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soft and malleable, and from 200 to 300 grs. in weight ; larger buttons should be reduced 

 in -weight by rescorifying. The slag should bo free from small lumps, and perfectly 

 fused before pouring. All silver ores may be assayed by this method, and several 

 assays made at one time, but a fusion-method is preferable for ores poor in silver. 

 Where a number of assays are made by the scorification process, a muffle-furnace of 

 somewhat larger dimensions is constructed than that described under the Assaying of 

 Silver Alloys. With poor ores, four or more scorifiers are charged with weighed por- 

 tions of ore and lead, and the resulting buttons of lead reduced to one button by re- 

 peated seorification, and then finally cupelled. Correction must be made for the silver 

 contained in the amount of granulated lead employed. 



In England the results obtained from the assays are reported to ounces, penny, 

 weights, and grains troy, upon the statute ton of 2,240 Ibs. The calculations may 

 be made by the following Table : 



Table showing the weight of silver to the ton of ore or alloy corresponding to the weight 

 in grains obtained from 400 grains of the substance operated on. 



2. The Assaying of Silver and its Alloys. This is conducted by the dry and wet 

 methods. 



a. Dry Method by Cupellation (Coupellation, Fr. ; Abtreiben auf der Cupelle, Ger.). 

 The assay by this method is made iipon a cupel, and the process is conducted in a 

 cupellation-furnace, or a muffle-furnace. The art of assaying silver by the cupel is 

 founded upon the feeble affinity which this metal has for oxygen, in comparison with 

 lead and copper, and other metals ; and on the tendency which the latter metal has to 

 oxidise rapidly in contact with lead at a high temperature, and sink with it into any 

 porous earthy vessel in a thin glassy or vitriform state. The porous vessel may be 

 made either of wood-ashes, freed from their soluble matter by washing with water ; 

 or, preferably, of burned bones, or bone-ash, reduced to a fine powder. The cupels 

 allow the fused oxides to be absorbed into them like a sponge, but are impermeable to 

 the particles of metals ; and thus the former pass readily down into their substance, 

 while the latter remain upon their surface : a phenomenon owing to the circumstance 

 of the oxides moistening, as it were, the bone-ash powder, whereas the metals can 

 contract no adherence with it. Hence also the liquid metals preserve a hemispherical 

 shape in the cupels, as quicksilver does in a cup of glass, while the fused oxide spreads 

 over, and penetrates their substance, like water. 



If wo put into a cupel, therefore, two metals, of which the one is unalterable in the 

 air, the other susceptible of oxidisemeut, and of producing a very fusible oxide, it is 

 obvious that, by exposing both to a proper degree of heat, we shall succeed iu 

 separating them. We should also succeed, though the oxide were infusible, by placing 

 it in contact with another one, which may render it fusible. Iu both cases, however, 



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