60 



DEVITRIFICATION OF GLASS. 



denominated die cementation of glafs, and the product was 

 called Reaumur's porcelain: no incident could be more effect- 

 ually calculated to retard the true developement of the fact 

 tuan fuch a denomination of this kind. 

 Repetitions of The labours of Bofc d'Antic upon the fame object were 

 the procefs by a ]f directed to no other purpofe than that of obtaining a good 

 otbc"jl C ^ pottery by this means, and of afcertaining what cements were 



the befl calculated to give new properties to this body. Thus 

 it was that by calling the procefs by the name of cementation, 

 which depended in no refpect upon what was added as the ce- 

 ment, others were mifled, who were induced to follow the 

 couife of experiments already began. The natural confe- 

 quence was, that fcience gained nothing refpeding this procefs 

 iince the time of Reaumur. Many have fince attempted the 

 cementation of glafs without perceiving any new refult in the ' 

 product. 

 Obfervation of Several perfons have fince admitted the property in glafs of 

 cryftab in glafi. affording cryftals ; but thefe remarks being more efpecially 

 made by artifts, placed by their fituation at the head of glafs- 

 works, have not afforded the fcientific cnnfequences which 

 might have been deduced from them. The directors of a great 

 efiablifhment have feldom time to dwell upon the contempla- 

 tion of fmall effects; they are obliged to attend to too many 

 things at the fame time. Thefe remarks, though ohrious in 

 themfelves, remained without connection ; and no one thought 

 or ventured to publifh that the cryftallization of glafs, and ce- 

 mentation by the procefs of Reaumur are abfolutely one and 

 the fame thing. 

 Experiments of Sir James Hall,* in his valuable experiments upon whin- 

 Sir James Hall flone and lava, publifhed in the 14th volume of the Biblio- 

 mi w in one, t | ie q ue Britannique, ascertained the property of thefe ftones to 

 become fufed into glafs, and to return to theftony ftate, ac- 

 cording to the circum fiances. 

 He did not pur- He called this laft fad a devitrification. He faw that it was 

 ficnion amone" ^ ie e ^ ec ^ °' a precipitation, and explained it in a manner that 

 artificial pro- was highly Satisfactory and true; but being too much occupied in 

 deducing from this fact arguments in favour of the volcanic geo- 

 logy, he neglected purfuing the inlerefting philofophical confe- 

 rences to which the phenomenon pointed the way. This is 



* Firft in the Edinburgh Tranfaclions, and afterwards in our 

 Journal. N. 



4f the 



