uble in acids with the escape of
hydrogen, the solutions being colorless. Its salts, soluble in water,
are decomposed by ignition in free air. Its soluble neutral salts
change blue litmus paper to red. The salts, insoluble in water, are
readily dissolved in acids.

_Oxide of Cadmium_ (CdO).--This oxide is of a dark orange color. It
does not melt, and is not volatile, not even at a very high
temperature. Its hydrate is white, loses in the heat its hydratic
water, and absorbs carbonic acid from the air when it is kept in open
vessels.

Cadmium oxide is unaltered when exposed upon platinum wire in the
flame of oxidation. When heated upon charcoal in the flame of
reduction it disappears in a very short time, while the charcoal is
coated with a dark orange or yellow powder, the color of which is more
visible after it is cooled. The portions of this sublimate furthest
from the assay present a visible iridescent appearance. This reaction
of cadmium is so characteristic and sensitive that minerals (for
instance, calamine, carbonate of zinc) which contains from one to five
per cent. of carbonate of cadmium, will give a dark yellowish ring of
cadmium oxide, a little distance from the assay, after being exposed
for a few moments to the flame of reduction. This sublimate is more
visible when cold, and is produced some time previous to the reduction
of the zinc oxide. If a vapor of the latter should appear, it
indicates that it has been exposed too great a length of time to the
flame.

Borax dissolves a considerable quantity of cadmium oxide upon a
platinum wire to a clear yellow bead, which, when cold, is almost
colorless. If the bead is nearly saturated with the cadmium oxide, it
appears milk-white when intermittingly heated. If the bead is
completely saturated, it retains its opalescent appearance. Upon
charcoal, and in the flame of reduction, the bead intumesces, the
cadmium oxide becomes reduced to metal; this becomes volatilized and
re-oxidized, and sublimes upon the charcoal as the yellow cadmium
oxide.

In the oxidation flame, microcosmic salt dissolves a large quantity of
it to a clear bead, which, when highly saturated and while hot, is
yellowish colored, but colorless when cold. By complete saturation,
the bead is enamel-white when cold.

Upon charcoal, in the flame of reduction, the bead is slowly and only
partially reduced, a scanty sublimate being produced on the charcoal.
The addition of tin promotes the reduc