Reflexions on Cobalt^ &c. 



ftate the reafons they have alledged* and 

 juftify the opinion I have followed. 



Of Cobalt. 



2. With regard to cobalt, fome have thought 

 it to be nothing elfe but a compound of iron 

 and arfenic, aflerting that fuch a compound 

 would communicate a blue colour to glafs, 

 but this pretenfion has been fully refuted by 

 the experiments of Mr. Brandt. Mem. Sued* 

 p. 46 and 47. and thofe of Mr. Monnet. Dijfa 

 Des. Mett. p. 279. 



3. Others have thought that the tinging 

 quality is produced in cobalt, merely by its 

 union with arfenic, becaufe it fometimes 

 happens, that cobalt will not tinge, unlefs 

 arfenic be added to it. But the true reafon 

 of this phenomenon is, that cobalt will not 

 tinge unlefs it is dephlogifticated, nor even, 

 then unlefs it melts, and it fometimes hap- 

 pens that cobalt is too much dephlogifticated, 

 and then it will not melt in the ufual heat, 

 without the addition of arfenic, which ferves 

 as a flux to it ; for that arfenic is not other- 

 wife efifential to its tinging property is evi- 

 dent from this, that fomq cobalt ores, which 

 tinge admirably well, are yet abfolutely free 

 from arfenic, fuch as the vitreous ore, Sp. zd< 



It 



