SILVER, is the whitest of metals, and next to gold the moat malleable and ductile. Under the hammer, the continuity of its parts is not destroyed until its leaves are not more than the one hundred and sixty thousandth part of an inch thick ; in this state it does not transmit light. Its specific gravity is 10.474. It continues melted at 280 of Wedgewood, but a greater heat is requisite to bring it into fusion. Its tenacity is such, that a wire of one-tenth of an inch in diameter will sustain a weight of 2701bs. without breaking. Silver has neither smell nor taste ; these properties, together with its brilliant whiteness, hardness, and tenacity, eminently adapt it to the uses of the table ; and when to these qualities is added its intrinsic value, its advantages as coin become obvious. Silver is not sensibly altered by the contact of air, unless containing sulphurous vapours it may be volatilized by an intense heat, and Lavoisier oxidised it by the blow-pipe and oxygen gas. By exposing silver twenty times successively to the heat of a porcelain nuance, Macquer is said to have converted it into a green-coloured glass. Although silver is found in almost all countries that contain mines, the greatest quantities are obtained from the mines of Mexico and Peru. The celebrated mine of Potosi, situated near the source of the Rio de la Plata, is one of the most considerable mountains of Peru, and this mountain is described by travellers as filled with veins of silver from the to to the bottom. Silver is often found native, in ramifications, consisting of octahedrons inserted into each other ; also in small intertwined threads, and in masses ; but it is moat commonly found in combination with sulphur. silver forms alloys with moat of the metals. Copper is the metal with which it is alloyed for the purpose of coinage. The British coinage contains 11 ounces 2 dwts of fine silver in the pound troy ; the copper stiffens the silver, increases its elasticity, but renders it less ductile. The alloy of silver and zinc is granulated on its surface and very brittle. Tin also, in the smallest quantities, deprives silver of its malleability. Alloyed with lead, silver ceases to be sonorous and elastic. Fine filings of silver, triturated with mercury in a warm mortar, form an amalgam, which by fusion and slow cooling affords tetra hedral prismatic crystals, terminated by pyramids of the same form. The mercury cannot be separated from the silver, except by a much stronger heat than would be required to volatilize it alone.
Sulphuric acid, if concentrated and boiling,•will dissolve silver in a state of minute division. The nitric acid, a little diluted, has a powerful action upon silver, of which it will dissolve half its weight. The solution is at first blue ; this colour disappears when the silver is pure, but becomes green if it contains copper. If the silver contains gold, this metal separates in blackish-coloured flocks. The solution is extremely corrosive, and destructive to animal sub stances. When the acid is fully saturated, it deposits crystals as it cools, and also by evaporation. These crystals are called lunar nitre, or nitrate of silver. By fusion, for which a gentle heat is sufficient, their water of crystallization is driven off, and also a part of the acid, by which they become a subnitrate ; this forms the Iris infernalis, or lunar caustic of the surgeons; it is of a black colour, and usually cast in the form of small sticks. A heat but little above what is necessary for fusing the nitrate, separates the whole of the acid, and the silver is revived. Lunar caustic should be made of silver entirely free from
copper, as the copper is poisonous to wounds. The cauticity of this and all other mineral solutions, is attributed to the strong propensity _of the metal to assume the metallic state; in consequence of which, it readily parts with its oxygen to substances it is in contact with, and therefore such substances as are capable of receiving the oxygen, virtually undergo combustion. A solution of nitrate of giver in water is perfectly free from colour ; but it stains the slun, and all animal and vegetable substances, an indelible black. It is employed in a weak state to dye the human hair, and when mixed with a little gum-water, forms a permanent ink for marking linen. It is also employed for and other stones. Nitrate of silver is a most powerful antiseptic ; a 12,000th part of it, dissolved in water, will render the water incapable of putrefac tion, and it may be separated at any time by adding some common salt. Silver is precipitated from its solution in nitric acid by muriatic acid, in the form of a white curd, which, when fused, forms a semi-transparent, and rather flexible mass, re sembling horn ; it was therefore anciently called lima cornia, or horn silver, and is supposed to have given rise to some of the accounts we have of flexible glass ; it is a muriate of silver, soon blackens in the air, and is scarcely soluble in water. The muriatic acid does not dissolve silver, but has a strong affinity for its oxide; and as the muriate of giver is not very soluble in water, the nitrate of silver is employed as a re-agent, to discover the presence of muriatic acid in any liquid ; for if it contain that acid, muriate of silver will fall down in a cloud, on dropping nitrate of silver into it. The nitric acid sold in the shops generally contains mnriatic or sulphuric acid, or both ; hence the nitrate of silver is employed to free the nitric acid from the two latter acids. For this purpose, nitrate of silver is poured into it by degrees, until no more precipitate is produced; after which it is rendered dear by filtering.. Nitric acid, thus purified, is called by artists precipitated aqua-fortis; but it still contains some diver, from which it cannot be freed, except by distillation. When mercury is added to the nitric solution of silver, a precipitation of the silver is formed, which, from its resemblance to vegetation, is called arbor Diana, or tree of Diana. A few drops of nitrate of silver, laid upon glass, with a copper wire in it, afford another beautiful preci pitation of the silver, in the form of a plant. Silver supplies a fulminating powder, incomparably more energetic than any other ; the nitrio solution of fine silver is precipitated by lime-water ; the water is decanted, and the oxide le exposed for two or three days to light and air. This dried oxide, being mixed with ammonia, or volatile alkali, assumes the form of a black powder ; decant the fluid, and leave the powder to dry in the open air, thispowder is the ful minating silver, which, after having been once made, can no longer be touched, as the slightest agitation causes it to detonate ; it must therefore be left in the vessel in which the evaporation was performed ; it should never be made but in minute quantities, and not more than the fulmination of a grain should be attempted at once.