THE HISTORY OF CHEMISTRY, 



colour, from Egypt, and pieces of glafs of tht 

 fame dye from the ruins of Herculaneum, are 

 yet in exigence. Hence it has been concluded 

 by fome, that the uie of cobalt was known to 

 the antients: Though the more modern che- 

 mitts* rather queflion it ; as by all the trials to 

 which they have fubjected the fpecimens of 

 their art, they difcovcred traces of lapis lazuli, 

 iron, or copper, but no cobalt. 



Among the collecflion of ftoncs in the academy 

 of Upfal, are preferred fome glafs checquers, 

 found in Herculaneum, which have an azure tint, 

 arc tranfparent, and feem to owe their gold co- 

 lour to a thin plate of yellow glafs, to which they 

 are very ikillfully united. But they are by no 

 means coloured with cobalt. For having only -4 

 flight bluiih tint, if they are examined by the re- 

 fracted rays of light, the redncfs characleriflic of 

 cobalt will not be found in them. Befidcs, when 

 fmull pieces of thefechecquers are melted by the 

 blow-pipe upon charcoal, either alone or with 

 borax, the red and opaque hue of copper is eaii- 

 ly difcovcred. 



The ores of cobalt, which, together with fil- 

 ver, contain bifmuth, ftiould have fuggefled the 

 application of the blue fcorta to fome ufeful 

 purpdc f : But they were long reckoned amon;? 

 the refufe only; until Seb. Prcufder ellablimeii 

 a mari'^faclory for giafs with cobalt, in Bohemia, 



in 

 * Ccl. Grncl.'r.. in Aftis Goctin. * 



t Encclius dc re n:etd!ica. 



