slightly increased after hammering; its specific heat is 0.0548
(R. Bunsen), it melts at 310-320 deg. C. and boils between 763-772 deg. C. (T.
Carnelley), forming a deep yellow vapour. The cadmium molecule, as shown by
determinations of the density of its vapour, is monatomic. The metal unites
with the majority of the heavy metals to form alloys; some of these, the
so-called fusible alloys, find a useful application from the fact that they
possess a low melting-point. It also forms amalgams with mercury, and on
this account has been employed in dentistry for the purpose of stopping (or
filling) [v.04 p.0931] teeth. The metal is quite permanent in dry air, but
in moist air it becomes coated with a superficial layer of the oxide; it
burns on heating to redness, forming a brown coloured oxide; and is readily
soluble in mineral acids with formation of the corresponding salts. Cadmium
vapour decomposes water at a red heat, with liberation of hydrogen, and
formation of the oxide of the metal.

Cadmium oxide, CdO, is a brown powder of specific gravity 6.5, which can be
prepared by heating the metal in air or in oxygen; or by ignition of the
nitrate or carbonate; by heating the metal to a white heat in a current of
oxygen it is obtained as a dark red crystalline sublimate. It does not melt
at a white heat, and is easily reduced to the metal by heating in a current
of hydrogen or with carbon. It is a basic oxide, dissolving readily in
acids, with the formation of salts, somewhat analogous to those of zinc.

Cadmium hydroxide, Cd(OH)_2, is obtained as a white precipitate by adding
potassium hydroxide to a solution of any soluble cadmium salt. It is
decomposed by heat into the oxide and water, and is soluble in ammonia but
not in excess of dilute potassium hydroxide; this latter property serves to
distinguish it from zinc hydroxide.

The chloride, CdCl_2, bromide, CdBr_2, and iodide, CdI_2, are also known,
cadmium iodide being sometimes used in photography, as it is one of the few
iodides which are soluble in alcohol. Cadmium chloride and iodide have been
shown to behave in an anomalous way in aqueous solution (W. Hittorf, _Pogg.
Ann._, 1859, 106, 513), probably owing to the formation of complex ions;
the abnormal behaviour apparently diminishing as the solution becomes more
and more dilute, until, at very high dilutions the salts are ionized in the
normal manner.

Cadmium sulphate, CdSO_4, is known in several hydrated forms; bei