()(_) ART OF GLA8SMAKING. 



nealiug, without any cement; and that in this state it was 



more dense, and less liable to hrcak by a sudden trunsitioa 



from cold to hot, or the contrary. Tiie latter property 



v/as confirmed by the experiments of Mr. Ciffle, so that 



he did. not hesitate to consider glass so altered as the most 



proper substance for supplying chemistry with vessels at 



once refractory and not liable to crack. 



Theeftect Mr. Keir, after having described these phenomena, 



ancnbed to ascribed it to the crvstallizalioii of the vitreous matter ; an 

 crystallization- . . .-. ^ ' 



opinion naturally arising from the aspect of the fi%cture, 



which, instead of being coiithoidal, as in transparent glass, 



exhibits, if not facets, at least very decided parallel 



striae. 



This supported The observation? of Mr. d'Artigues strongly support 



^y *^f this explanation. I have myself a mass of glass, found five 



experiment* '^ n ■^ , ^ ,■ ^ 



ot d'Artigues. years ago at the bottom or a crucible at the manutactory of 



St. Gobin, whicii appears formed to afford a demonstration 

 of it; since we can distinguish, even with the naked eye, 

 prisms shooting from the devitrilied crust that constitutes its 

 surface, and which is 2 or 3 mill, [about a line] thick. 

 Riujiihisal- Is, it true however, that all these changes are solely the 

 v,ays thecais. ^^^^^ ^f ^ crystallization? and can we admit with Mr. 

 and is there a d'Artigues,- " that a precipitation takes place throughout 

 precipitation, tjjg mass, each of the component parts obeying at the sam« 

 timjC the laws of attraction" ? Before I attempt to solve 

 Experiments these questions, I shall add a few more facts, resulting from 

 "i ' "^^ ' experimentson this subject made by Mr. d'Arcet, and the 

 consequences of which will naturally find a placeiu thisdis- 

 cussion. 

 Specimen 1. Among the ten specimens from these experiments, which 

 fom'lkner ^^^ P"^ ^^^^ ^^ hands, No. 1 is a piece of bottle glass, which 

 Jeyitrified. was exposed for three days to a heat of 50° of Wedgwood in 

 Reaumur's cement. The devitrification is complete ; inte- 

 riorly it has a rosy tinge ; the fracture exhibits striae, ar- 

 ranged in stars, to the very centre ; it gives no sighs of 

 electricity by friction ; it rather scratches rock crystal, than 

 is scratched by it ; corundum leaves a mark on it scarcely 

 perceptible through a lens. 

 Si^ecimen 2. ^^' 2> exposed to the same fire, the same time, in the 

 Another with same Cement, has barely acquired an earthy crust, which is 

 ^«^- scratched 



