continuity, and occasion the
alloy to become brittle. The alloys of mercury, with the other metals,
have usually been called _amalgams_, and we see no inconvenience from
continuing the use of that term.

Sulphur, phosphorus, and charcoal, readily unite with metals.
Combinations of sulphur with metals are usually named _pyrites_. Their
combinations with phosphorus and charcoal are either not yet named, or
have received new names only of late; so that we have not scrupled to
change them according to our principles. The combinations of metal and
sulphur we call _sulphurets_, those with phosphorus _phosphurets_, and
those formed with charcoal _carburets_. These denominations are extended
to all the combinations into which the above three substances enter,
without being previously oxygenated. Thus, the combination of sulphur
with potash, or fixed vegetable alkali, is called _sulphuret of potash_;
that which it forms with ammoniac, or volatile alkali, is termed
_sulphuret of ammoniac_.

Hydrogen is likewise capable of combining with many combustible
substances. In the state of gas, it dissolves charcoal, sulphur,
phosphorus, and several metals; we distinguish these combinations by the
terms, _carbonated hydrogen gas_, _sulphurated hydrogen gas_, and
_phosphorated hydrogen gas_. The sulphurated hydrogen gas was called
_hepatic air_ by former chemists, or _foetid air from sulphur_, by Mr
Scheele. The virtues of several mineral waters, and the foetid smell of
animal excrements, chiefly arise from the presence of this gas. The
phosphorated hydrogen gas is remarkable for the property, discovered by
Mr Gengembre, of taking fire spontaneously upon getting into contact
with atmospheric air, or, what is better, with oxygen gas. This gas has
a strong flavour, resembling that of putrid fish; and it is very
probable that the phosphorescent quality of fish, in the state of
putrefaction, arises from the escape of this species of gas. When
hydrogen and charcoal are combined together, without the intervention of
caloric, to bring the hydrogen into the state of gas, they form oil,
which is either fixed or volatile, according to the proportions of
hydrogen and charcoal in its composition. The chief difference between
fixed or fat oils drawn from vegetables by expression, and volatile or
essential oils, is, that the former contains an excess of charcoal,
which is separated when the oils are heated above the degree of boiling
water; whereas t