822 SILVER ASSAYING 



and useful. Upon it are placed the cupels, which are thus annealed during the 

 ordinary work of the furnace, that they may bo introduced into the muffle when ife 

 is brought into its proper degree of heat. A little above this gallery is a door,/, by 

 which, if thought proper, the charcoal could be introduced into the furnace ; above 

 that there is placed, at g, a throttle-valve, which is used for regulating the draught 

 of the furnace at pleasure. Messrs. Anfrye and D'Arcet say, that, to give the furnace 

 the necessary degree of heat so as to work assays of gold, the tube must be about 

 18 inches above the gallery for annealing or heating the cupels. The circular opening 

 in the dome, h (fy. 1829, and as seen in section/^. 1830), is used to introduce the 

 charcoal into the furnace : it is also used to inspect the interior of the furnace, and to 

 arrange the charcoal round the nnifflo. This opening is kept shut during the work- 

 ing of the furnace, with the mouth-piece, of which the face is seen at n.fig. 1830. 



The section of the furnace, fig. 1 830, presents several openings, the principal of which 

 is that of the muffle ; it is placed at i ; it is shut with the semicircular door m, fig. 1 829, 

 and seen in the section m,fig. 1830. In front of this opening, is the table or shelf 

 upon which the door of the muffle is made to advance or recede. The letter q, fig. 

 1830, shows the face, side, and cross-section of the shelf, which makes part of the fur- 

 nace. Immediately under the shelf is a horizontal slit, I, which is pierced at the level 

 of the upper part of the grate, and used for the introduction of a slender rod of iron, 

 that the grate may be easily kept clean. This opening is shut at pleasure, by the 

 wedge represented at k,figs. 1829 and 1830. 



Upon the back of the furnace is a horizontal slit, p, fig. 1830, which supports the 

 fire-brick, s, and upon which the end of the muffle, if necessary, may rest ; u, fig. 1830, 

 is the opening in the furnace where the muffle is placed. 



The plan of the grate of the furnace is an ellipse : fig. 1832 is a horizontal view of 

 it. The dimensions of that ellipsis determine the general form of the furnace, and 

 thickness of the grate. To give strength and solidity to the grate, it is encircled by 

 a bar or hoop of iron. There is a groove in which the hoop of iron is fixed. The 

 holes of the grate are truncated cones, having the greater base below, that the ashes 

 may more easily fall into the ash-pit. The letter v, fig. 1830, shows the form of these 

 holes. The grate is supported by a small bank or shelf, making part of the furnace, 

 as seen at a, fig. 1830. 



The ash-pit, c, has an opening, y, in front, fig. 1830; and is shut when necessary 

 by the mouth-piece, r,figs. 1829 and 1830. 



To give strength and solidity to the furnace, it is bound with hoops of irou, at 

 bbbb,fig. 1829. 



Figs. 1833, 1834, 1835, are views of the muffle. 

 Fig. 1836 is a view of a crucible for annealing gold. 



Figs. 1837, 1838, 1839, are cupels of various sizes, to be used in the furnace. They 

 are the same as those used by assayers in their ordinary furnaces. 



Figs. 1840 and 1841 are views of the hand-shovels, used for filling the furnace with 

 charcoal ; they should be made of such size and form as to fit the opening h, in figs. 

 1829 and 1830. 



The smaller pincers or tongs, by which the assays are charged into the cupels, and 

 by which the latter are withdrawn from the furnace, as well as the teaser for cleansing 

 the grate of the furnace, are similar to those used at the British Mint. (See MINT.) 



Cupel-mould; Cupels. The cupels used in the assay process are made of the ashes of 

 burnt bones (phosphate of lime). The cupels are formed in a cupel -mould made of 

 cast steel, very nicely turned, by which means they are easily freed from the mould 

 when struck. The bone-ash is used moistened with a quantity of water, sufficient to 

 make the particles adhere firmly together. The circular mould is filled, and pressed 

 level with its surface ; after which, a pestle or plug, having its end nicely turned, of a 

 convex shape, and of a size equal to the degree of concavity wished to bo made in the 

 cupel for the reception of the assay, is placed upon the ashes in the mould, and struck 

 with a mallet until the cupel is properly formed. These cupels are allowed to dry in 

 the air for some time before they are used. 



The assay by cupellation may be conducted as follows : 



We begin this assay process by weighing, in a delicate balance, a certain weight of 

 the metallic alloy ; a gramme ( = 16'432 gr.) is usually taken in France, and 10 or 12 

 grains in this country. The weight is wrapped up in a slip of lead-foil or paper, 

 should it consist of several fragments ; and there is added to it the proportion of lead 

 suitable to the quality of alloy to be assayed ; there being less lead, the finer tho 

 silver is presumed to be. Those who are much in tho habit of cupellation can make 

 good guesses in this way. If too much lead be xtsed for tho proportion of baser metal 

 present, a portion of the silver is wasted ; but if too little, then the whole of tho cop- 

 per is not carried off, and tho button of fine silver remains more or less impure. Tho 



