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A few of the metals resist the action of heat and air so completely, that they may be kept in fusion in an open crucible for many hours without undergoing change. This is the case with gold and silver, and a few others; hence they were called perfect or noble metals: they may, however, be oxidized by the Voltaic flame; or by passing a strong electric discharge through them, when drawn into very fine

wire.

Other metals readily absorb oxygen when exposed to a temperature approaching a red heat; as iron, mercury, nickel, &c.; others absorb it when in fusion, as lead, tin, antimony, &c.; others at lower, or even at common temperatures, as arsenic, manganese, sodium, potassium, &c. That the metals have very different attractive powers in regard to oxygen is also shown by the circumstance of one metal being frequently oxidized at the expense of another; thus the oxide of mercury, heated with metallic iron, produces metallic mercury and oxide of iron; potassium, heated with oxide of manganese, becomes oxidized, and metallic manganese is obtained.

Some of the oxides are decomposed by mere exposure to heat, as those of gold, mercury, &c.; others require the joint action of heat, and some body having a high attraction for oxygen, such as charcoal. Thus when oxide of lead is heated with charcoal, carbonic acid gas is evolved, and metallic lead obtained.

Each metal has a certain definite quantity of oxygen with which it combines; and were the same metal unites in more than one proportion with oxygen, in the second, third, and other compounds, it is a multiple of that in the first, consistent with the law of definite proportions (46). Thus 100 parts of mercury combine with 4 of oxygen to produce the protoxide, and with 8 to produce the peroxide. Copper also forms two oxides; in the one 12.5 of oxygen are united to 100 of metal, and in the other 25.

Among the combinations of metals with oxygen, some are insoluble in water, or nearly so, and have neither taste nor smell; others are soluble and sour, constituting the metallic acids: others are soluble and alcaline, forming the fixed alcalis and alcaline earths. They are of all colours, and frequently the same metal united to different proportions of oxygen produces compounds differing in colour: thus we have the black and red oxide of mercury, the white and the black oxide of manganese, &c.

515. Action of Chlorine. All the metals appear susceptible of com- Action of chi bining with chlorine, and of producing a class of compounds which rine. may be termed metallic chlorides.

There are a few of the metals which resist the action of chlorine at common temperatures, but when heated they all combine with it; some slowly, others rapidly and with intense ignition. Copper leaf, powdered antimony, arsenic, &c., burn when thrown into the gas: mercury and iron inflame when gently heated in it; silver, gold, and platinum quietly absorb.it.

The attraction of chlorine for metals is greater than that of oxygen; consequently, when a metallic oxide is heated in chlorine, oxygen is evolved, and a chloride formed. The insoluble chlorides are also formed by adding solution of chlorine, or of the soluble chlorides, or of muriatic acid, to the soluble metallic salts. Thus chloride of silver,

Action of chloric acid.

which is insoluble, is thrown down from the soluble nitrate of silver by solution of chlorine, of muriatic acid, and of common salt.

The physical and chemical properties of the chlorides are extremely various. They are nearly of all colours. Some are unchanged by heat; others undergo decomposition. Some are soluble, others insoluble, in water. Several of them decompose water, giving rise to the formation of muriatic acid, and an oxide; or in some cases to a muriate. The same metal often forms more than one compound with chlorine, and these compounds are designated as the oxides. Thus we have the protochloride and perchloride of mercury, &c.

Many of the metals decompose muriatic acid in which case hydrogen is evolved, and a metallic chloride produced; and when metallic oxides are heated in muriatic acid, they generally give rise to the formation of a chloride and water.

516. Action of Chloric Acid. The compounds of the metallic oxides with chloric acid are decomposed by heat with the copious evolution of oxygen, and a chloride generally remains: some of these salts have been long known, others only recently investigated. The oxychlorates have been scarcely examined.

Action of lo- 517. Action of Iodine. Iodine aided by heat acts upon many of the

dine.

metals, and produces metallic iodides. Some of these are soluble in water without decomposition; others decompose water and produce hydriodates; others are insoluble. The insoluble iodides may generally be formed by adding a solution of iodine or of hydriodic acid to the soluble metallic salts.

Iodine often combines in more than one proportion with metals, forming a protiodide and a periodide.

518. Action of Iodic Acid. The compounds of this acid with the Action of lo metallic oxides have been but little examined: they are decomposed by heat, sometimes with the evolution of oxygen only; at others, iodine is also given off.

Action of hy

drogen.

Action of wa

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519. Action of Hydrogen.-Hydrogen forms permanent compounds with two of the metals only, namely, arsenic and tellurium. It appears to combine with each in two proportions, forming two solid compounds, the hydrurets or hydrogurets of arsenic and tellurium; and two gaseous compounds, arsenuretted and telluretted hydrogen. At high temperatures it dissolves potassium, forming potassiuretted hydrogen gas.

There are many of the metallic oxides, and a few of the chlorides, which are decomposed by hydrogen: the oxides are reduced with the formation of water, and the chlorides with the production of muriatic acid.

520. Action of Water. -Those metals which are speedily acted upon by common air and oxygen, are also generally susceptible of decomposing water; some of them rapidly, others slowly. There are some metals which are not acted upon by air deprived of moisture, nor by water deprived of air; but moist air, or water containing air, effect their oxidizement: this appears to be the case with iron. - Dr. MARSHALL HALL. Quarterly Journal, vii. 55.

Water combines with some of the metallic oxides, and produces hydrated oxides, or metallic hydrates. In these the relative proportion of water is definite. Some are easily decomposed by heat, as hydrate of copper; others retain water even when heated to redness, as hy drate of potassa..

Action of ni

21. Action of Nitric Acid. - As no metal is soluble in an acid except in the state of oxide, and as the greater number of metals are tric asid. capable of decomposing nitric acid, and of resolving it into some of the other nitric compounds, nitric acid is a very generally acting solvent of these bodies. It dissolves all the metallic oxides and produces a numerous class of nitrates, which if prepared with heat and with excess of acid, generally contain the metal at its maximum of oxidizement. The nitrates are all decomposed by a red heat; they give off oxygen and nitrogen, either separate, or combined, and the metallic oxide remains. They are also decomposed when heated with sulphur, phosphorus, or charcoal; and sulphurous, phosphoric, and carbonic acids are formed; the phosphoric, being a fixed acid, remains united to the metallic oxide; while the sulphurous and carbonic acids are usually expelled. The nitrates are decomposed by sulphuric acid, nitric acid is evolved, and sulphates are formed.

In the neutral nitrates the proportion of oxygen in the acid is to that in the base as 5 to 1. Thus in the nitrate of potassa 48 parts of potassa, containing 8 of oxygen, are combined with 54 of nitric acid, containing 40 of oxygen; and in the pernitrate of copper, 80 parts of peroxide of copper containing 16 of oxygen, are combined with 108 of nitric acid, containing 84 of oxygen.

522. Action of Ammonia. At high temperatures some of the metals are capable of decomposing ammonia. Liquid ammonia dissolves several of the metallic oxides, and with some of them forms crystallizable compounds. The compounds of ammonia with the oxides of gold, silver, and platinum, detonate when heated, and the oxide and the ammonia are both decomposed.

523. Action of Sulphur.-All the metals appear capable of forming Action of sulsulphurets. These are in some cases formed by heating the metal with phur. sulphur; in others, by decomposing the sulphates; and in others, by the action of sulphuretted hydrogen. The sulphurets are in general brittle; some have a metallic lustre; others are without lustre. Some are soluble, others insoluble in water. Where the same metal forms two sulphurets, the sulphur in those containing the largest proportion an exact simple multiple of the sulphur in those containing the smallest proportion. When the metallic sulphurets are heated some undergo no change, as those of sodium and potassium; others sublime unaltered as sulphuret of mercury; others lose a portion of their sulphur, and, if air be admitted, sulphurous acid escapes and the metal passes into the state of oxide, as sulphuret of lead; others again are entirely decomposed, the metal being completely reduced; this happens on heating sulphuret of platinum or of gold. It is doubtful whether any definite compounds of sulphur with the metallic oxides exist.

524. Hyposulphurous acid combines with the metallic oxides and produces a class of salts termed hyposulphites. Several of these have been examined by Mr. Herschel (Edinburgh Philosophical Journal, i.) In some of their characters they resemble the sulphites: they are easily soluble; of a bitter or sweet taste; and decomposed by a heat below redness, and by almost all other acids. Their solutions readily dissolve chloride of silver.

525. Sulphurous acid combines with many of the metallic oxides, producing sulphites; in some instances oxygen is transferred from the Sulphites. eride to the acid, and sulphates result.

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The sulphites are soluble in water, and have a sulphurous taste and smell. Exposed to moist air, they absorb oxygen, and pass into the state of sulphates. They are decomposed by sulphuric acid, which expels sulphurous acid, and the salts are converted into sulphates. When perfectly pure they are not affected by solution of baryta.

526. Hyposulphuric acid forms with the metallic oxides a class of hyposulphates which have been very imperfectly examined. They do not afford precipitates with solution of baryta.

Sulphates.

527. Sulphuric acid, in its concentrated state, is acted upon by a few of the metals only; when diluted, some of them are oxidized at the expense of the water, hydrogen is evolved, and the metallic oxide combines with the acid, producing a sulphate. In these cases the hydrogen evolved is the indicator of the quantity of oxygen transferred to the metal; every volume of hydrogen is the equivalent of half a volume of oxygen, and accordingly the production of 100 cubic inches of hydrogen, indicates the transfer of 50 of oxygen, or by weight of about 17 grains. As different metals unite to different weights of oxygen, they will obviously evolve different quantities of hydrogen. Thus, if one metal, to become soluble in sulphuric acid, require to be united with 15, and another with 30 per cent. of oxygen, the latter will evolve twice the volume of hydrogen, compared with the former.

Sulphuretted hydrogen.

As the evolution of hydrogen, during the solution of a metal in dilute sulphuric acid, is referable to its oxidizement, no hydrogen will be evolved by the action of the acid upon an oxide, but it will be merely dissolved.

The sulphates are an important class of salts. The greater number of them are soluble in water, and the solutions are rendered turbid by solutions of baryta. They are all decomposed at a red heat by charcoal, and most of them are thus converted into sulphurets; carbonic acid, and carbonic oxide, being at the same time evolved.

In the neutral sulphates the proportion of oxygen in the acid is to that in the base as 3 to 1. Thus sulphate of soda is composed of 32 soda containing 8 of oxygen, combined with 40 of sulphuric acid containing 24 of oxygen.

528. Action of Sulphuretted Hydrogen. It seems doubtful whether any of the metals combine with sulphuretted hydrogen. It unites with several of their oxides, and forms hydrosulphuretted oxides. Many of these compounds are insoluble, and may be formed by adding a solution of sulphuretted hydrogen, or of hydrosulphuret of ammonia, to solutions of the respective metallic salts. Sometimes, however, a decom position is effected in these cases, both of the sulphuretted hydrogen and of the oxide, and a metallic sulphuret is formed, the hydrogen combining with the oxygen of the oxide to form water, and the sulphur uniting to the metal. In a few cases the metallic oxide is reduced The following table shows the effect of sulphuretted hydrogen and of hydrosulphuret of ammonia upon solutions of several of the metals, as far as colour of the precipitate is concerned.

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