hat the importance of the
isomeric and allotropic states has been much neglected in the case of
metals. Joule and Lyon Playfair showed, in 1846, that metals in
different allotropic states possess different atomic volumes, and
Matthiessen, in 1860, was led to the view that in certain cases where
metals are alloyed they pass into allotropic states, probably the most
important generalization which has yet been made in connection with the
molecular constitution of alloys. Instances of allotropy in pure metals
are: Bolley's lead, which oxidizes readily in air; Schutzenberger's
copper; Fritsche' tin, which falls to powder when exposed to
exceptionally cold winter; Gore's antimony; Graham's palladium and
allotropic nickel. Joule has also proved that, when iron is released
from its amalgam by distilling away the mercury, the metallic iron takes
fire on exposure to air, and is therefore clearly different from
ordinary iron.

* * * * *

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