[ 134 1 [Book VI, 



CHAP. XXIV. 



COBALT. 



. I Hijlory of Cobalt. Analogy between this Metal and the blu& 

 colouring Matter of Vegetables. Mode of ajjaying it.- Mines of 

 Cobalt. Smalt, or Ponvder Blue. Ufes of Cobalt in the Arts. 

 Curious fympathetic Ink. Changeable Landscape. r Union ivith 

 cihir Metals. 



COBALT has never been found native, that is, 

 in a metallic ftate, but is almoft always calcined 

 t>r united with arfenic, the arfenical acid, fulphur, iron, 

 vitriolic acid, &c. Minerals containing cobalt are 

 frequently of a pink colour, which arifes from the 

 pretence of arfenical acid, and this colour is deftroyed 

 by fire, in proportion as the acid is diflipated. When 

 united with vitriolic acid, it alfo is fometimes reddiftr : 

 the effect of acids on cobalt points out an analogy 

 between it and the blue colouring matter of vege- 

 tables. 



To afTay cobalt ores, the operations of pounding, 

 wafhing, and roafling, muft be all employed. The 

 cobalt remains in a ftate of black calx, more or lefs 

 deep with refpect to colour ; this is mixed with black 

 flux and a fmall quantity of decrepitated fea-falt ; the 

 fufion is performed in a forge heat in a covered cru- 

 cible, which muft be (lightly agitated, to precipitate 

 the metal as foon as the fufion is complete. The me- 

 tallic button is fometimes found to confift of two dif- 

 tint fubftances, cobalt being uppermoft, and bifmuth 

 beneath ; a ftroke of the hammer readily feparates 

 them. 



The 



