3.' e fats. 243 



it, they must know the quantity of the metal 

 which the ore contains. 



The assayer takes a small specimen, about 

 one-eighth of an ounce. He first, if there is 

 occasion, performs the operation of washing, 

 then separates the sulphur and arsenic by roast- 

 ing, &c., observing with attention what matters 

 are evaporating: he then melts the ore in a 

 crucible with other substances (to promote the 

 fusion and attract the oxygen), of which black 

 flux is the chief, with a quantity of common 

 salt. Sometimes glass or borax are used to bring 

 the metal into fusion, and preserve it from sco- 

 rification; and sometimes pure alkali and char- 

 coal dust are preferable to black flux, as in the 

 case of iron. When a proper heat is applied, 

 the metal appears at the bottom, and by cor- 

 responding weights he calculates how much a 

 hundred pounds of the ore will produce. The 

 operation is nice, and therefore generally requires 

 to be repeated ; as a slight variation in the heat 

 employed to reduce the ore will either fail to 

 give it the necessary fluidity, or too great heat 

 may oxidize some of the metal. 



Metals were formerly divided into 1st, The 

 perfect, or such as could not be calcined or oxi- 

 dized by the application of heat ; and these were 

 gold, silver, and platinum: 2d, Imperfect or 

 base, which might be calcined, but which were 

 malleable; such were mercury, copper, iron, lead, 



M 2 



