Among the causes of the absorption losses of precious metals by the cupel, the distribution coefficient of these metals between the molten lead and litharge plays the most important role. From this point cf view it was argued that, when gold or silver exists alone, the rate of absorption is to be expressed by
Klog
e (1+x/a) where
Kis the distribution coefficient and x and a denote the amounts of lead and gold (or silver) expressed in atomic ratios. The theoretical presumptions were confirn ed not only by cupelling different weighs of gold or silver with lead under similar conditions and assaying the cupels, but also by interupting the process at various stages and determining the amount of gold or silver absorbed by that time. The rate of absorption of gold is ahout one fifth of that of silver and the distribution coeffients are 0.00057 and 0.0040 for gold and silver respectively.
The vari at. on in the rate of absorption of gold and silver by the coexistence of each other is to be explained likewise by the dilution of one metal by the other. Hitherto, the protective action of silver upon gold has often I een discussed by other authors and the present writer observed in addition that of gold upon silver and the effect was perceived to be of the same order when atomic ratio was taken into account.
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