There is a principle underlying many of the phenomena of dry silver
assaying which the student should endeavour to understand; and which
serves to emphasise and explain some facts which without an explanation
may present difficulties. If a button of melted lead be covered with a
layer of slag rich in oxide of lead, and a second metal be added, this
other metal distributes itself between the metal and slag in proportions
which depend mainly upon the ease with which it is oxidised, and to a
large extent upon the relative quantities of material present. Easily
oxidisable metals such as zinc, iron, antimony and tin, will go mainly
into the slag, and, if the proportion of the slag is large, very little
will go into the metal. On the other hand, with metals oxidisable with
difficulty, such as silver, gold, and platinum, the reverse holds true;
nearly the whole of the metals will go into the lead, and very little
into the slag. If, however, the slag be very rich, say in antimony, the
lead will contain antimony; and, on the other hand, if the lead be very
rich in silver, the slag will contain silver in appreciable quantity.
Copper, which is near lead in the facility with which it is oxidised,
will serve for the purpose of a detailed example. The results of actual
analyses of metal and slag formed in contact with each other are shown
in the following table:--
---------------------------+--------------------------
Percentage Composition | Percentage Composition
of the Metal.
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