piece of metal and a drop or two of water be allowed to fall upon it), but effervesces violently, and swimming upon its surface, gradually diminishes with great agitation, decomposes the water, evolving hydrogen gas, and forming an alkaline solution of soda. With hot water it takes fire at once, and burns with a bright yellow flame. Like potassium, it is best preserved under naphtha.

Sodium may be united with chlorine, but only in one proportion; this is the important substance common salt, chemically termed chloride of sodium. It consists of 36 chlorine+24 sodium, and may be directly obtained by combustion, or by decomposing any compound of chlorine, by sodium.

Potassium and this metal may be combined in several proportions; 8 potassium + 1 sodium will swim in naphtha, and like the alloy of 3 potassium + 1 sodium is fluid at the common temperatures of the atmosphere.

This metal occurs in nature in abundance, but always in a state of combination. The chloride is the most important native ore, which, as rock-salt, is found in immense beds in the solid crust of the earth; it occurs, also, in a state of solution in the sea, and probably in every natural water. Compounds of this metal are found in several minerals and in most soils; they occur, although in small quantities, in most land plants, but abundantly, as kelp illustrates, in those of the sea. It is also found in a state of the chloride in the higher animals who instinctively swallow large quantities of common salt.

CHAPTER XLVI.

STRONTIUM.

IN 1807, Sir Humphrey Davy ascertained that strontia (which was discovered in 1787, in a mineral taken to Edinburgh, by a fossil dealer, from a lead mine at Strontian, in Argyleshire, whence its name is derived) consisted of 100 parts of a metal, which he named Strontium, and 18.181 parts of oxygen. He made into a paste with water native

carbonate of strontia, and placed it on a small platinum tray; he then placed a globule of mercury within a cavity made in the surface of the paste. He then connected the platinum with the positive pole, and the mercury with the negative pole of a pile of about 100 double plates. An amalgam of mercury and strontium was thus obtained, which he introduced into a tube of glass made without lead, which was then filled with the vapour of naphtha, bent into the form of a retort, hermetically sealed. He then separated the strontium from the amalgam, by driving off the mercury by heat.

Strontium resembles barium in most of its properties. It is a malleable metal of a pale yellow colour, having a specific gravity of 2:54. It decomposes water rapidly, with the evolution of hydrogen gas; the water is converted into a solution of strontia. When heated in the open air, it burns with a yellowish flame, with the emission of sparks. Its compounds are not poisonous.

This metal may be united with oxygen in two proportions. The protoxide of strontium, called strontia, and strontian, is best obtained by decomposing the nitrate by the aid of heat; it is a grey, poisonous, alkaline earth resembling baryta (but is not poisonous), and has a violent affinity for water; by affusion of this liquid, heat is evolved, and so much earth is dissolved that crystals separate on cooling. One hundred parts of strontium unite with 18·181 of oxygen, to form the protoxide; and with 36-362 to form the peroxide, called by some, the deutoxide or binoxide.

Strontium is found in the lead mines of Strontian, in Argyleshire, where it occurs as a carbonate, sulphate, &c. It occurs in the rare pale-green mineral strontianite, which consists of strontia combined with carbonic acid and water; and which is found in Salzburgh, and at Strontian. It is met with also in baryto-strontianite, a pale blue mineral containing some barytes and lime, as well as Strontia and carbonic acid, and occurring only at Stromness, in Orkney. It is found also in celestine, which contains equal parts of Strontia and sulphuric acid, near Bristol, in the sulphur mines of Sicily, and in the United States.

This metal forms the chief ingredient in producing that beautiful red-fire, which recently has been introduced in theatrical representations.

CHAPTER XLVII.

TELLURIUM.

TELLURIUM, which derives its name from the Latin tellus, the earth, was discovered in 1782 by Müller, of Reichenstein, in the aurum paradoxicum or problematicum, which has the appearance of an ore of gold, but only very little can be extracted from it. In 1798, Klaproth established its existence not only in this, but also in some other ores of gold found near Zalethna, in Transylvania; he also examined its properties more minutely and gave to the metal the name which it now bears.

It is a white metal, somewhat similar in its appearance to antimony, and possesses great metallic lustre, and a lamellar fracture: it is so brittle that it may easily be pulverized; it is not so good a conductor of electricity as antimony or bismuth. It fuses at a temperature of 620 degs. Fahrenheit; if the heat be increased, it boils, and may be distilled; and when exposed to the action of the blow-pipe on charcoal in atmospheric air, it burns with a pale blue flame, bordered with green, and forms a white vapour which possesses a pungent smell, and which condenses into a white oxide. This oxide heated on charcoal is reduced with a kind of explosion, and soon again volatilized. It appears to contain about 16 per cent. of oxygen.

Tellurium has a specific gravity of 6·115, and is soluble in the nitric and nitro-muriatic acids, but its solutions are decomposed by the addition of water. It forms with oxygen two compounds :-tellurous acid and telluric acid.

It is a very rare metal found chiefly in the mines of Hungary and Transylvania, occurring sometimes in a native state, but usually in combination with sulphur, arsenic, iron, lead, silver, and gold. Native tellurium, which has a tinwhite or steel-grey colour, and a metallic lustre, and which is found crystallized, and massive in the mines of Transylvania, consists of 92.55 Tellurium + 7·20 iron + 0.25 gold.

CHAPTER XLVIII.

TERBIUM.

IN 1840, Mosander discovered this peculiar metal in the state of oxide in the minerals gadolinite, orthite, &c., combined with yttria, and the oxide of erbium; but the oxide has not yet been reduced to the metallic state.

The oxide of terbium has hitherto been procured only in small quantities, and its properties are but little known. It may be distinguished from that of erbium in not being changed to a dark orange-yellow colour when heated in contact with the atmosphere. It is insoluble in water, and in the caustic alkalies.

CHAPTER XLIX.

THALLIUM.

THIS metal has recently been discovered by Crooke, an English chemist and distinguished philosopher, in a residue of impure sulphur. Comparatively little is at present known of this metal, but, we think that this, as well as several others of the new metals, bids fair to become a very useful substance.

THIS metallic substance was discovered in 1827, by a Swedish chemist, named Berzelius, in a rare earth (which he had found in a mineral occurring near Brevig, in Nor

way, termed thorite), to which he had given the name of thorina, in honour of the fabulous deity Thor.

If thorina be converted into chloride of thorinum, and heated with potassium, and the mass washed, a deep leadengrey coloured powder will be obtained, which, when pressed in an agate mortar, will acquire an iron-grey tint and a metallic lustre.

Thorinum is not acted upon by water, either hot or cold. When heated in common air it burns brilliantly, and the oxide of thorinum, or thorina, is formed, which has a snowwhite colour, and is devoid of any trace of fusion; it may also be procured by decomposing the chloride by means of an alkali; when strongly heated its density is 9-402, and it is then insoluble in any acid except the sulphuric, and in that with difficulty.

Thorinum is scarcely at all acted upon by nitric acid, and slowly by the sulphuric; but hydrochloric acid quickly dissolves it, with the evolution of hydrogen gas.

TIN must have been known very early, as it is mentioned in the writings of Moses (Numb. XXXI., 22) as being one of the metals that may "abide the fire" for purification. An alloy of tin and copper was much employed by the ancients for their coins and edge-tools, iron then being comparatively scarce, and very expensive. In Ezekiel xxvii., 12, we read that the Tyrians imported it from Tarshish; and a levelling instrument of tin is mentioned in Zech. iv., 10. This word was also used for a refuse of lead and silver, Isaiah i., 25.

It occurs in South America, in the East Indies, in Germany, and in Saxony; but in England it is chiefly obtained from Cornwall and Devonshire. The Cornish mines have been noted from a very remote period, and seem to have attracted various foreign merchants, and,

H