822 METALS. 



ward and even nearly with the exterior surface of the fur 

 nace. The fire is made within the furnace, below, around, 

 and above ; and after heating up, the cupel is put in the muffle 

 with the assay in its shallow cup-shaped cavity. It thus has 

 the heat of the furnace to fuse the assay, and the air at the 

 same time is drawn in over it through the large opening of 

 the riuffle. The oxygen of the atmosphere unites with the 

 lead of the assay, and produces an oxyd, which oxyd sinks 

 into the cupel, leaving the silver or gold behind. The com- 

 pletion of the process is at once known by the change of the 

 assay suddenly to a bright shining globule. 



In the cupellation of gold containing copper, lead is melted 

 with the assay. The lead on being fused in a draft of air oxy- 

 dizes, and also promotes the oxydation of the copper, and 

 both oxyds Jisappear in the pores of the cupel leaving the 

 gold behind, and the silver alloyed. with it. In this process 

 the gold is melted with three times its weight of silver, (a 

 quartation as it is termed, the gold being one part out of four 

 of the alloy,) in order by its diffusion to effect a more com. 

 plete removal of the silver as well as the contained copper. 

 The cupel is placed in the heated furnace, and the gold, sil- 

 ver, and lead, on the cupel ; the heat is continued until the 

 surface of the metal is quiet and bright, when the cupella- 

 tion is finished; the metal then is slowly cooled and re- 

 moved. The button obtained, after annealing it by bringing 

 it to a red heat, is rolled out into a thin plate and boiled in 

 strong nitric acid. This process is repeated two or three 

 times with a change of the acid each time, and the silver is 

 thus finally removed. At the United States mint, half a 

 gramme of the gold is submitted to assay. The assay-gold 

 and quartation -silver are wrapped in a sheet of lead weigh- 

 ing about ten times as much as the gold under assay. After 

 cupellation, the plate of gold and silver, loosely rolled into a 

 coil, is boiled for 20 minutes in 4£ oz. of nitric acid, of 20 to 

 22 Beaume ; the acid is then poured off and another por- 

 tion of stronger acid is added, about half the former quantity, 

 and boiled 10 minutes ; then the same again. The gold 

 thus purified is washed and exposed to a red heat, for the 

 purpose of drying and annealing it, and then weighed. 



Uses. The uses of gold are- well known ; and also that 

 it owes a great part of its value to its extreme malleability, 

 and the fact of its not tarnishing on exposure. Although a 

 costly metal, it is one of the cheapest means of ornament, 



