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MERCURY. 243

all ortlilKU"^• tcnipcniUires. it is soluble in dilute nitric acid
and hot sulphuric; insoluble in hydrochloric acid.
Mercurv unites more or less readily with all the metals
excepting- iron and platinum; the latter metal will unite,
however, in the spongy condition. After this union of
mercury with another metal has taken place it is known
as an amalgam.
Fusing Point.—]\lercury fuses at 40° below zero, F.
^
Above this temperature it is fluid ; it boils at 660° F.
Compounds.— JVith Oxygen mercury unites to form
two classes of compounds, mercuric and mercurous oxids,
both of which are highly poisonous. IVitli Clilorin it
forms two compounds, mercuric chlorid (corrosive subli-
mate) and mercurous chlorid, familiarly known as calomel.
With lodin it forms two compounds, mercuric iodid and
mercurous iodid. JJlth SulpJuir, it combines to form sul-
phates and sulphids.
Vermilion, or mercuric sulphid, HgS, is a compound of
mercury extensively used in coloring vulcanisable rubbers
and celluloid. This is manufactured by heating in suitable
receptacles, mercury four parts with fine flowers of sulphur
one part.
Detection of Impurities.—Commercial mercury is never
quite pure, being more or less contaminated with lead, tin,
zinc, etc. A trace of these is contained in the metal as it
is made, but unscrupulous dealers frecjuently add base metals
to increase their profits, as a considerable amount of such
adulteration can take place without interfering with its
fluidity.
To detect the presence of foreign metals, allow a large
globule of the suspected sample to roll over the surface of a
sheet of white paper, when, if the metal is impure, it will
leave a streak of dross in its track, which will not occur
when it is absolutely pure.