37 



not to leave this subject, without mentioning the at- 

 tempts made by the moderns to render glass pliant 

 and malleable. There is achymical composition, well 

 known, formed of silver dissolved in acid spirits, 

 which is called cornu lun, a transparent body, easily 

 put into fusion, and very like horn or glass, and 

 which will bear the hammer. Borichius makes men- 

 tion of an experiment of his own, tending to prove 

 the possibility of rendering glass ductile, it consisted 

 in composing a pliant avid malleable salt, for the 

 making of which he gives the receipt ; concluding 

 from thence, that as glass for the most part is only 

 a mixture of salt and sand, and as the salt may b<3 

 rendered ductile, it ought not to be looked upon as 

 impossible that glass may be made malleable. And 

 he imagines that the Roman artificer, spoken of by 

 Pliny and Petronius, may have assumed antimony as 

 the principal ingredient of his glass. Besides wo may 

 observe, that nature hath formed many bodies, having 

 an analogy to that of glass ; such as the horns of 

 animals, amber, the liussian talc, and several others, 

 all which are transparent, and at the same time pliant 

 and malleable. Descartes also takes notice, that salt 

 inay be rendered malk-able, and for that very reason 

 intimates that it is possible to succeed in giving the 

 same property to glass. And Morhotf assures us 7 that 

 the celebrated Boyle was also of this opinion. In 

 speaking of glass, I may add, that the art of paint- 

 ing, so far as it depends upon chymistry, was carried 

 formerly to a much Jiig her degree of perfection, than it 

 is at present. Of this we have striking instances in 

 the windows of some ancient churches, where paint, 

 ings present themselves in the most vivid colours, 

 without detracting from the transparency of the 

 glass; and which, as Boerhaave observes, are hardly 

 to be imitated at present, we having lost the secret 

 to a degree, that there are scarce any hopes of ever 

 recovering it. The enamelling and mosaic works of 

 the ancients yield the same kind of evidence oi their 



