The furnace and implements used for assaying in the Royal Mint and the Goldsmiths' Hall, in the city of London, are the following:--
A A A A, _fig._ 58., is a front elevation of an assay furnace; _a a_, a view of one of the two iron rollers on which the furnace rests, and by means of which it is moved forward or backward; _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._ 59., is a perpendicular section of _fig._ 58.; _a a_, end view of the rollers; _b_ 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 section representing the situation 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 6-1/2 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._ 58., 21-1/2 inches; the funnel _e_, 6 inches. The square of the furnace which receives the muffle and fuel is 11-3/4 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._ 60., is a horizontal section of the furnace over the 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.
_Fig._ 61. represents the muffle or pot, which is 12 inches long, 6 inches broad inside; in the clear 6-3/4: in height 4-1/2 inside measure, and nearly 5-1/2 in the clear.
_Fig._ 62., the muffle-plate, which is of the same size as the bottom of the muffle.