OF THE ELEMENTARY BODIES. 247 
at a high temperature certainly requires a high temperature for 
its inflammation, and a continued external application of heat to 
support its combustion, whilst that reduced by potassium, when 
heated to a certain point, quickly burns into tantalic acid; but 
these differences may depend on mechanical causes. 
However, both tantalic acid and chloride of tantalum, accord- 
ing to Wohler’s experiments, have isomeric conditions, which 
correspond exactly with those of oxide of chromium and titanic 
acid, and allow of the supposition that the radical possesses cor- 
responding allotropic modifications. 
Uranium, reduced from the chloride by potassium, is one of 
the most combustible of the ‘elementary bodies; it dissolves in 
diluted acids with violence, hydrogen being evolved. If we 
compare this condition with that which Richter ascribes to the 
regulus which he reduced from the oxide of uranium by heating 
it with dried and powdered ox-blood in a forge for an hour and 
a half, which certainly was not pure uranium, but still consisted 
principally of it, dissolved completely in nitromuriatic acid, but 
was scarcely affected by hydrochloric acid, we have the counter- 
part in allotropic state of the two isomeric modifications of the 
soluble and insoluble protoxide of uranium. 
As regards the soft metals, it is more difficult to point out 
corresponding relations ; however, there are some which deserve 
attention. 
Tin, which in many points resembles titanium, has an oxide, 
which is isomorphous with titanic acid, and occurs in exactly 
the same two isomeric modifications. If we suppose these, in 
titanic acid, to depend upon dissimilar allotropic conditions of 
the radical, the same must also be the case with oxide of tin, or, 
as it is usually called, stannic acid. 
Iridium and osmium, when artificially reduced, cannot be ob- 
tained of that high specific gravity which they possess when oc- 
curring in the mineral kingdom, nor in that state of indifference 
to reagents, which exists to such an extent that they cannot be 
made to combine with other metals in a state of fusion at a white 
heat, but separate with their continuity and form unaltered 
when the metal is dissolved. We can no more convert them 
artificially into this allotropic condition than we can transform 
charcoal into diamond. 
But osmium, in the form in which we obtain it in the labora- 
tory, burns readily on the application of heat, forming a volatile 
