55 ART OF GLASSMAKING. 



Artificial The volcaiiic glass, thus brought bnck to the state of very 



touchstones of compact and very fine-grained lithoid lava, induced Mr. 

 d'Arcet to have some polished, to serve as touchstones ; and 

 the trials he made leave no doubt, that they would supply 

 the place of the native stones of the best quality, which are 

 becoming very scarce. 



the best 

 quality 



Examination of what constitutes the real differmce between 

 transparent and demtrijied glass. 



Will crystalli- Can the facts I have recorded be explained by simple 

 ^oft"c facts""* crystallization ? or, to express myself more clearly, can ihey 

 be reconciled with the kuowti effects of this transition of " 

 substances to the regular con6rfcte state, and with the hypo- 

 thesis of a simultaneous precipitation of some 6f their fixed 

 elements? This remains for tne to examine. ''' '^ 



In the first place, we may observe, that, if thet'C were a 

 crystallization and precipitation at the same lime, the opake 

 mass resulting from these would no longer be crystallized 

 glass, but the product of its decomposition. 



In the next place, if there were in reality a separation of 

 some of the ingredients of the glass, they should exhibit, in 

 some yiarts at least, the appearance of the colours, the de- 

 gree of hardness, and the other characters peculiar to them; 

 of which we do not perceive the least indication. 



Lastly, on this supposition, the state of combination 

 having ceased, the particles abandoiud should be imraedii 

 ately given up to the chemical action of their solvents : but 

 it is certain, that nothing is taken up from devitrified glass 

 even by the most potent acids, assisted by a boiling heat. 

 It must be acknowledged therefore, that their union stiU 

 subsits ; and even that it is fnore intimate, since it is this 

 that constitutes bodies the most homogeneous, most solid, 

 hardest, and most capable of resisting fusiori and solu- 



ist objection. 



f.'d objectioa. 



3rl objection. 



Devinified 

 gla»s fu>ible 

 acjain u'luui 

 powdered. 



According to Mr. d'Artigues, devitrified glass becomes 

 fusible; again, when, by reducing it to powder, the matter 

 which had been separated, and which serve reciprocally a» 

 fluxes to each other, are again brought into contact. I con- 

 ceived it was a proper subject for experiment to decide, 



whether 



