A Textbook Of Fire Assaying PDF Download

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1922 edition. Excerpt: ...or cupellation. In general it may be said that the metals in a molten alloy, such as a lead button on a cupel, or the lead alloy in a scorifier, are oxidized in succession, each partly protecting those which are less easily oxidized than itself. This separation is not quantitative however, owing to the effect of mass action, and in the case under discussion, where we have a large amount of lead and small amounts of other metals, a considerable amount of lead would be oxidized during the complete oxidation of the metals above it in the table. Those metals which lie below lead in the table will be but slowly slagged in scorification and only at the expense of a large amount of lead. Thus, during scorification or cupellation, bismuth, copper and tellurium are concentrated in the residual unoxidized lead and this explains why it is so difficult to separate these metals from silver by scorification and cupellation. This can only be done by repeated scorification with fresh lead and, as might be expected, this will result in a considerable loss of silver. From their positions in the table, it is evident that silver is not easily oxidized and that gold is protected by all other metals. To one who has a knowledge of the mineral character of the ore, a glance at the ignition temperature of the sulphides shown in Table XVI will afford an idea of the initial temperature required for scorification. From a comparison of the heats of oxidation of the metals present with that of lead, the relative ease or difficulty of their elimination in scorification may be determined; and a knowledge of the solubility of the metal oxides in litharge and in borax will indicate the relation between ore, lead and flux which will give the most satisfactory results. A...