CUPELLING. "7 



the more borax. The ingredients should be well mixed 

 together and a little borax placed on the top. The crucible 

 should be heated, though not too rapidly at first, until 

 the contents are quite liquid. This will take about twenty 

 minutes. After which it may be removed and the contents 

 poured into the iron mould. When cool, the lead button 

 should be detached from the slag, cleaned, and beaten into 

 the shape of a cube ; it is then ready for cupellation. 



Fusion for silver and gold bearing copper ores and 

 sulphides. Weigh the ore and roast it before fusion is 

 commenced : 



Charge Ore . . . 100 to 500 grains. 



Red lead . . . 1000 



Charcoal powder . . . 35 

 Carbonate of soda 200 to 3000 



Borax . . . 150 to 300 



Cupelling. 



While the muffle is in the process of heating, place the 

 empty cupel (to make which see page 119) inside, and 

 when the proper temperature of the furnace is reached, 

 known by the cherry-red colour, gently, by means of the 

 cupel-tongs, place the lead button (containing the gold and 

 silver) obtained from the scorification or " fusion in the 

 crucible" method into the concave hollow of the bone-ash 

 cupel. Close the door of the muffle until the temperature 

 of the fused metal is the same as that of the muffle. The 

 behaviour of the assay can be observed through a slit at 

 the side or top of the door. The assay must not be allowed 

 to "freeze" ("freezing" is known by the fumes ascending 

 right to the top of the muffle), nor must it be too hot 

 (being too hot is known by the fumes scarcely rising at all, 

 and the outline of the cupel being indistinct). If inclined 

 to " freeze," a piece of charcoal may be put into the muffle 

 to increase the heat, and the fire stirred. When the proper 

 temperature is attained, the fumes from the cupel should 

 reach about half-way up the height of the t muffle, the cupel 

 should be red, and the metal very luminous, while a stream 

 of fused matter circulates about on the surface of the molten 



