Manganese is likewise a metal which has not yet left the domain of the laboratory, but some of its ores are of considerable and increasing importance. The grey and black oxides of manganese are largely used for the manufacture of the chloride of lime, a substance well known for its bleaching properties. They also serve in the fabrication of flint-glass, as a means for correcting the green tinge which it is apt to derive from iron, and are employed in the manufacture of various kinds of steel. The ores of manganese are chiefly provided by the mines of Nassau, which in 1864 yielded 14,460 tons, and of Huelva in Spain, which furnished 24,430 tons in 1865. Our Cornish mines likewise produce considerable quantities, but are still far from being able to supply the wants of our colossal industry, which, in 1866, required the importation of no less than 48,700 tons of oxide of manganese from foreign countries.
Cadmium, which accompanies most of the zinc ores, was discovered by Stromeyer in 1818. Its sulphuret affords a fine yellow pigment; but the metal itself, which has the colour and lustre of tin, and is very fusible and ductile, has no commercial value.
Rutile, a red-brown mineral, occurring in small quantities in the Alps, Norway, and many other localities, where it is generally found in crystals, imbedded in quartz, was found by Klaproth, in 1795, to be the oxide of a peculiar metal which, according to the old fashion of giving mythological names to new planets and metals, obtained the name of Titanium. The metal, which has a copper-red colour, has not hitherto been applied to use; but rutile is employed as a yellow colour in painting porcelain, and also for giving the requisite tint to artificial teeth.
Like Titanium, the metal Molybdenum, discovered by Hjelm in 1782, is as yet interesting only in a scientific point of view; but one of its salts is used by the cotton-printers as a valuable colouring matter, and another is indispensable as a re-agent in many chemical researches. Thus more than one of the modern metals has already become an important object to the porcelain-painter or the dyer.
Aluminium, the metal which Sir H. Davy discovered in clay or alumina, and of which the purest native oxides are the varieties of corundum (oriental ruby, sapphire, &c.), has of late become of technical importance, and though the cost of its production is very great, as a pound of aluminium is worth about 4l., yet it already serves for many purposes. Its silvery lustre and perfect unalterability by atmospherical influences render it an excellent material for objects of art and ornament, and from its low specific gravity (256⁄100) it makes excellent tubes for telescopes and opera-glasses, which when composed of any other metal are of a fatiguing weight. Even culinary vases have already been made of aluminium, for, besides its perfect innocuousness, it cools very slowly when heated, and greasy substances do not adhere to it. Its high price is the only obstacle which has hitherto limited its uses. With copper it forms an alloy (aluminium-bronze) discovered by Dr. John Percy, which possesses the hardness, tenacity, and malleability of iron without its liability to rust, and consequently has already found numerous applications. The beautiful gold colour of this alloy makes it a valuable material for the fabrication of the vases and ornaments used in Catholic churches, and a recent decree of the Pope has authorised its employment for this purpose.
Magnesium, the metallic basis of magnesia, a native earth widely disseminated in the mineral kingdom, and forming a constituent part of whole mountain chains, had ever since its discovery by Sir Humphry Davy been a mere object of curiosity, when a few years ago, Mr. Sonstadt, an English chemist, succeeded in producing it in larger quantities. Its silvery brilliancy, hardness, and ductility, its low specific gravity, and unalterability by air and water, are qualities which will probably lead to an extensive employment when a cheaper method of production shall have been discovered; but even now it has found a highly interesting use. It is so easily inflammable that a wire of considerable thickness can be ignited in the flame of a candle, and the light evolved by the combustion is of almost solar intensity. In lighthouses it serves to guide the mariner in his course; it lights up the obscurest recesses of stalactital caverns, and with its assistance the photographer no longer depends upon the sun, and reveals to us the hidden paintings and sculptures of rock-tombs and temples as distinctly as if they were exposed to the light of day.
Sodium, the metallic basis of soda, was discovered by Sir Humphry Davy in 1807. It is lighter than water, and white and lustrous as silver; but exposure to air almost immediately converts it into soda. Thus it can never become directly useful, like aluminium or magnesium; but being indispensable for reducing the ores of these two metals, it renders important indirect services, and is consequently produced in considerable quantities.
Palladium, one of the hardest and heaviest of metals, is of a steel grey colour, passing into silver white. Its alloy with silver, which has the valuable property of not tarnishing in air, is eminently fitted for the manufacture of delicate scientific instruments. The Wollaston medal, given by the Geological Society, is, in honour of its discoverer, made of palladium, which is considerably dearer than gold.
In 1804, the same eminent philosopher discovered another metal in native platina, to which he gave the name of Rhodium. Mixed with steel in the proportion of one to fifty, rhodium produces an excellent metal for making the sharpest cutting instruments, and a mixture of equal parts of rhodium and steel makes the best telescopic mirrors, as it is not liable to be tarnished. It is also employed for making the unalterable nibs of the so-called rhodium pens.
Thallium, though one of the newest metals, as it was discovered by Mr. Crookes as recently as 1861, already bids fair to render some important services. It imparts to optical glasses a considerable density and dispersive power, and should no other use be found for it, this alone would render it a valuable acquisition.