Its Properties and extensive Uses—Alston Moor—Belgian Lead Mines—Galena in America—Extraction of Silver from Lead Ores—Pattinson’s Process—A great part of our wealth is due to the laboratory.

Lead was but little prized by the ancients, who, unacquainted with gunpowder, needed no bullets for war or for the chase. The history of its first discovery is lost in obscurity, but it probably became known much later than copper or tin, as less metallurgic skill is required for the smelting of the cupreous or stanniferous ores than for the reduction of galena or sulphide of lead, which is the most abundant of the plumbiferous ores, and may indeed be regarded as the only commercial ore of any value, if we except the carbonates, which are probably formed by its decomposition.

Lead, however, is mentioned both in the Book of Job and in the fourth book of Moses, ‘Oh! that my words were graven with an iron pen on tablets of lead,’ exclaims the long-suffering patriarch, and the legislator of the Jews commands his people to ‘make go through the fire, gold, silver, brass, tin, and lead, and everything that may abide it.’ The Phoenicians, who provided Greece and Egypt with Spanish lead, frequently made use of this metal to increase the weight of their anchors; and Herodotus, describing a bridge in Babylon, mentions that its stones were fastened with clasps of iron soldered with lead. The physical properties of this metal qualify it for a great variety of uses. As it is but little altered by exposure to air or water, it makes excellent pump-tubes and rain-gutters; while its considerable weight, its softness, its flexibility, and the facility with which it melts at a comparatively low temperature render it an invaluable material for the soldier’s bullet or the huntsman’s shot. Combined with oxygen it forms the pigment called red-lead, or minium, and united with carbonic acid white-lead, or ceruse, which is still more frequently used in painting.

In the manufacture of glass and crystal it plays an important part, as it forms one of the chief ingredients of flint-glass and crown-glass, of which, as is well known, the achromatic lenses are made which have so wonderfully improved the distinctness of our telescopes. United with tin it forms an alloy which is more fusible than either metal alone, and which is consequently used as a solder by the plumbers, while with antimony it combines into a hard mass which serves to make letters for the printing-press. All these various uses absorb immense quantities of lead, and render it one of the most valuable products of the subterranean world.

Among the lead mines of Europe we find the first rank occupied by those of Spain, which in 1863 furnished the enormous mass of 309,940 tons of galena. The principal mines are situated in Guipuzcoa, Catalonia, Arragon, the Sierra Morena, and, above all, in the mountain chain of the Alpujarras, where the rocks of the Sierra Gador are everywhere traversed by veins of galena. The production of North Germany is also very considerable. In 1865 Prussia furnished 57,808 tons of galena, and the Hanoverian Hartz Mountains, which produced 101,411 tons in 1864, and now belong to the same monarchy, have raised its previous production to a threefold amount.

The chief lead mines of England are situated near Alston Moor, where the three counties of Northumberland, Durham, and Cumberland meet together. The lofty hills of the district, bare of wood and almost wholly covered with marshy heaths, are intersected by the valleys through which run the Tyne, the Wear, and the Tees, with their numerous branches. The country, though little frequented by tourists, is wild and picturesque; but the deep gorges with which it is furrowed have more than a mere romantic interest, for they lay open to view numerous veins of ore, and direct the operations of the miner to the places where it is sufficiently abundant to reward his toil. The town of Alston, the mining centre of the district, is beautifully situated close to the river Tyne, which, about five miles above it, ascends, between lofty hills, to the foot of Cross Fell, this picturesque mountain giving a character of considerable grandeur to the surrounding scenery. The mines of the Alston Moor district produce annually about 25,000 tons of lead. The waters are drawn off by long adit levels, and the ores are dragged out by horses to the day. This region extends southward to the Yorkshire valleys of Swaledale, Arkendale, and to Grassington, where numerous lead mines are worked under very similar circumstances. The Yorkshire mines yielded in 1856 8,986 tons of lead.

Another important lead district lies in the northern part of Derbyshire, in the hilly country of the neighbourhood of the Peak, so well known and so often visited for its picturesque beauty. The mines of Derbyshire, which yield annually 5,000 tons of lead, are getting exhausted; they are very numerous, but in general inconsiderable.

Next to Alston Moor the lead mines of Flintshire and Denbighshire are the most productive, furnishing annually nearly 6,000 tons of lead. An important group of veins of lead occurs in the slaty rocks of Cardiganshire and Montgomeryshire, all of which have an E.W. direction; although so far from parallel that they often meet, and frequently form at such points of intersection ‘courses’ of ore. Some of these mines were very profitably worked in the seventeenth century, and during the last thirty years several of them have been highly productive.

There are considerable lead mines in the south of Scotland, at Wanlockhead and Leadhills in Lanarkshire; and those of Strontian, in Argyleshire, likewise deserve to be noticed. The Isle of Man has two important lead mines, the Foxdale and Laxey, the former remarkable for the great size of its main lode. The elevated tracts of Wicklow likewise contain some valuable lead mines, at Luganure and Glenmalure. In 1866 the total produce of our lead mines amounted to 91,047 tons of galena, which yielded 67,390 tons of metal.

The island of Sardinia, already renowned among the ancients for its rich lead mines, produces about 15,000 tons, or nearly as much as France, where however the extraction of galena has of late years made considerable progress.

Belgium, which in 1841 produced no more than 34 tons, raised in 1864 no less than 16,780 tons, chiefly from the mines of Bleyberg-À-Montzen, situated in the carboniferous limestone near Verviers. To render these rich deposits available, vast difficulties had to be surmounted by the united powers of enterprise, capital, and engineering skill. Rivers and brooks, diverted from their ancient course, were made to flow through new water-tight channels, and such is the amount of drainage required in that aquiferous region that engines of two thousand horse-power have to raise from a depth of 360 feet a daily quantity of 800,000 cubic feet of water.

In Greece the immense mounds of scoriÆ accumulated near the ancient silver mines of Laurium, have been found to contain about ten per cent. of lead. Their total mass is estimated at no less than 3,000,000 tons, and they afford a convincing proof both of the importance of the ancient silver production of Attica, and of the imperfection of the old Athenian mining operations. A French company has lately been formed for smelting this prodigious accumulation of scoriÆ, once cast aside as rubbish.

In Siberia the famous lead mines of Nertschinsk, where many an unfortunate exile is doomed to end his days, are worked merely for the silver contained in them.

In South America, the Chilian lead mine of Mina Grande, near Coquimbo, is renowned for its extreme richness, and Brazil has considerable veins of galena, in the province of Minas Geraes; but probably the United States of North America (Wisconsin, Arkansas, Iowa, Illinois), possess the largest galena deposits in the world. In Wisconsin, they extend all over a vast territory of more than 4,000 square miles. As yet the works are conducted in the most negligent manner, by a crowd of adventurers. In winter, when the air in the pits is more salubrious, and agricultural labour ceases, needy farmers, bankrupt traders, and thriftless artisans flock from all parts to the lead country for the purpose of repairing their broken fortunes. In summer when malaria renders the pits extremely unhealthy, this nomadic population melts away like chaff before the wind. Yet, in spite of the rough mode of extraction which prevails in the American lead country, the mines of Iowa, Wisconsin, and Illinois yielded about 20,000 tons of lead in 1866, and their produce is constantly increasing.

In all lead mines, the galena often occurs in pieces so large that they do not require to be separated from the veinstone by the processes of stamping and washing. They are then called pure ores, and the most simple preparation is sufficient to prepare them for the smelting furnace. When the ore has been picked and so far prepared, it is first roasted or heated in a reverberatory furnace, an operation which causes the oxygen of the air to combine with the two elementary bodies of which galena is composed. After undergoing this chemical change, the ore is now mixed with coke, charcoal, or peat, and reduced by smelting in a small blast furnace of a peculiar kind. Under the influence of heat, the carbon of the coal, uniting with the oxygen of the ore, flies off in the form of carbonic acid gas, while the metallic lead, which in the finer ores amounts to 70 or 80 per cent., sinks to the bottom of the furnace. Almost all the varieties of galena contain a greater or less proportion of silver, which it is often found worth while to separate from them. This process is at present effected according to a most ingenious method, founded on the circumstance first noticed in the year 1829, by the late H. L. Pattinson, of Newcastle-on-Tyne, that when lead containing silver is melted in a suitable vessel, afterwards slowly allowed to cool, and at the same time kept constantly stirred at a certain temperature near the melting point of lead, crystals begin to form. These, as rapidly as they are produced, sink to the bottom, and on being removed are found to contain much less silver than the lead originally melted. The still fluid portion, from which the crystals have been removed, will at the same time be proportionally enriched. By repeated meltings and crystallisations in a series of cast-iron pots with fire-places beneath, the workman is thus able to deprive almost entirely of its silver by far the largest portion of the lead operated upon, while the remainder becomes an exceedingly rich alloy of both metals, so as to contain fifty times its original proportion of silver. This rich lead is subsequently exposed in a refining furnace to a strong blast of air at a high temperature, fresh supplies of lead being constantly introduced as the operation proceeds. By this means the lead becomes rapidly oxidized and converted into litharge, which partly runs off in the fluid state, and is partly (about 10 per cent.) lost by sublimation, while the silver forms a cake at the bottom of the cupel. The brightening of the silver, which lustrously shines forth at the moment of the separation of the last traces of lead, indicates the precise period at which the operation should be ended, and the blast is then turned off and the fire removed from the grate. Before the introduction of Pattinson’s ingenious process, the separation of the silver from the lead was attended with a much greater loss of the latter metal, as greater quantities had to be cupelled to effect the same result. The economy obtained amounts to no less than 98 per cent.; for where formerly 100 cwt. of lead were lost by sublimation, the same quantity of silver is now obtained with a loss of no more than 2 cwt., and at the same time with a considerable saving of fuel.

Ores very poor in silver, as for instance those of Alston Moor or Derbyshire, which formerly could not be profitably cupelled, are now advantageously treated by the Pattinson process. This is but one example of the valuable practical results which may be obtained from a single scientific discovery. But chemistry has introduced thousands of similar technical improvements in almost all branches of manufacturing industry, and were we to add together the profits thus obtained, we should find that a great part of our wealth is due to the laboratory.