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XLV. Memoir on the Devitrification of Glass, andtheVhce- 

 nomena tvhich take place during its CrystulUzation. By 

 Dartigues*; Read in t lie Physical Class oj the Insti- 

 tute, May 20th f lS04t. 



OoME chemists have considered glass as a crystallization : 

 this opinion appears to be natural, in consequence of the 

 transparency of" glass or crystal, since we have borrowed the 

 name of the latter to denote a regular and spontaneous ar- 

 rangemeut of the moleculaeof bodies; but, on a little reflec- 

 tion, we discover our error : glass, indeed, never affects the 

 crystalline form, either at its surface or on its fracture; it 

 never exhibits crystals of its own substance, as is remarked 

 in certain metals properly cooled ; and if crystals are formed 

 ill the mass of glass, ihcy are foreign to the part still vitri- 

 fied; thev may be considered as a retrograde step of vitrifi- 

 cation; this 1 shall prove in the course of the present me- 

 moir. 



Beginning with a definition of vitreous fusion^ I shall 

 distinguish and separate that of bodies fusible by themselves 

 in the fire of our furnaces ; such as bocax, phosphoric and 

 other acids. Here caloric, being condensed, softens and 

 fuses the substances, which retain more or less, after they 

 have cooled, transparency and the other physical proper- 

 ties of glass, with which every body is acquainted. 



But I ought to examine and describe that fusion experi- 

 enced by the vitreous compositions employed in the com- 

 mon purposes of life; in the latter case, vitrification is the 

 result of a double phaenomenon; it is not onlv the efl^ect of 

 caloric accumulated, but it is produced also by the aflSnity 

 of the substances v;hich enter into the mixture. Those sub- 

 stance which tend to combine aivd to penetrate each other, 

 -exercise the laws of their aflinity the moment they have at- 

 tained to a sufficient temperature. It is thus that several 

 earths, when united, fuse at a degree of heat at which each 

 of them separately would not have changed its state. 



Thus con)mon vitrification, among ditferent and hetero- 



• Dartigues, proprietor of glass manufacrorics and other csrablishments 

 nt Voricch'j, (S«mbrc-ct-Mcusc) cngHjjcd to suLmic to tiit- miiitutc a trea- 

 tise on the art of ^/as.'-muiin^, to serve as a continuation of the W;n <i>:J 

 Me-ii.rs of tl»c academy. The tiist part is ready for pubhcation ; a gieat 

 ir.any of the platei ;irc engraved, 'i'lie second pirt contains the applica- 

 tion of glass in the ditTcrcnt arts in which it is einp'.oyed. The third part 

 consist) of d-,tached memoirs on tlic physical and chemical properties of 

 glass. The present dissertation is an extract fro:Ti one of the ^e memoirs, 

 t Fion J'i/:r!.'- dc Cbsmir, No. : jo. 



K 2 • gcncous 



