This may be remedied by remelting the copper with a little charcoal, and stirring with a pole of green wood. Commercial or tough-pitch copper is never pure, but the impurities are neutralised by the presence of a little oxygen. If the poling referred to above be continued too far, the neutralising oxygen is removed and the other impurities present act on the copper prejudicially, making it brittle. The copper is then said to be over-poled.

Copper unites directly with sulphur when the two bodies are heated together forming cuprous sulphide, which is of a dark bluish-gray colour, shows a finely-granular fractured surface when broken, and has a metallic lustre.

Phosphorus is highly injurious to copper when allowed to remain in it, but a small quantity may, under certain circumstances, exert a refining influence, provided the whole of it is afterwards removed.

The element silicon, when reduced from sand by the action of carbon, unites with copper, making it much harder, and causing it somewhat to resemble gun-metal in colour, but diminishes its toughness and malleability.

Lead, arsenic, and antimony have a very injurious action on copper, making it hard, brittle, and cold-short.

The common impurities in copper are iron, arsenic, antimony, and cuprous oxide; sometimes tin, bismuth, sulphur, lead, nickel, and cobalt are present. The varieties of commercial copper are :-rosette or Japan copper, the surface of which presents a peculiar red colour, due to a coating of oxide, formed by throwing water on the surface of the metal while in a heated state. Bean-shot and feathered-shot copper, which are obtained in the form of globules and flakes respectively, by running the metal into hot or cold water. Tough-cake is a variety cast into rectangular slabs, convenient for rolling, etc. Best-selected is the name applied to the purest variety of commercial copper, special care being taken to free it from sulphur, arsenic, antimony, and iron. Russian-copper, which generally contains traces of iron, but is otherwise very pure. Chili-bars. This variety, as imported

into this country, is prepared in bars weighing about 200 lbs. each; the copper being in a raw state, requires to be refined before it is ready for use.

Mercury. This is the only one of the useful metals which is liquid at ordinary temperatures; it is also called quicksilver, and has been known from the most remote times. It has a silver-white colour with a brilliant lustre; is devoid of taste or odour when pure; at a temperature of 360° it boils, and at 39.4° C. it solidifies, forming a soft, white, malleable mass, exhibiting a granular structure on the freshly fractured surface. It has a high and fairly regular coefficient of expansion for heat, which renders it suitable for thermometers and similar instruments; its specific heat is '0332, and its density at 4° C. is 13.59. Liquid mercury does not oxidise in air, except when near its boiling point, which forms a ready means of detecting the presence of base metals, such as lead and antimony, added as adulterations, or present as impurities. Impure mercury, when exposed to air or oxygen, becomes coated with a gray film, due to the oxidation of the impurities. At its boiling point mercury is slowly oxidised to mercuric oxide HgO. It combines directly with sulphur, forming an important compound, mercuric sulphide or vermilion HgS.

Mercury unites with most metals forming "amalgams," some of which are liquid, others semi-liquid, and some solid. The solid amalgams are regarded as chemical compounds, while the liquid amalgams may be solutions. of compounds in excess of mercury, but the affinity is feeble, as the mercury is partially expelled by pressure, and completely so, in most cases, by heat. Amalgams are formed (1) by rubbing the metal in a finely divided state with mercury, an increase of temperature facilitating the amalgamation; (2) by dipping a metal into the solution of a mercury salt; (3) by voltaic action, as when a metal is placed in contact with mercury and an acid; (4) by mixing a metal, such as gold, with an amalgam of a highly positive metal, such as sodium.

Mercury sometimes occurs in the metallic state, sometimes as an amalgam with silver, and occasionally as chloride, bromide, and iodide of mercury. The chief source of the metal is the sulphide HgS, known as cinnabar.

Lead. This metal has a bluish-gray colour, and possesses considerable lustre; it is malleable, ductile, and tough, but has a feeble tenacity. The lustre of a freshly cut surface soon becomes dim when exposed to the air, owing to the formation of a film of suboxide of lead. Pure lead emits a dull sound when struck, but the presence of impurities renders it more sonorous; also when the pure metal is cast in the form of a hollow sphere it becomes somewhat sonorous. Its specific gravity is 11-45, and all base metals, when alloyed with it, lower its density. Its melting point is about 330° C., and it is not well adapted for castings, since it contracts considerably on solidifying. It is so soft that it can easily be cut with a knife, and squirted into the form of tubes or rods; two clean surfaces of lead can easily be welded together by pressure in the cold, and also when in a finely divided state, the metal can be pressed into a compact mass. Its specific heat between 0° and 100° C. is 0314, and its coefficient of expansion is 00003 for each degree between 0° and 100° C.

If lead is boiled with water containing oxygen it is partially dissolved, and the liquid affords an alkaline reaction. The metal is oxidised when exposed to moist air; it is somewhat volatile when heated in air, forming lead oxide PbO, and this oxide acts as an oxidising agent on many metals, such as copper, zinc, iron, etc. Lead and sulphur unite when heated together, forming lead sulphide PbS, which is a bluish-gray, brittle, and crystalline body.

Commercial lead is often nearly pure, but it generally contains some silver, copper, antimony, tin, and sulphur; and occasionally iron, arsenic, zinc, and manganese.

Bismuth is a hard, grayish-white metal with a reddish tint and bright metallic lustre. Its specific gravity is 9.9, which may be reduced by pressure; it melts at 270° C. and

3

volatilises at a high temperature, burning with a blue flame, forming flowers of bismuth BigO,; it expands in the act of solidifying. When the metal is melted, and allowed to cool until its surface begins to solidify, the crust broken, and the metal poured out, fine large crystals are obtained. • They oxidise in air, and frequently become covered with an iridescent film of oxide. Bismuth unites with sulphur, forming a dark-gray, metallic-looking sulphide Bi2S3.

Bismuth serves for the preparation of many pharmaceutical products and cosmetics. The chief use of the metal is in the preparation of fusible alloys, the melting points of which can be altered according to the proportions of their constituents. It occurs in nature in the metallic state, as bismuth-glance BiS, as bismuth- ochre Bi20, and often in company with silver, lead, tin, copper, and cobalt

ores.

TIN GROUP. TIN, ANTIMONY, AND ARSENIC

§ 8. Tin is a white metal with a brilliant lustre; very malleable, as seen by the thinness to which tin-foil can be reduced. A bar of tin when bent produces a crackling sound, known as the "cry of tin," supposed to be due to the grinding action of its crystals over each other. Its specific gravity is 7.3, it melts at 230° C., and may be somewhat strongly heated without volatilising. When raised to a temperature near its melting point, and allowed to fall from a considerable height, the metal breaks up into the form of long grains, known as grain-tin. When tin is melted, and poured into a mould at a temperature little removed from the point at which it solidifies, the surface remains bright, if pure, but the presence of a little lead, iron, or other base metals imparts a more or less dull and frosted appearance, so that the brilliancy of the surface is a test of purity. Tin is easily crystallised superficially by treating its surface with a mixture of dilute sulphuric and nitric acids; the ornamental appearance, known as Moirée Metallique, is obtained in this way. Tin is an

inferior conductor of heat and electricity; it takes a high polish, and the radiation of heat from its surface is small. It forms a valuable metal for coating culinary vessels. It is little affected by air at ordinary temperatures, and is therefore used for coating iron to protect it from rust. It unites readily with sulphur on the application of heat, forming stannous sulphide SnS. Commercial tin often contains small portions of lead, iron, copper, arsenic, antimony, bismuth, tungsten, and sometimes manganese and zinc. The tin of commerce is quoted as common, refined, and grain-tin. The refined-tin is made from the best ores, and is more perfectly refined than common tin. Grain-tin is obtained from the best pigs, which are heated and dropped from a height, as referred to on previous page.

The only important ore of tin is tin-stone, which contains tin dioxide SnO2.

Antimony. Ordinary commercial antimony is often very impure, containing iron, lead, arsenic, and sulphur, and is called "regulus of antimony." Antimony is a brilliant bluishwhite metal, highly crystalline, with fernlike markings on the surface, and very brittle, so that it may be easily powdered; its specific gravity is 6.72; it melts at 450° C., and volatilises at a higher temperature. It does not oxidise at ordinary temperatures, but when heated in air, antimonious oxide Sb2O is formed; and at a red heat antimony burns with a bluish-white flame producing dense white fumes of Sb2O3.

Antimony and sulphur readily unite when heated together, forming Sb,S,; the same compound is also formed by heating the oxide with sulphur, thus

Antimony unites with other metals to form valuable alloys, in consequence of its hardening properties, but it impairs the malleability and ductility of the malleable metals. The effect of even small quantities of antimony on the malleable metals, such as copper, gold, iron, etc., is most injurious, making them hard and brittle.