XVIII.

THE METALS AND METALLIC ORES.

THERE is no chapter in Geology more interesting than that which deals with the Metals and Metallic Ores. These substances lie at the foundation of all the higher arts and industries, and little progress can be made, even in civilisation, without some acquaintance with their nature and uses. Man restricted to tools and implements of wood, bone, or stone, can never successfully combat with the forces of nature, or modify them to his service and comfort. He is essentially a savage. But the moment he can arm himself with a weapon of metal, or handle a metallic tool, he gains an ascendancy over external nature, and his course, mentally as well as physically, is thereafter onwards and upwards. He always passes through the successive stages of stone, bronze, and iron; and not till he has arrived at the last can he be said to possess tools, implements, and machinery sufficient for the arts and industries of civilised existence.

To the metals man owes his finest and most efficient tools, implements, and machinery; his most beautiful and durable ornaments; his most brilliant dyes and pigments; his most convenient medium of exchange; and, indeed, very much of that power which, as an intelligent being, he exercises over the domain of nature. They run through all his arts and industries his endless machinery, instruments, and apparatushis steam-engines, railways, ships, and telegraphs. In fine, there are few or none of his economic processes in which they do not directly or indirectly bear a part. As they are found in nature, it is usual to speak of them as Native Metals and Metallic Ores-that is, as metals occurring in a pure and simple state, or as metals chemically combined with other substances -thus forming oxides, sulphides, carbonates, silicates, and the like. In the present chapter we shall direct attention principally to their geological recurrence, their abundance, and the

facilities with which they can be procured, leaving the processes by which they are reduced, smelted, alloyed, and manipulated, to the metallurgist and technologist.

1.-NATIVE METALS.

Comparatively few of the metals occur in a free or uncombined state that is, as pure and simple elementary substances. Those most frequently found are—gold, platinum, palladium, silver, mercury, copper, arsenic, antimony, bismuth; and those less frequently and doubtfully-iron, lead, zinc, and tin. There also occur, though less abundantly, a series of double-metals, or amalgams of gold and mercury, of silver and mercury, of gold, silver, and mercury, of platinum and iridium, of iridium and osmium, and the like; but these we need not especially refer to.

Gold.

Gold, so well and widely known, occurs in various shades of gold yellow, has a hardness from 2.5 to 3.0, and a specific gravity from 16.0 to 19.5, according to its purity. It has extreme permanence in air and fire, being little tarnished by any amount of exposure, and melts at 2016° Fahr. It is also extremely malleable and ductile, its malleability being such that it may be beaten into leaves not more than of an inch in thickness, and its ductility so great that one grain is capable of being drawn out into 500 feet of wire. It readily forms alloys with other metals; and in coinage, as well as in the arts, is generally so alloyed (with copper, silver, &c.) to improve its hardness, and so render it better able to resist the tear and wear of circulation, handling, and cleaning. If 24 carats be taken as the standard of purity, any stated number below 24 will indicate the amount of admixture. Gold is not acted upon by the common acids, but yields to chlorine and nitro-muriatic acid, forming a chloride of gold which is soluble in water.

Geologically, gold is a widely distributed metal, and occurs, with few exceptions, in quartz-veins which traverse the metamorphic or older schistose and slaty rocks. It appears in minute disseminated particles, in scales, strings, arborescent plates, and in nuggets from a few grains to many pounds in weight. When not found in situ in the veinstone, it is usually distributed in stream-drifts of sand and gravel which have been wasted and worn, and transported in course of ages from the mountain-veins to the valleys below. It was from such drifts

that the ancients gathered their gold in dust, and scales, and pellets; and it is still from such deposits in the Urals, California, Australia, New Zealand, and other regions, that the great commercial supply of the metal is obtained. It is not till the drifts get exhausted, or in districts where stream-working is not remunerative, that the auriferous veins are attacked; though, generally speaking, where the vein is a fair one, it forms the steadiest and most reliable source of supply. What are termed "gold ores are not ores in the strict sense of the term; for whether native amalgams or ores of other metals, the gold they contain, as may be seen by referring to the next section, is still in the free and uncombined metallic condition. According to the present state of our knowledge, the metal is always native, whether occurring in veins of quartz, calc-spar, and baryta, disseminated through the older schistose rocks, incorporated with other ores, or scattered abroad in drifts of sand and gravel.*

While gold occurs notably in the drifts of the Urals, Brazils, California, Nevada, Colorado, British Columbia, Australia, and New Zealand, it is also found in minor quantities along the river-courses of many other regions-India, Africa, the United States, and Southern Europe-and very sparingly in our own islands, as in Wicklow, Devon, Wales, and the Scottish Highlands. It is mined in Brazil, Central America, Mexico, California, Australia, Spain, Hungary, Transylvania, the Urals, Altai Mountains, and in Sweden; but attempts at mining in Britain (Devon and Wales) have hitherto proved unremunerative. The metallurgical processes for the reduction and refining of gold lie beyond our province; but whether by washing and smelting, by amalgamation with mercury, by treatment with alkalies or other modes of liquation, some of them require considerable chemical skill and nicety of manipulation.

The statistics of gold are very imperfect, and in most cases

* With regard to the occurrence of gold, the following remarks by P. B. Smyth, Secretary of Mines for the Colony of Victoria, may be of use to the geological student: "Gold is now found to occur not only in quartz-veins and the alluvial deposits derived from these and the surrounding rocks, but also in the claystone itself; and, contrary to expectation, flat bands of auriferous quartz have been discovered in dykes of diorite, which intersect the upper Silurian or lower Devonian rocks. Quartz of extraordinary richness has been obtained from these bands, and the new experience of the miner is leading him to look for gold in places hitherto entirely neglected. It is probable that some time may be lost, and that his labours may not always be well directed or successful, but it is commendable that he should not be deterred from explorations by warnings and remonstrances founded on surmises often baseless. If he had already followed the older precepts, we should at this moment have been dependent for our yield of gold on the shallower alluviums, and the surface only of the veins of quartz."

little better than guesswork. Not only does the quantity raised in any given locality vary from year to year, but new localities are unreported, and the success of mining adventures is often either kept secret, or exaggerated for speculative purposes. Roughly estimated, the total yield of the world may be set down at 460,000 lb. troy, representing an approximate value of £23,000,000.

The uses and applications of gold in the arts and industries are innumerable. It is employed for coinage, for domestic and personal ornaments, for the formation of alloys, for the preparation of pigments, and for gilding of other metals, wood, plaster, and paper-hangings, and for the preparation of wire and leaf in all their multifarious applications. The extension of its use is generally the test of a nation's wealth, and year after year it is more and more employed in the fabrication of articles of luxury and ornament.

Platinum.

The metal Platinum or Platina, discovered in 1741 in the mines of Peru, and so named by the Spaniards in allusion to its silvery colour-platina, the diminutive form of plata, silver -is found only in a native or metallic state. What is termed "platinum ore," or crude platinum, is merely an admixture with other metals, such as palladium, rhodium, osmium, iridium, titanium, gold, silver, iron, and copper. Since its discovery in Peru it has been found in Brazil, California, the Urals, Borneo, and other countries. It is usually obtained from drifts in rounded grains or flattened pellets, of a metallic lustre and white colour. When pure it has very much the colour of silver, but of inferior lustre. It is the heaviest of known metals, its specific gravity after hammering being about 21.5. It is exceedingly ductile, malleable, tenacious, and difficult of fusion, but capable of being welded at a high temperature. It undergoes no change under the combined action of air and moisture, resists the strongest heat of a smith's forge, but can be melted by voltaic electricity, or by the oxyhydrogen blowpipe. It is not acted upon by any of the pure acids, but is dissolved by chlorine and nitro-muriatic acid, and is oxidised at a high temperature by pure potassa and lithia.

A metal possessed of such properties is eminently fitted for chemical works and laboratories; hence it is manufactured into crucibles, evaporating dishes, stills for concentrating sulphuric acid, spoons, blowpipe-points, tongs, forceps, wire, and similar articles. It is also used for galvanic apparatus, ornamental work in chains and trinkets, medals, and at one time by the Russian Government for coin. It forms alloys with

iridium, with iridium and rhodium, and with gold, which are said to possess properties of resistance superior to the pure metal; and with equal parts of steel it constitutes the best white speculum-alloy known. According to Wagner, the amount of metallic platinum annually produced does not exceed three tons, and of this the greater portion comes from the Urals.

Palladium.

The metal Palladium (Pallas, the goddess), discovered by Wollaston in 1803, is usually found in very small grains, of a steel-grey colour and fibrous structure, in auriferous and platiniferous sands. Its specific gravity is about 11.5; and in fusibility it stands intermediate between gold and platinum. When native it is alloyed with a little platinum and iridium, or with gold and silver, as in the Porpezite of Peru, which consists, according to Berzelius, of 85.98 gold, 9.85 palladium, and 4.17 silver. It is ductile as well as malleable, and is considerably harder than platinum. It is oxidised and dissolved by nitric acid; but its proper solvent is nitro-hydrochloric acid. It forms alloys, most of which are brittle, with arsenic, iron, bismuth, lead, tin, copper, silver, gold, and platinum; the alloy with nickel is ductile. It is sometimes used for the finely divided scales of mathematical and astronomical instruments; for the smaller chemical weights; and 1 per cent added to steel produces a smoother cutting edge.

Silver.

The early and well-known metal Silver is found native in the older rocks, in threads and strings, in arborescent moss-like aggregates, and in plates and nuggets often of considerable magnitude. In its native state it often occurs as an alloy with gold, platina, mercury, copper, or arsenic-more frequently, perhaps, with mercury than with any other metal. Two specimens of "native silver" from Allemont, in Dauphiné, yielded respectively to Mr Church's analysis 26.15 and 18.34 of mercury. Being principally obtained from its ores, or from other ores with which it is in intimate union, its nature, properties, and uses will be better considered under the section, "Metallic Ores."

Mercury, Copper, Iron, &c.

The same may be said of Mercury, Copper, Arsenic, Antimony, and Bismuth, which, though occasionally found native, or as native alloys, yet occur in quantities too unimportant to affect their commercial values. The remark is still more applicable to Iron, Lead, Zinc, and Tin, which are all less or more doubt