Preparation. Mercury occurs in nature united with sulphur in the form of cinnabar (Hg S), a red mineral in acute rhomboids and regular 6-sided prisms. The sulphur is removed by distilling the cinnabar with lime or iron filings in iron retorts; the mercury is allowed to condense in vessels filled with water, sulphuret of calcium and SO, being formed. In Spain it is re. duced in a peculiar furnace without any addition, by bringing the flame in contact with the hot ore; the sulphur is converted into (S O2) sulphurous acid.

Amalgams are compounds of mercury with other metals. Alloys are compounds of all other metals except mercury. Mirror or Tin Amalgam, used in silvering the backs of looking-glasses, consists of 3 parts mercury and I tin. Fluid Amalgam is formed of 3 mercury, 1 lead, and 1 bismuth. These metals are sometimes used to adulterate mercury; but when so mixed, its drops are not spherical, but drag a tail. Amalgam for electric machines, consists of 1 zinc, 1 mercury, 4 tin.

Suboxide (Hg2 O), Dinoxide, Black oxide, Ethiops per se, Mercury of Moscati. Mercury tarnishes by exposure to air. When calomel is precipitated by soda or potash, the black oxide falls (Hg, Cl and Na O becoming Hg, O and Na Cl). Lime water has the same action, and thus forms what is called in medicine black wash, which is used for sores. Specific gravity 10'69: forms salts with acids, which are generally colourless; precipitated black by NaO.

Oxide (Hg 0 13.5), Red Precipitate, Red Oxide, Deutoxide, Binoxide, Peroxide. — In regular red octahedrons, red powder, or in red scales; formed by heating mercury to 600° in the open air or by heating the nitrate; taste acid and disagreeable: when pure, it gives off no coloured fumes. Specific gravity 11; becomes black by heating, setting zinc and tin on fire; used in surgery as a caustic to clean sores. Its salts are colourless or yellow, and poisonous; NH, digested on Hg forms a yellow powder or a hydrate of an amide and oxide of mercury (Hg N H2, 2 Hg O 3H 0). Lime-water throws down the yellow oxide and forms the surgical yellow wash (Hg Cl, Ca O forming Hg O, and Ca Cl). The yellow precipitate is HgOHO or hydrate, and becomes red by heat.

Subchloride (Hg, Cl 29.5), Dichloride, Protochloride.— Calomel, Sweet Mercury. Mercury absorbs chlorine and forms calomel, which may be sublimed in white 4-sided prisms, or as a white powder. Specific gravity 7.175. The usual process for making it consists of three stages: 1. Sulphate of mercury is formed by boiling 12 mercury with 15 sulphuric acid (Hg and 2SO, becoming HgO SO, and SO, evolved); 2. Each atom, or 18 grains, of sulphate are then triturated in a mortar with 12 of mercury, and 7 of common salt (Na Cl). 3. This mixture being placed in

a flask and heated, the calomel sublimes (Hg O SO,, Hg and Na Cl becoming Hg, Cl and NaO SO,). This experiment may easily be made by heating a small flask, which is to be supplied with a perforated cork and a short tube passing through it, set in a small sand-bath over a gas or spirit lamp. Calomel is soluble in 12,000 parts of water, tasteless, not poisonous; but is speedily in part converted in the stomach into corrosive sublimate, which is a poison. When ammonia is added to calomel, a gray precipitate is formed, consisting of Hg, Cl, Hg, NH2. It is formed at the expense of 2 atoms of calomel and 2 of ammonia (2Hg, Cl and 2NH, becoming Hg, Cl, Hg, NH, and NH, HCl); gray precipitate and muriate of ammonia being formed. By heating with chlorides, calomel is converted into corrosive sublimate; hence its action in the system.

Chloride (Hg Cl. 17). — Corrosive Sublimate, Bichloride, Perchloride. Fine white semitransparent mass of prisms, cubes, or rhomboids, or white powder, soluble in 18 parts of cold and 2 of hot water. Specific gravity 5.139. Taste acrid and caustic; virulent poison, uniting with and destroying live organic substances, but preserving them when dead. Hence it is used to keep anatomical preparations and for embalming dead bodies. The usual process for preparing it consists of three stages: 1. A sulphate of mercury is prepared by heating cautiously in a basin or flask equal parts of sulphuric acid with mercury until the mercury disappears; the addition of a little nitric acid facilitates the operation (2SO, and Hg becoming Hg OSO,, and SO, evolved); 2. 18 parts of the sulphate are triturated in a mortar with 7 parts of common salt (Na Cl); 3. The mixture is introduced into a flask with a perforated cork and tube, as with calomel, and sublimed; the action being as follows: sulphate of mercury, common salt (Hg O SO,, and Na Cl), form corrosive sublimate, Glauber salt (Hg Cl and NaO SO,). Corrosive sublimate may be crystallised in large prisms by solution in water and slow evaporation; it dissolves in alcohol and ether, and sublimes entirely; it dissolves in H Cl; and on the addition of protochloride of tin, a black precipitate of finely divided mercury falls, which becomes running mercury by heat. Iodide of potassium gives a scarlet precipitate. A plate of copper becomes brown in its solution. When swallowed, it produces a pain in the stomach and bowels diarrhoea and vomiting. The antidotes are white of egg, milk, and iron filings, the two former combining with it, as may be proved by adding a solution of corrosive sublimate to a solution of white of egg.

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White precipitate (Hg Cl, Hg NH2) is formed by adding NH, to a solution of corrosive sublimate: 2Hg Cl and 2NH, become Hg Cl Hg NH, and NH, HCl. When boiled with water it becomes a yellow powder (2Hg Cl+Hg NH2), and 2HO become

Hg Cl, Hg NH, HgO and NH, HCl. When boiled with NaO white precipitate gives out NH, and does not become black as calomel does.

Black sulphuret, Disulphuret (Hg, S).- Black powder obtained by precipitating the subnitrate with sulphohydric acid (SH).

Sulphuret or Red Sulphuret (HgS). · Cinnabar, Vermilion, occurs in nature, but may be prepared artificially by fusing 1 part of sulphur with 6 mercury, and subliming the blackish red mixture in a covered crucible, occasionally removing the lid and stirring it.

Subiodide (Hg, I 40.75), Diniodide.-Yellowish green powder, formed by dropping an iodide into a solution of the subnitrate of mercury, or by rubbing in a mortar 25 parts of mercury with 153 parts iodine, with some alcohol.

Iodide (HgI 28 25). — Scarlet crystalline powder, formed by adding iodide of potassium to corrosive sublimate, or by rubbing in a mortar 12 parts Hg with 15.75 I, with the aid of alcohol, so as to form a red powder, which is to be boiled with a strong solution of common salt until it dissolves. On cooling it deposits in fine carmine scales. Slightly soluble in water, very soluble in iodide of potassium. Specific gravity of its vapour 15 68. Becomes a yellow fluid at 400°. Both of these iodides are used in medicine, internally and in the form of ointment.

Cyanide of Mercury (Hg Cy 15.75).-Square prisms prepared by dissolving 2 parts yellow prussiate of potash in 15 boiling water, adding 3 parts dry sulphate of mercury, boiling for 15 minutes, filtering while hot, and crystallising out the cyanide. Additional crystals may be obtained from the mother liquor. It is used for preparing Cyanogen (p. 81), and is poisonous.

Sulphate of Mercury (HgO SO,) is formed in the process for calomel. When boiled with water, it becomes yellow, being converted into Turbith mineral (3HgO SO3). Subnitrate of mercury, (Hg2O NO, 2HO). - Colourless prisms formed by dissolving mercury in cold dilute nitric acid. Nitrate of mercury (2HgO NO, 2HO) is obtained by dissolving mercury in hot nitric acid.

Estimation of Tin, Bismuth, and Mercury. · Tin is best estimated by treating it either in the metallic or compound state, with an excess of NO, evaporating to dryness, treating with water and filtering. The deutoxide remains: every 9 grains of which contain 74 of tin. Bismuth is usually precipitated by carbonate of NH,, having previously removed all HCl by evaporation, and substituted NO. Mercury is separated by dissolving in HCl, and adding protochloride of tin in a small flask and boiling, and after the appearance of globules, pouring into a porcelain crucible, washing, drying at a low heat, and weighing.

THESE metals require an intense heat to melt them. They are best dissolved by a mixture of NO, and H Cl: their oxides are reduced to the metallic state by heat, and they form but a limited number of combinations, their oxides especially showing no tendency to unite with acids.

A reddish yellow metal; crystallising in cubes, softer than silver; the most malleable and ductile body known: one grain can be drawn out in wire to 500 feet, and can be beat into gold leaf of 56 square inches. Specific gravity 19.3. Melts at 2015° F. : expands when fused, having a greenish colour, and contracts when cooling; in powder it is brown.

Gold occurs in nature in a free state, in the beds of rivers, mixed with sand, from which it is separated by washing. Sometimes it is mixed with silver, which can be dissolved out by means of sulphuric acid, the gold remaining unacted on. English gold coin contains 1 twelfth of copper. A sovereign weighs 123.274 grains, and contains 10.273 grains of alloy.

Gold amalgam is a compound of gold and mercury, employed for gilding metals. The metals are immersed in the amalgam until a combination is formed. The mercury is then dissipated by heating the metal; the dull gold is then brightened by polishing with a brush, termed burnishing. Jeweller's gold is an alloy of gold and copper with silver. Green gold used in jewellery is an alloy of 3 silver and 7 gold. When gold contains much copper, it is liable to tarnish, which may be removed by immersion in ammonia. Gold is deposited on other metals by electrotype; the gold is dissolved in aqua regia, the solution is evaporated in the waterbath to remove the excess of acid; the residue is dissolved in 130 times its weight of water, and 7 times its weight of bicarbonate of potash is added. In this mixture the metal to be gilt is immersed. Instead of the alkali, cyanide of potassium is now

employed, and the poles of a battery are introduced into the fluid, Gold is soluble in a mixture of nitric and hydrochloric acids, but not in any single acid.

Dinoxide, suboxide (Au, O 25·5).- Green powder obtained by precipitating the subchloride (Au, Cl.) by caustic soda. Sesquioxide (Au, О, 27·5).· Brownish powder easily decomposed by light; does not combine with acids, but forms feeble compounds with bases. It is formed by adding a slight excess of caustic magnesia to a solution of gold in nitro-hydrochloric acid; the oxide precipitates in union with magnesia; wash the precipitate; digest in nitric acid, which removes the magnesia, and leaves the oxide in the state of a hydrate, but it parts with the water at 212°. When heated with hydrochloric acid, sesquichloride is formed; an oxide is formed by passing a spark of electricity through gold leaf placed between two plates of glass; the gold burns, and leaves the trace of the spark; it burns also when exposed to the action of the battery: the oxide forms fulminating gold when digested with ammonia. Gold bas less affinity for oxygen than any other metal. Hence its value in retaining its colour without tarnishing.

Purple of Cassius. — A fine purple powder, a compound of gold and peroxide of tin, formed by adding to a solution of chloride of gold a solution of protochloride of tin. It is used as a pigment for glass and porcelain, and may be prepared by dissolving 1 part of grain tin in 9 of NO, diluted with 2 of water; 3 parts of common salt are added, as the addition of salts promotes the separation; and then 80 parts of water are added. The chloride of gold is then added in drops.

Sesquichloride (Au, Cl, 38).-Pale yellow needles formed by igniting gold leaf in chlorine gas, or by dissolving gold in aqua regia (a mixture of 1 NO, and 3H CI), evaporating away the excess of acid, and dissolving in water; the crystals are deliquescent, and form a yellow solution. Gold is precipitated in the metallic state from this solution by phosphorus, sulphate of iron, iron, zinc, copper, &c. oxalic acid, and the vegetable acids, and salts of the alkalies. Pure gold is often obtained by adding protosulphate of iron to this salt, and washing with dilute H Cl and water. This salt is used in the electrotype for gilding, as a caustic in surgery, as an application to cancerous surfaces, and also as an internal remedy in syphilis. Fulminating gold (Au, Cl, 2NH, HO), yellow brown powder, formed by precipitating sesquichloride by NH,. Subchloride (Au, Cl. 29).—Yellow mass, insoluble in water, obtained by heating the sesquichloride up to the melting point of tin. Converted by water into gold and sesquichloride.

Sesquisulphuret (Au, S. 30·5).— Formed by precipitating the sesquichloride by SH. It is a yellow powder, much employed