The useful metals cover almost the entire range of the metallic elements in the electrochemical series. This generalization of the chemist is the same as the metallurgist's statement that the metals have all degrees of reducibility. The sequel illustrates abundantly what we mean. Sodium stands near the very extreme of the electropositive end of the list, with an affinity for oxygen and chlorine so powerful that decomposition and isolation are effected only by the most energetic chemical or electrochemical means. At the other end of the series are gold, iridium, and platinum, with solution pressures so faint that they naturally retain the metallic state and can be forced to combine with only a limited number of the most electronegative nonmetallic elements. Simply heating any of their compounds throws out these latter metals ready to melt for the market.
The metals, in general, are won by heating and reducing under proper chemical influences, but there are important exceptions. The arrangement in metallurgical series, Table I, indicates the degree of reducibility of the various metals.
By heating compounds - if originally metallic, merely fuse
From oxide compounds, easily, by metallic iron or by hot carbon monoxide
Only by carbon at 1000° C, in absence of carbon dioxide
With nothing less than metallic aluminum at very high temperature
Only by electricity, in absence of free or unavailable electronegative elements