_Of Nickel._
Nickel is a semi-metal of a reddish cast, of great hardness, and always
magnetical; on which account it is supposed to contain iron, though
chemists have not yet been able to separate them.
The purest nickel was so infusible as not to run into a mass in the
strongest heat of a smith's forge; but then it was in some degree
malleable.
Concentrated acid of vitriol only corrodes nickel. Alkalies precipitate
it from its solution in the nitrous acid, and dissolve the precipitate.
It readily unites with sulphur.
Nickel is found either native or mineralized with several other metals,
especially with copper, when it is called _kupfer nickel_, or _false
copper_, being of a reddish or copper colour.
This semi-metal has not yet been applied to any use.
_Of Arsenic._
What is commonly called _arsenic_ is the calx of a semi-metal called the
_regulus of arsenic_. It is a white and brittle substance, expelled from
the ores of several metals by heat. It is then refined by a second
sublimation, and melted into the masses in which it is commonly sold.
This calx is soluble in about eighty times its weight of cold water, or
in fifteen times its weight of boiling water. It acts in many respects
like an acid, as it decomposes nitre by distillation, when the nitrous
acid flies off, and the _arsenical salt of Macquer_ remains behind.
When the calx of arsenic is distilled with sulphur, the vitriolic acid
flies off, and a substance of a yellow colour, called _orpiment_, is
produced. This appears to consist of sulphur and the regulus of arsenic;
part of the sulphur receiving pure air from the calx, to which it
communicates phlogiston; and thus the sulphur becomes converted into
vitriolic acid, while the arsenical calx is reduced, and combines with
the rest of the sulphur.
The combination of sulphur and arsenic, by melting them together, is of
a red colour, known by the name of _realgal_, or _realgar_. It is less
volatile than orpiment.
The solution of fixed alkali dissolves the calx of arsenic, and by means
of heat a brown tenacious mass is produced, and having also a
disagreeable smell, it is called _liver of arsenic_.
The regulus of arsenic is of a yellow colour, subject to tarnish or grow
black, by exposure to the air, very brittle, and of a laminated texture.
In close vessels it wholly sublimes, but burns with a small flame in
pure air.
Vitriolic acid has little action upon this semi-metal, except when hot;
but the nitrous acid acts readily upon it, and likewise dissolves the
calx, as does boiling marine acid, though it affects it very little when
cold.
Most of the metals unite with the regulus of arsenic.
Dephlogisticated marine acid converts the calx of arsenic into
_arsenical acid_ by giving it pure air.
The acid of arsenic acts more or less upon all metals, but the phenomena
do not appear to be of much importance.
The calx of acid is used in a variety of the arts, especially in the
manufactory of glass. Orpiment and realgar are used as pigments. Some
attempts have been made to introduce it into medicine, but being
dangerous, the experiments should be made with caution.
_Of Cobalt._
Cobalt is a semi-metal of a grey or steel colour, of a close-grained
fracture, more difficult of fusion than copper, not easily calcined. It
soon tarnishes in the air, but water has no effect upon it.
Cobalt, dissolved in _aqua regia_, makes an excellent sympathetic ink,
appearing green when held to the fire, and disappearing when cold,
unless it has been heated too much, when it burns the paper.
The calx of cobalt is of a deep blue colour, which, when fused, makes
the blue glass called _smalt_. The ore of cobalt, called _zaffre_, is
found in several parts of Europe, but chiefly in Saxony. As it is
commonly sold, it contains twice or thrice its weight of powder of
flints. The smalt is usually composed of one part of calcined cobalt,
fused with two parts of powder of flint and one of pot-ash.
The chief use of cobalt is for making smalt; but the powder and the
blue-stone used by laundresses is a preparation made by the Dutch of a
coarse kind of smalt.
_Of Zinc._
Zinc is a semi-metal of a bluish cast, brighter than lead, and so far
malleable as not to be broken by a hammer, though it cannot be much
extended. When broken by bending, it appears to consist of cubical
grains. If it be heated nearly to melting, it will be sufficiently
brittle to be pulverized. It melts long before ignition, and when it is
red hot, it burns with a dazzling white flame, and is calcined with
such rapidity, that its calx flies up in the form of white flowers,
called _flowers of zinc_, or _philosophical wool_. In a stronger heat
they become a clear yellow glass. Heated in close vessels, this metal
rises without decomposition, being the most volatile of all the metals
except the regulus of _arsenic_.
Zinc dissolved in diluted vitriolic acid, yields much inflammable air,
and has a residuum, which appears to be plumbago, and the liquor forms
crystals, called _white copperas_. This metals also yields inflammable
air when dissolved in the marine acid. Dissolved in the nitrous acid, it
yields dephlogisticated nitrous air, with very little proper nitrous
air.
The ore of zinc, called _calamine_, is generally of a white colour; and
the chief use of it is to unite it with copper, with which it makes
brass and other gold-coloured mixtures of metals. The calx and the salts
of this metal are occasionally used in medicine.