ZINC.

Symbol, Zn. Atomic weight, 65'2.

This metal, it is stated by Griffiths, "was first thus called in the writings of Paracelsus, about the year 1540. The term is probably derived from the German word zinken, signifying 'nails,' and applied to this metal on account of its frequently forming pointed particles somewhat resembling nails when melted and suddenly poured into water."

SOURCES WHENCE DERIVED.

It is obtained from the mines of Cornwall, Wales, Cumberland, and the Isle of Man, in the form of zincic sulphide (Blende or Black Jack), and zincic carbonate or calamine; is very abundant in England, and is found principally in the Mendip Hills and various parts of Somersetshire, at Holywell, Flintshire, at Castleton, Derbyshire, and in Cumberland.

In order to reduce the zincic sulphide or carbonate to the metallic state, the powdered ore is roasted or calcined, by which it loses about 20 per cent., and is converted into an oxide. It is then ground in a mill, and mixed with powdered coal, and strongly heated in large clay crucibles, so that, as the vapour of zinc is produced, it is distilled per descensum, and is condensed partly in powder and partly in irregular-shaped lumps, which fall into iron basins placed at the end of the pipe: this is constantly looked to, to prevent the zinc that distils over clogging it up. The crude metal is again melted and cast into ingots or sheets.

PHYSICAL PROPERTIES.

Zinc presents a beautiful crystalline structure if a thick bar or slab is broken with a sledge-hammer; its colour is a bluish-white. In bending zinc for battery purposes, it is soon found that if the metal is heated to about 300° F., it is much more manageable and does not break, and thus in rolling the zinc the slabs are always previously heated to 212° or 300°; at a higher temperature it again becomes brittle, and melts at 773° F.

The specific gravity of zinc is 6'8 to 7.1. The "Building News," speaking with authority on the application of this metal to building and other purposes,

says:

"This metal has been largely employed for pipes, for galvanic batteries used in working the electric telegraph, as a substitute for white lead, and as a constituent of brass and German silver.

"Zinc is, as is well known, largely obtained from Prussia; and we find that nearly 4,500,000 cwt. of zinc were obtained in 1857. In the seven large smelting establishments in Belgium and Prussia, belonging to the Vieille Montagne Company, there are 230 furnaces. Fifteen years ago the quantity of zinc used for roofing was not more than 5,000 tons; now, it appears, 23,000 tons of sheet zinc are annually made by this Company. For ship sheathing 3,500 tons are produced, although fifteen years ago zinc was not employed at all for this purpose. Stamped ornaments in zinc date only from 1852; now there are 1,500 tons produced for this object. For ships' sheathing zinc must necessarily be altogether free from impurity, or it will soon decay. But there can be no question about the usefulness of this metal for building purposes; and the fact that it is coming into still greater use and is becoming better known and appreciated is evidence that its reputation is increasing. With care in purchasing and laying there is but little doubt that it will turn out well. In Paris it has been used for nearly every roof formed for some years. The new markets, constructed of iron in 1856, have been covered with zinc, and, excepting in one place where the workmen were careless, the whole of the zinc is in capital condition. In Germany zinc for roofing is largely used, and the work is generally remarkable for solidity and closeness."

CHEMICAL PROPERTIES.

At a bright red heat and when exposed to the air zinc is rapidly oxidized, and then takes fire, burning with a bright greenish flame, and forming the only oxide of this metal, viz., the zincic oxide (ZnO), or what was formerly called the "flos philosophorum" or philosopher's wool, and now termed zinc white.

The chief salts of zinc are zincic sulphate (ZnSO4, 7H,O), also zincic chloride (ZnCl2), used as a disinfectant under the name of "Burnett's Disinfecting Fluid." Zincic sulphide or blende (ZnS) and zincic carbonate or calamine (ZnCO3) have already been spoken of as the natural compounds from which zinc is obtained.

CADMIUM.

Symbol, Cd. Atomic weight, 112.

This metal was discovered in the ore of zinc by Stromeyer in 1817. It has a specific gravity of 8'6, is a white metal which fuses at 442°, and crystallizes in octohedral crystals.

Cadmic oxide or oxide of cadmium (CdO) is the only known oxide of this metal. Cadmic sulphide, chloride, and iodide are well-known salts of cadmium. The last-named, iodide, has already been mentioned in connection with the photographic art.

CLASS V.

IRON, MANGANESE, COBALT, NICKEL, CHROMIUM,
URANIUM, INDIUM.

The Iron Class.

IRON.

Symbol, Fe (Ferrum). Atomic weight, 56.

SOURCES WHENCE DERIVED.

In an orbit peculiar to themselves are supposed to revolve countless fragments of a solid nature, varying in weight from tons to pounds, ounces, and grains or mere dust: these bodies are called asteroids or planetary dust; and when they enter the atmosphere of the earth, they become ignited by friction in their very rapid movement through the upper portions of the air, and, when drawn within the sphere of the attraction of the earth, they fall into or upon our planet, and are then called "meteorites.” These remarkable visitors contain a large proportion of pure metallic iron, also sulphur, phosphorus, carbon, manganese, magnesium, nickel, cobalt, tin, and copper.

Metallic iron in small quantities has been found associated with the ores of platinum. The ores of this metal are, however, legion, and amongst the most important are iron pyrites (FeS2); clay ironstone, an impure carbonate, and the source of nearly all the enormous quantities of iron made in Great Britain; the hæmatites, red and brown (the former FeO3, the latter 2Fе,О ̧, 3H,O); specular iron ore (also Fe,O,); and the magnetic iron ore or loadstone (FeO, F2O3).

The smelting of iron ore is a process which has been brought to the highest degree of perfection in this country; it is, therefore, interesting to notice first the more primitive and ancient method of reducing iron ore to the metallic state, such as that illustrated in Fig. 515, and carried on by the natives in India.

"Smelting of Iron Ore in Kasya Hills.-The following is the method pursued from time immemorial by the natives of this part of the country in working down the ores of iron so plentifully met with hereby. There are large grass huts at least 25 ft. high, the thatch of which reaches down to the ground on all sides; the interior, of an oval form, 15 by 30 ft. in the two diameters, is divided into three apartments, the central one being the smelting-room. Two large double bellows, with the nozzles pointed downwards, are set up on one side of the apartment, on the upper side of which a man stands with one foot on each, his back supported by two planks. He holds a stick in his left hand, which is suspended from the roof, and has two straps attached to it below, connected with the two bellows: these are worked quickly by a wriggling motion of the loins and the strength of the leg. The nozzles of the bellows unite in a tube which leads underground, from a sort of wind-chest, to the hearth,

about four feet in front of them. Over the hearth is a chimney of pipeclay, braced with iron hoops, 2 ft. in diameter at the bottom and about 6 ft. high; the mouth at the bottom is on the side away from the bellows, and the chimney inclined from them, to direct the heated air from the smelter towards an opening in the roof. At the right side of the bellows, and even with the top of the chimney, is a trough containing damp charcoal and ironsand. At every motion of his body the operator with a long spoon tumbles a piece of this charcoal, with the ironsand adhering to it, down the funnel of the furnace; and when a mass of melted-or rather softened-iron is formed on the hearth, it is

taken out with the tongs, and beaten with a heavy wooden mallet on a large stone by way of anvil. The iron in this state is sent down to the plains for sale or barter." ”米

Herodotus tells us that amongst the most precious gifts presented by the Indian monarch Porus to Alexander the Great was a pound of steel, the value of which at that period, according to a rough calculation of the elder Mushet, may be estimated at about £40. A pound of steel, at present prices of £14 a ton, costs, within a fraction, three-halfpence of our money. That the manufacture of steel was in later ages carried to great perfection in India, as well as in the South of Europe, especially in its application to warlike instruments, as swords, spear-heads, daggers, and the like, we have abundant evidence in specimens of ancient art.

In commerce iron is known and used in three different conditions, viz., cast iron, wrought iron, and steel. Each of these forms exhibits special physical properties, and all differ essentially in their chemical constitution.

As a contrast to the ancient method of smelting iron ore in India, we have in England the immense "blast furnace," 50 ft. high and from 14 to 17 ft. in diameter. The crude materials are roasted clay ironstone, coal, and limestone: these, with the assistance of a powerful blast of air, react on each other: the carbon deoxidizes the oxide of iron, and the limestone is the flux which melts with and carries off the earthy matter. The iron falls down and collects in what is called the crucible or hearth, and is run into rough sand moulds, and when cold is called “pig” or cast" iron.

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By the last official returns, taken from Hunt, the total quantity of iron ore raised in the United Kingdom, in 1867, amounted to 10,021,058 tons 9 cwt., the estimated value of which was £3,210,098 os. 4d. Foreign ores imported, 86,568 tons. Total quantity of iron ore converted into pig iron, 10,107,626 tons. The number of furnaces in blast were 5511.

This quantity, estimated at the mean average cost at the place of production, would have a value of £11,902,557. Into this large amount of ore Northamptonshire enters for 416,765 tons, of the estimated value of £104,191; and the North Riding of Yorkshire, or the Cleveland district, produced 2,739,033 tons, of the estimated value of £798,056. The total produce of iron ore in Scotland in the same year was 1,264,800 tons, of the estimated value of £311,200, both returns being less than the corresponding returns of the preceding year. Such are the most recent returns of a manufacture which gives direct employment to 250,000 persons, and the prosperity of which, or the reverse, affects the comforts or privations of so many thousands of our fellowcountrymen.

Pig or crude cast iron contains many foreign bodies which interfere with its use for purposes where tough, good iron is required. There are three varieties of cast iron, viz., grey, mottled, and white cast iron. They contain combined

* "Journal of the Asiatic Society," Vol. I. 1832.