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 ?
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.
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.
This is done in two steps: scorification and fine cupellation. Firstly a cupel (1.7 cm diameter) of sifted bone ash is struck with a hammer in an iron cupel mold with its corresponding stamp.
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.
(1985) Cupellation: The oldest quantitative chemical 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. Large samples can be measured economically through a fully automated measurement run and completely unknown samples can be analysed.
Compared to cupellation, ED-XRFA is still in its infancy as a method for gold analysis and its specific performance features have only partially been investigated.