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SECTIONFIRST. 



Its Relation to Heat and Fixed Air. 



This ftone expofed to a heat of 130° Wedgwood, in com- 

 mon clay crucibles, vitrifies very readily when in contadl with 

 the crucible, but the interior part remains unchanged. Having 

 heated two ounces of it in a black lead crucible, only a very 

 fmall part of it was vitrified ; the remainder was converted 

 into lime by a heat of 140°, and lofl 194 grs. that is, little 

 more than 20 per cent, of its weight ; fubfequent experiments 

 fliewed that the weight tlius loft is fixed air, and that the 

 lofs is ftill greater than this experiment indicates, as by reafon 

 of the partial vitrification it cannot be perfedlly afcertained. 



Equal parts quartz and Stronthian lime, melted in a heat 

 of 138°, partly into an amber yellow glafs, and partly into a 

 black and white enamel, the furface prefented a ftrong le.ad- 

 coloured metallic glaze, which was communicated even to the 

 interior of the crucible and to its cover. 



Two parts of this lime and one of magnefia being heated to 

 138°, the lime vitrified with that part of the crucible with 

 which it was in contadl into a porcelain mafs, and acquired 

 a purplifli and greenilh colour ; the magnefia remained unal- 

 tered. 



Four 



