Cupellation


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Related to Cupellation: fire assay

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.

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

References in periodicals archive ?
For example, gold is a metal which resists cupellation and is insoluble in aqua fortis; that is a distinct idea, for it gives the criteria or definition of "gold.
Thus, given the right experiences, we can infer one from another a posteriori Hence, contrary to our initial suggestion, Leibniz seems to have held that from the definition, "a metal which resists cupellation and is insoluble in aqua fortis," one may come to infer a posteriori certain other intelligible properties about the defined entity, for example, that it is the heaviest metal and the most malleable.
During cupellation, a large part of the lead and of the impurities such as copper, tin and other metals are oxidised and partly vapourised, partly absorbed into the pores of the cupel.
For example, copper, nickel, bismuth, sulphur, tellurium and selenium are oxidised with difficulty during cupellation, hence they tend to remain in the button and to increase its weight.
The facility would consist of three principal areas: a sample receiving, drying, and preparation room; a furnace or "fire room" for fusion and cupellation operations; and a robotics room for automated instrument analysis of samples.
Filled racks of test tubes are taken to the robotics room for chemical processing and atomic absorption spectrometry, while trays of crucibles are moved to the fire room for fusion and cupellation, which is done in conventional manual fashion.
This is done in two steps: scorification and fine cupellation.
Georgius Agricola (1494-1555), in the seventh book of his main work, De Re Metallica (1556), provided a description of a grain scale for weighing the silver grains produced in the cupellation process.
Cupellation or fire assaying has, for centuries, been the only method recognised worldwide for the exact measurement of gold content.
The trueness of gold analysis can be enhanced using calibration standards, thus making the results comparable to cupellation.