, constructed from the part which 

 has been glass. It is only bv following, in the fragments 

 less advanced, the progress of the devitrification, that one 

 can distinguish the glass in a granulated stone, which has 



rath«r 



