able lustre. It is hard, and not easily cut with a knife. The specific gravity is nearly 7.2 The ores of zinc are calamine and blende. See CALAMINARIS. Calamine is an oxide, frequently with a portion of carbonic acid; blende is a sulphuret, containing also some iron, and other extraneous matters. The ores of zinc are

found in many countries, and in a number of mines in this country. The metal is obtained from the ore by distillation.

Zinc is melted by a moderate heat, and the fused mass, on cooling, forms regular crystals. Though scarcely altered by exposure to the air at a low temperature, yet it is rapidly oxydized by one amounting to ignition. When kept in a degree of heat barely sufficient for its fusion, zinc becomes covered with a grey oxide. But when thrown into a crucible, or deep earthen pot, heated to whiteness, it suddenly inflames, burns with a beautiful white flame, and a white and light oxide sublimes, having a considerable resemblance to carded wool. This oxide, how

ever, when once deposited, is no longer volatile; but if exposed to a violent heat, runs into glass. Zinc readily dissolves in sulphuric, nitric, and muriatic acids. With nitric acid, it yields nitrous gas, if the acid be concentrated; or nitrous oxide,

if diluted. Sulphuric and muriatic acids,

diluted with water, evolve, during their action on this metal, hydrogen gas; and the gas, when obtained, holds in combination a portion of the metal. A stream of it has been found, if recently prepared, to occasion the fusion of the platina wire, though the pure gas is destitute of this property. This hydrogen gas, holding zinc in solution, may also be obtained by a process of Vauquelin. A mixture of the ore of zinc, called blende or calamine, with charcoal, is to be put into a porcelain tube, which is to be placed horizontally in a furnace, and, when red-hot, the vapour of water is to be driven over it. The gas that is produced, however, is a mixture of carbonic acid, carburetted hydrogen, and hydro-zincic gas. The zinc is deposited on the surface of the water, by which this gas is confined, but, if burned when recently prepared, the gas exhibits, in consequence of this impregnation, a blue flame. The solution of zinc in sulphuric acid shoots into regular crystals. This salt is readily soluble, and its solution is not precipitated by any other metal. The muriate of zinc yields, when evaporated, an extract of thick consistence, having the viscidity of birdlime. Zinc is oxydized also, when boiled

with solutions of pure alkalies; and a portion of the oxide is retained in solution. It is oxydized when mixed with nitre, and projected into a red-hot crucible. In this case a violent detonation ensues.

Zinc combines with almost all the metals, and some of its alloys are of great importance. It may be united to gold in any proportion by fusion. The alloy is the whiter and the more brittle, the greater quantity of zinc it contains. An metals, is very hard and white, receives a alloy, consisting of equal parts of these fine polish, and does not tarnish readily. It has therefore been proposed as very One part of zinc is said to destroy the proper for the specula of telescopes. ductility of one hundred parts of gold. The alloy is brittle, pretty hard, very Platinum combines very readily with zinc. fusible, of a bluish-white colour, and not so clear as that of zinc. The alloy of silver and zinc is easily produced by fusion. It is brittle, and has not been apwith mercury, either by triturating the plied to any use. Zinc may be combined two metals together, or by dropping mer cury into melted zinc. This amalgam is solid. It crystallizes when melted, and cooled slowly into lamellated hexagonal figures with cavities between them. They

are composed of one part of zinc, and two and a half of mercury It is used to rub on electrical machines, in order to excite electricity.

Zinc combines readily with copper, and forms one of the most useful of all the metallic alloys. The metals are usually combined together by stratifying plates of copper, and a native oxide of zinc combined with carbonic acid, called calamine, and applying heat. When the zinc does not exceed a fourth part of the copper, the alloy is known by the name of brass. It is of a beautiful yellow colour, more fusible than copper, and not so apt to tarnish. It is malleable, and so ductile, that it may be drawn out into wire. Its density is greater than the mean. It ought to be by calculation 7.6, but it actually is 8.4. nearly, so that its density is increased by about one-tenth. When the alloy contains three parts of zinc and four of copper, it assumes a colour nearly the same with gold, but it is not so malleable as brass. It is then called pinchbeck, prince's metal, or Prince Rupert's metal. Brass was known, and very much valued by the an cients. They used an ore of zinc to form it, which they called cadmia. Dr. Watson has proved that it was to brass that

they gave the name of orichalcum. Their æs was copper, or rather bronze.

It is very difficult to form an alloy of iron and zinc. Malouin has shown that zinc may be used instead of tin to cover iron plates, a proof that there is an affinity between the two metals. Tin and zinc may be easily combined by fusion. The alloy is much harder than zinc, and scarcely less ductile. This alloy is often the principal ingredient in the compound called pewter.

ZINNIA, in botany, so named in honour of John Godofr. Zinn, a genus of the Syngenesia Polygamia Superflua class and order. Natural order of Composite Oppositifolia. Corymbiferæ, Jussieu. Essential character: calyx ovate, cylindrical, imbricate; florets of the ray five, permanent, entire; seed down, with two erect awns; receptacle chaffy. There are five species.

ZIRCON, in mineralogy, the name of a genus containing two species, viz. hyacinth and zircon: the former will be found in the alphabetical arrangement; we therefore proceed to the species zircon, the chief colour of which is grey; but it occurs through all the varieties of green, blue, red, yellow, and brown. It is found commonly in roundish angular pieces, which have almost always rounded angles and edges. It is likewise crystallized. Specific gravity about 4.6. The constituent parts are, according to Klaproth, Zirconia Silica Oxide of iron Loss

69.0

26.5

0.5

4.0

100.0

It is infusible without addition by the blow-pipe; with borax it forms a colourless glass. It is found in Ceylon, in the sand of a river, accompanied by crystals of spinelle, tourmaline, ceylanite. It is also found in America; Mr. Solomon Conrad of Philadelphia discovered it near

Trenton, New Jersey. It is frequently cut as a precious stone, and employed for various purposes, particularly as an ornament in mourning-dress. When it is cut it exhibits, though in a very faint degree, the play of colours of the diamond. Some of the varieties are frequently used by watchmakers in jewelling watches. ZIZANIA, in botany, a genus of the

Monoecia Hexandria class and order. Natural order of Gramina. Gramineæ, Jussieu. Essential character: male, calyx

none; corolla glume two-valved, awnless, mixed with the females; female, calyx none; corolla glume two-valved, cowled, awned; style two-parted; seed one, clothed with the plaited corolla. There are two species; viz. Z. aquatica, and Z. terrestris.

ZIZIPHORA, in botany, a genus of the Diandria Monogynia class and order. Natural order of Verticillatæ. Labiatæ, Jussieu. Essential character; calyx fili. form; corolla ringent, with the upper lip bent back and entire; seeds four. There are four species.

ZODIAC, in astronomy, a broad circle, whose middle is the ecliptic, and its extremes, two circles, parallel thereto, at such a distance from it, as to bound or comprehend the excursions of the sun and planets.

The sun never deviates from the middle of the zodiac, i. e. from the ecliptic, but the planets all do more or less. Their greatest deviations, called latitudes, are the measure of the breadth of the zodiac, which is broader or narrower, as the greatest latitude of the planets is made more or less; accordingly some make it sixteen, some eighteen, and some twenty degrees broad. The zodiac, cutting the equator obliquely, makes an angle therewith of about 234°, which is what we call the obliquity of the zodiac, and is the sun's greatest declination.

The zodiac is divided into twelve portions, called signs, and those divisions or signs are denominated from the constel. lations which anciently possessed each part but the zodiac being immoveable, and the stars having a motion from west to east, those constellations no longer correspond to their proper signs, whence arises what we call the precession of the equinoxes.

ZOEGEA, in botany, a genus of the and order. Natural order of Composite Syngenesia Polygamia Frustranea class Capitatæ. Cinarocephala, Jussieu. Essential character; calyx imbricate; coroled; receptacle bristly. There is but one la of the ray ligulate; down bristle-shapspecies, viz. Z. leptaurea, a native of the Levant.

ZOISITE, in mineralogy, is of a greyish colour. It occurs massive, and in crystals, which are imbedded. It occurs in primitive mountains, principally in quartz with mica. This fossil is placed between the axinite and pistazite, and connects both species together.

ZONE, in geography and astronomy,

Its

a division of the terraqueous globe, with respect to the different degrees of heat found in the different parts thereof. A zone is the fifth part of the surface of the earth, contained between two parallels. The zones are denominated torrid, frigid, and temperate. The torrid zone is a band surrounding the terraqueous globe, and terminated by the two tropics. breadth is 46° 58'. The equator running through the middle of it, divides it into two equal parts, each containing 23° 29'. The ancients imagined the torrid zone uninhabitable. The temperate zones are two bands, environing the globe, and contained between the tropics and the polar circles: the breadth of each is 43° 2′. The frigid zones are segments of the surface of the earth, terminated, one by the antarctic, and the other by the arctic circle. The breadth of each is 46° 58'.

ZONITES, in natural history, a genus of insects of the order Coleoptera: antennæ testaceous; four feelers filiform; jaw entire, longer than the feelers; lip emarginate. There are eight species, found chiefly in warm countries.

ZOOLOGY, constitutes that branch of natural history which relates to animals. Various methods of arrangement have, by different naturalists, been devised to render this branch of study easy of comprehension, and familiar to the minds of those who wish for a general view of animated nature. We shall, in this article, give an outline of the Linnæan system, which has, in the various departments of the British Encyclopedia, been adopted, as most generally approved by philosophers of all countries.

Linnæus divides the whole animal king'dom into six classes, the characters of which are taken from the internal structure of the being treated of. It may be observed, that a considerable portion of the bulk of animals is composed of tubu lar vessels, which originate in a heart: the heart propels through the arteries, with the assistance of their own muscular powers, either a colourless transparent fluid, or a red blood, into the extremities of the veins; through which it again returns to the origin of motion. Insects and worms have their circulating fluids a little warmer than the surrounding medium, and in general it is colourless; but insects have legs furnished with joints, and worms have nothing but simple tentacula at most, in place of legs. Fishes have cold red blood, which is exposed to the air contained in water by means of their gills. Amphibia receive

the air into their lungs, but their blood is likewise cold, and in both fishes and amphibia the heart has only two regular cavities, while that of animals with warm blood has four. Of the latter, the oviparous are birds, and are generally covered with feathers; the viparous are either quadrupeds or cetaceous animals, and are furnished with organs for suckling their young. See PHYSIOLOGY.

Each of the classes of animals is subdivided by Linnæus into different orders: for a scientific account of these orders, and also of the classes from whence they spring, the reader is referred to the several heads of the Dictionary in the alphabetical order: and here we shall take a cursory view of the subject, in order to give, in a short compass, a sort of outline of the science.

The first class, denominated Mammalia, from the female's suckling its young, comprehends all viviparous animals with warm blood. These, with very few exceptions, have teeth fixed in their jawbones; and from the form and number of these teeth the orders are distinguished, except that of cetaceous fishes, which is known by the fins that are found in the place of feet. The distinctions of the teeth are somewhat minute, but they appear to be connected with the mode of life of the animal, and they are tolerably natural. The first order, Primates, contains man, monkeys, and bats: the second, Bruta; among others, the elephant, the rhinoceros, the ant-eater, and the ornithorynchus, an extraordinary quadruped, lately discovered in New Holland, with a bill like a duck, and sometimes teeth inserted behind it: but there are some suspicions that the animal is oviparous. The order Feræ contains the seal, the dog, the cat, the lion, the tiger, the weasel, and the mole, most of them beasts of prey; the opossum and the kangaroo also belong to this order, and the kangaroo feeds on vegetables, although its teeth are like those of carnivorous animals. The fourth order, Glires, comprehends beavers, mice, squirrels, and hares: the fifth, Pecora, camels, goats, sheep, and horned cattle. The sixth order, Belluæ, contains the horse, the hippopotamus, and the hog. The cetaceous fishes, or whales, form the seventh and last order; they reside in the water, enveloped in a thick clothing of fat, that is, of oily matter, deposited in cells, which enables their blood to retain its temperature, notwithstanding the ex ternal contact of a dense medium consi. derably colder.

Birds are distinguished from quadru peds by their laying eggs; they are also generally feathered, although some few are rather hairy, and, instead of hands or fore-legs, they have wings. Their eggs are covered by a calcareous shell; and they consist of a white, or albumen, which nourishes the chick during incubation, and a yolk, which is so suspended within it, as to preserve the side on which the little rudiment of a chicken is situa ted continually uppermost, and next to the mother that is sitting on it. The yolk is, in great measure, received into the abdomen of the chicken a little before the time of its being hatched, and serves for its support, like the milk of a quadruped, and like the cotyledons of young plants, until the system is become sufficiently strong for extracting its own food out of the ordinary nutriment of the species.

Birds are divided, according to the form of their bills, into six orders: Accipitres; as eagles, vultures, and hawks. Picæ; as crows, jackdaws, humming birds, and parrots. Anseres; as ducks, swans, and gulls. Gralla; as herons, woodcocks, and ostriches. Gallinæ; as peacocks, pheasants, turkies, and common fowls. And, lastly, Passeres; comprehending sparrows, larks, swallows, thrushes, and doves. The amphibia are in some respects very nearly allied to birds; but their blood is little warmer than the surrounding medium. Their respiration is not necessarily performed in a continual succession of alternations, since the whole of their blood does not pass through the lungs, and the circulation may continue without interruption in other parts, although it may be impeded in these organs for want of the motion of respiration. They are very tenacious of life; it has been asserted on good authority, that some of them have lived many years without food, inclosed in hollow trees, and even in the middle of stones: and they often retain vestiges of life some days after the loss of their hearts. Their eggs are generally covered with a membrane only. They have sometimes an intermediate stage of existence, in which all their parts are not yet developed, as we observe in the tadpole; and in this respect they resemble the class of insects. They are now universally considered as divided into two orders only: Reptilia; as the tortoise, the dragon, or flying lizard, the frog, and the toad; all these have four feet; but the animals which belong to the order Serpentes are without feet. Most of the serpentes are perfectly inno

1

cent, but others have fangs, by which they instil a poisonous fluid into the wounds that they make. In England, the viper is the only venomous serpent; it is known by its dark brown colour, and by a stripe of whitish spots running along its back: but to mankind its bite is seldom, if ever, fatal.

The first three classes of animals have lungs, as we have already seen, for respiration, and receive air by the mouth; those which have gills, and red blood, are fishes, residing either in fresh or in salt water, or indifferently in both: their eggs are involved in a membrane, and have no albumen.

Of the six orders of fishes, four have regular gills, supported by little bones; and they are distinguished according to the place of their ventral fins, into Apodes, as the eel and lamprey: Jugulares, as the cod: Thoracici, as the sole and perch: and Abdominales, as the salmon and pike: distinctions which appear to be perfectly artificial, although useful in a systematic arrangement. The two remaining orders are without bones in the gills, those of the one being soft, and of the other cartilaginous or gristly. These are, the Branchiostegi and Chondropterygii of Artedi, which Linnæus, from a mistake, classed among the Amphibia. The sun fish, the lump fish, the fishing frog, and the seahorse, are of the former; and the sturgeon, the skate, and the shark of the latter order.

Insects derive their name from being almost always divided, into a head, thorox, and abdomen, with very slender intervening portions: although these divisions do not exist in all insects. They are usually oviparous; they respire, but not by the mouth; they have a number of little orifices on each side of the abdomen, by which the air is received into their ramified trachea; and if these are stopped with oil, they are suffocated. Instead of bones, they have a hard integument or shell. Their mouths are formed on constructions extremely various, but generally very complicated: Fabricius has made these parts the basis of his classification; but from their minuteness in most species, the method is, in practice, insuperably inconvenient and the only way in which such characters can be rendered really useful is, when they are employed in the subdivisions of the genera, as determined from more conspicuous distinctions. Insects have most frequently jaws, and often several pairs, but they are always so placed as to open laterally or horizon

tally. Sometimes, instead of jaws, they have a trunk or proboscis. In general they pass through four stages of existence, the egg, the larva, or stage of growth, the pupa, or chrysalis, which is usually in a state of torpor or complete inactivity, and the imago, or perfect insect, in its nuptial capacity. After the last change, the insect most frequently takes no food till its death.

The Linnæan orders of insects are, the Coleoptera, with hard sheaths to their wings, generally called beetles; the Hemiptera, of which the sheaths are of a softer nature, and cross each other, as grasshoppers, bugs, and plant lice; the Lepidoptera, with dusty scales on their wings, as butterflies and moths; the Neuroptera, as the libellula, or dragon-fly, the may-fly, and other insects with four transparent wings, but without stings; the Hymenoptera, which have stings, either poisonous or not, as bees, wasps, and ichneumons; the Diptera with two wings, as common flies and gnats, which have halteres, or balancing rods, instead of the second pair of wings; and, lastly, the Aptera, without any wings, which form the seventh order, comprehending crabs, lobsters, shrimps, and prawns, for these are properly insects; spiders,scorpions, mille pedes, centipedes, mites, and monoculi. The Monoculus is a genus including the little active insects found in pond-water, which are scarcely visible to the naked eye, as well as the Molucca crab, which is the largest of all insects, being sometimes six feet long. Besides these, there are several genera of apterous insects, which are parasitical, and infest the human race as well as other animals.

The Vermes are the last and lowest of animated beings, yet some of them are not deficient either in magnitude or in beauty. The most natural division of vermes is into five orders; the Intestina, as earthworms and ascarides, which are distinguished by the want of moveable appendages, or tentacula, from the Mollusca, such as the dew snail, the cuttle fish, the sea anemone, and the hydra, or fresh water polype. The Testacea have shells of one or more pieces, and most of them inhabit the sea, and are called shell fish, as the limpet, the periwinkle, the snail, the muscle, the oyster, and the barnacle. The order Zoophyta contains corallines, sponges, and other compound animals, united by a common habitation, which has the general appearance of a vegetable, although of animal origin; each of the little inhabitants resembling a hydra, or

polype, imitating, by its extended arms, the appearance of an imperfect flower. The last order, Infusoria, is scarcely distinguished from the Intestina and Mollusca by any other character than the minuteness of the individuals belonging to it, and their spontaneous appearance in animal and vegetable infusions, where we can discover no traces of the manner in which they are produced. The process by which their numbers are sometimes increased is no less astonishing than their first production; for several of the genera often appear to divide, spontaneously, into two or more parts, which become new and distinct animals, so that in such a case the question respecting the identity of an individual would be very difficult to determine. The volvox, and some of the vorticella, are remarkable for their continual rotatory motion, probably intended for the purpose of straining their food out of the water: while some other species of the vorticella resemble fungi or corallines in miniature.

ZOOPHYTA, in natural history, an order of the class Vermes. Zoophyta are composite animals, holding a medium between animals and vegetables. Most of them take root and grow up into stems, multiplying life in their branches and deciduous buds, and in the transformation of their animated branches or polypes, which are endowed with spontaneous motion. Plants, therefore, resemble zoophyta, but are destitute of animation and the power of locomotion; and zoophyta are, as it were, plants, but furnished with sensation and the organs of spontaneous motion. Of these some are soft and naked, and others are covered with a hard shell: the former are by some naturalists called zoophytes, and the latter are denominated lithophytes. There are fifteen genera,