ZAFFRE. See COBALT.
ZEDOARY, is the root of a plant which grows in Malabar, Ceylon, &c. It
occurs in wrinkled pieces, externally ash-coloured, internally
brownish-red; possessed of a fragrant odour, somewhat resembling
camphor; and of a pungent, aromatic, bitterish taste. It contains,
according to Bucholz, 1·42 of volatile oil, of a burning camphorated
taste; 3·60 of a soft, bitter, aromatic resin; 11·75 of a bitter
aromatic extract, mixed with a little resin and potash-salts; 4·5 of
gum; 9 of vegetable mucilage; 3·60 of starch; 8·0 of a starchy extract
from the woody fibre, by means of caustic potassa, along with 31·2 of
another matter, 12·89 of woody fibre, and 15 of water. According to
Morin, this root, contains besides, an azotized substance, analogous to
the extract of beef.
ZIMOME, is a principle supposed by Taddei to exist in the gluten of
wheat-flour. Its identity is not recognised by later chemists.
ZIRCON. See HYACINTH and LAPIDARY.
ZIRCONIA, is a rare earth, extracted from the minerals zircon and
hyacinth; it is an oxide of zirconium, a substance possessing externally
none of the metallic characters, but resembling rather charcoal powder,
which burns briskly, and almost with explosive violence.
ZINC, is a metal of a bluish-white colour, of considerable lustre when
broken across, but easily tarnished by the air; its fracture is hackly,
and foliated with small facets, irregularly set. It has little cohesion,
and breaks in thin plates before the hammer, unless it has been
previously subjected to a regulated process of lamination, at the
temperature of from 220° to 300° F., whereby it becomes malleable, and
retains its malleability and ductility afterwards. On this singular
property, a patent was taken out by Messrs. Hobson and Sylvester, of
Sheffield, many years ago, for manufacturing sheet zinc, for covering
the roofs of houses, and sheathing ships; but the low price of copper at
that time, and its superior tenacity, rendered their patent ineffective.
The specific gravity of zinc varies from 6·9 to 7·2, according to the
condensation it has received. It melts under a red heat, at about the
680th or 700th degree of Fahrenheit’s scale. When exposed to this heat
with contact of air, the metal takes fire, and burns with a brilliant
bluish-white light, while a few flocculi, of a woolly-looking white
matter, rise out of the crucible, and float in the air. The result of
the combustion is a white powder, formerly called flowers, but now oxide
of zinc; consisting of 34 of metal, and 8 of oxygen, being their
respective prime equivalents; or, in 100 parts, of 81 and 19.
The principal ores of zinc are, the sulphuret called _blende_, the
silicate called _calamine_ and the sparry calamine, or the carbonate.
1. _Blende_ crystallizes in the garnet-dodecahedron; its fracture is
highly conchoidal; lustre, adamantine; colours, black, brown, red,
yellow, and green; transparent or translucent; specific gravity, 4. It
is a simple sulphuret of the metal; and, therefore, consists, in its
pure state, of 34 of zinc, and 16 of sulphur. It dissolves in nitric
acid, with disengagement of sulphuretted hydrogen gas. It occurs in beds
and veins, accompanied chiefly by galena, iron pyrites, copper pyrites,
and heavy spar. There is a radiated variety found at Przibram,
remarkable for containing a large proportion of cadmium. Blende is found
in great quantities in Derbyshire and Cumberland, as also in Cornwall.
2. _Calamine_, or silicate of zinc, is divided into two species; the
prismatic or electric calamine, and the rhomboidal; though they both
agree in metallurgic treatment. The _first_ has a vitreous lustre,
inclining to pearly; colour, white, but occasionally blue, green,
yellow, or brown; spec. grav. 3·38. It often occurs massive, and in
botroidal shapes. This species is a compound of oxide of zinc with
silica and water; and its constituents are--zinc oxide, 66·37; silica,
26·23; water, 7·4; in 100 parts. Reduced to powder, it is soluble in
dilute sulphuric or nitric acid, and the solution gelatinizes on
cooling. It emits a green phosphorescent light before the blowpipe. The
second species, or rhombohedral calamine, is a carbonate of zinc. Its
specific gravity is 4·442, much denser than the preceding. It occurs in
kidney-shaped, botroidal, stalactitic, and other imitative shapes;
surface generally rough, composition columnar. Massive, with a granular
texture, sometimes impalpable; strongly coherent. According to
Smithson’s analysis, Derbyshire calamine consists of--oxide of zinc,
65·2; carbonic acid, 34·8; which coincides almost exactly with a prime
equivalent of the oxide and acid, or 42 + 22 = 64.
The mineral genus called _zinc-ore_, or red oxide of zinc, is denser
than either of the above, its spec. grav. being 5·432. It is a compound
of oxide of zinc 88, and oxide of iron and manganese 12. It is found
massive, of a granular texture, in large quantities, in several
localities, in New Jersey. It is set free in several metallurgic
processes, and occurs crystallized in six-sided prisms of a yellow
colour, in the smelting-works of Kœnigshutte in Silesia, according to
Mitscherlich.
The zinc ores of England, like those of France, Flanders, and Silesia,
occur in two geological localities.
The first is in veins in the carboniferous or mountain limestone. The
blende and the calamine most usually accompany the numerous veins of
galena which traverse that limestone; though there are many lead mines
that yield no calamine; and, on the other hand, there are veins of
calamine alone, as at Matlock, whence a very considerable quantity of
this ore is obtained.
In almost every point of England where that metalliferous limestone
appears, there are explorations for lead and zinc ores. The
neighbourhood of Alston-moor in Cumberland, of Castleton and Matlock in
Derbyshire, and the small metalliferous belt of Flintshire, are
peculiarly marked for their mineral riches. On the north side of the
last county, calamine is mined in a rich vein of galena at Holywell,
where it presents the singular appearance of occurring only in the
ramifications that the lead vein makes from east to west, and never in
those from north to south; while the blende, abundantly present in this
mine, is found indifferently in all directions.
The second locality of calamine is in the magnesian limestone formation
of the English geologists, the alpine limestone of the French, and the
zechstein of the Germans. The calamine is disseminated through it in
small contemporaneous veins, which, running in all directions, form the
appearance of a network. These veins have commonly a thickness of only a
few inches; but in certain cases they extend to four feet, in
consequence of the union of several small ones into a mass. The
explorations of calamine in the magnesian limestone, are situated
chiefly on the flanks of the Mendip Hills, a chain which extends in a
north-west and south-east direction, from the canal of Bristol to Frome.
The calamine is worked mostly in the parishes of Phipham and Roborough,
as also near Rickford and Broadfield-Doron, by means of a great
multitude of small shafts. The miners pay, for the privilege of working,
a tax of 1_l._ sterling per annum to the Lords of the Treasury; and they
sell the ores, mixed with a considerable quantity of carbonate of lime,
for 1_l._ per ton, at Phipham, after washing it slightly in a sieve.
They are despatched to Bristol, where they receive a new washing, in
order to separate the galena.