Cupellation

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Related to Cuppelation: fire assay, Pattinson process, Parkes process

cupellation

[‚kyü·pə′lā·shən]
(metallurgy)
Method using a cupel for assaying precious metals.
Process for refining gold and silver by alloying them with lead and then oxidizing the molten lead to separate the base metal from the precious metal.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Cupellation

 

oxidation melting of an alloy of lead with noble metals (gold and silver) to separate them in pure form. Cupellation is based on the fact that lead and other base metals are easily oxidized at high temperatures by atmospheric oxygen, whereas the noble metals are unchanged.

Cupellation is used in assaying to establish the purity of a sample (the content of the noble metals in their alloys). The process takes place in cupels, which are small cups made from a porous refractory material (bone ash, magnesite, and others), at a temperature of 850°-900°C. During cupellation, lead and other base metals are converted into molten oxides, which are absorbed by the cupel, whereas the noble metals remain on its surface as “beads.”

In metallurgy, cupellation is the operation of separating noble metals from argentiferous lead; it is carried out in reverberatory furnaces at a temperature of about 1000°C. Lead and base metals are oxidized by the oxygen blast. The mixture of oxides, in which lead oxide (PbO) predominates, is in liquid form and flows continuously from the surface of the melt into a receptacle. A gold-silver alloy that sometimes contains platinum metals is produced on the hearth of the furnace.

REFERENCES

Loskutov, F. M. Metallurgiia svintsa. Moscow, 1965.
Priborootbiranie i analiz blagorodnykh metallov. Edited by I. F. Barysh-nikov. Moscow, 1968.

V. L. BELOVA and IU. F. VAIMAN

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.