820 



SILVER ASSAYING 



the metal from which we wish to part the oxides must not be volatile : it should also 

 melt, and fopn a button at the heat of cupellation ; for, otherwise, it would continue 

 disseminated, attached to the portion of oxide spread over the cupel, and incapable of 

 being collected. 



Furnace and Implements. The cupel lation-furnace and implements used for assay- 

 ing in the Koyal Mint and Goldsmiths' Hall, in the City of London, are the fol- 

 lowing : 



A A A A (fig. 1 817) is a front elevation of an assay-furnace : a a, a view of one of tho 

 two iron rollers on which the furnace rests, and by means of which it is moved for- 



1817 



1818 



ward or backward j "b, the ash-pit ; c c are the ash-pit dampers, which are moved in a 

 horizontal direction towards each other for regulating the draught of the furnace ; d, 

 the door, or opening, by which the cupels and assays are introduced into the muffle ; 

 e, a moveable funnel or chimney by which the draught of the furnace is increased. 

 B B B B (fig. 1818) is a vertical section of Jiff. 1817: a a, end view of the 



rollers' ; b f the ash-pit ; c, one 

 of the ash-pit dampers; d, 

 the grate, over which is the 

 plate upon which the muffle 

 rests, and which is covered 

 with loam nearly one inch 

 thick ; f, the muffle in sec- 

 tion, representing the situa- 

 tion of the cupels; g, the 

 mouth-plate, and upon it are 

 laid pieces of charcoal, which, 

 during the process, are ignited, and heat the air that is allowed to pass over the 

 cupels, as will be more fully explained in the sequel ; h, the interior of the furnace, 

 exhibiting the fuel. 



The total height of the furnace is 2 feet 6 inches ; from the bottom to the grate, 

 6 inches ; the grate, muffle, plate, and bed of loam, with which it is covered, 3 inches ; 

 from the upper surface of the grate to the commencement of the funnel, e, fig. 1817, 



18-2K 



1824 1822/ 



1828 



300?] 



^E0 



EEE 



~SQ 



21i inches ; the funnel e, 6 inches. Tho square of the furnace which receives the 

 muffle and fuel is 11| inches by 15 inches. The external sides of the furnace are 

 made of plates of wrought iron, and are lined with a 2-inch fire-brick. 



c c c c (fig. 1819) is a horizontal section of tho furnace over tho grate, showing the 

 width of the mouth-piece, or plate of wrought iron, which is 6 inches, and the opening 

 which receives the muffle-plate. 



