very soluble in water, and its solution evolves vapor of osmic acid at the ordinary temperature. Its acid properties are feeble, it neither reddens litmus nor decomposes the carbonates; its salts are unstable.

OSMIUM AND CHLORINE.-When osmium is heated in a current of chlorine, a chloride and a bichloride are obtained; the former, being less volatile, condenses near to the osmium, whilst the latter is carried to a greater distance.

The (proto-) chloride has a green color, and is soluble in water, but the solution speedily decomposes, with precipitation of metallic osmium, bydrochloric and osmic acids being produced.

The bichloride has an orange-yellow color, is crystalline, very fusible, and deliquescent.

The name of osmium has been derived from osun, odor, in consequence of the powerful odor of osmic acid.

REACTIONS OF OSMIUM (Binoxide).—The alkalies and their carbonates ; after some time or on boiling, a black precipitate.

Hydrosulphuric acid and sulphide of ammonium; brownish-yellow precipitate. Subnitrate of mercury; yellowish-white precipitate.

Chloride of tin; brownish precipitate.

All compounds of osmium, when boiled with excess of nitric acid, evolve the peculiar odor of osmic acid.

RUTHENIUM.

Sym. Ru. Eq. 52.2. Sp. Gr. 8.6.

§ 281. Ruthenium exists in native platinum, alloyed with osmium and iridium. Preparation. In order to extract it, the alloy is powdered, mixed with chlo ride of sodium, and heated to redness in a current of moist chlorine; the mass is extracted with water, and a few drops of ammonia added to the solution, which is then gently heated; a red-brown precipitate is thus obtained, which is a mixture of the oxides of ruthenium and osmium. This precipitate is boiled with concentrated nitric acid, to dryness, when all the osmium is volatilized in the form of osmic acid; the residue is fused in a silver crucible with a mixture of potassa and nitre, and the fused mass digested in a closed flask with cold water free from air; after several hours, the supernatant liquid is decanted, and neutralized with nitric acid, when a black precipitate of sesquioxide of ruthenium is obtained; this precipitate may be washed and heated in a current of hydrogen, to obtain the metal.

Ruthe

Properties.-Ruthenium much resembles iridium; it is brittle, infusible, and scarcely affected by aqua regia. Its spec. grav. is said to be only 8.6. nium is oxidized when heated to redness in air; it forms four oxides.

The Oxide (RuO) obtained by heating the chloride with carbonate of soda in a current of carbonic acid, and washing the residue with water, is a dark gray powder with metallic lustre; it is insoluble in acids, and is reduced by hydrogen at the ordinary temperature.

The Sesquioxide (Ru,O,) is of a dark brown color; it is insoluble in water. and alkalies, but dissolves in acids, giving yellow solutions. These produce, with sulphuretted hydrogen, a brown precipitate of sesquisulphide of ruthenium, the supernatant liquid having a blue color."

Binoxide of Ruthenium (RuO,) is obtained by boiling the scsquisulphide with nitric acid, and decomposing the sulphate of binoxide thus obtained with

an alkali. By calcining the precipitated hydrate, the binoxide is obtained as a greenish-blue powder of metallic appearance.

Ruthenic Acid (RuO,) is only known in combination with bases; rutheniate of potassa is obtained when either of the oxides of ruthenium is heated with nitrate of potassa; it is soluble in water, yielding a yellow solution, from which the acid may be momentarily isolated by adding a stronger acid, but is soon decomposed into binoxide of ruthenium and oxygen.

Chloride of Ruthenium, RuCl, obtained by heating the metal in a current of chlorine, is black, crystalline, insoluble in water and acids.

Sesquichloride of Ruthenium, Ru,Cl,, is formed by dissolving the hydrated sesquioxide in hydrochloric acid, and evaporating to dryness; it has a bluishgreen color, and is soluble in water; the aqueous solution yields, with the chlorides of potassium and ammonium, dark brown crystalline precipitates, which are double chlorides.

The bichloride, RuCl,, is only known in combination with chloride of potassium.

REACTION OF RUTHENIUM (Sesquioxide).-The alkalies and their carbonates; brown precipitates, soluble in excess.

Hydrosulphuric acid and sulphide of ammonium; dark brown precipitate. Chlorides of potassium and ammonium; dark brown crystalline precipitates. Cyanide of mercury; blue precipitate, and blue solution.

Nitrate of silver; black precipitate, which becomes lighter on standing, the supernatant liquor acquiring a rose color.

We have now concluded the description of the group of metals found in the ores of platinum, viz. platinum, palladium, rhodium, iridium, osmium, and ruthenium, and it cannot fail to have been observed that a remarkable similarity exists between these metals in their infusibility, and in the disposition of their chlorides to form double-salts with the chlorides of the alkali-metals.

Moreover, a striking coincidence is observed in their equivalents, by which we are enabled to subdivide them into two classes, the first comprising

The differences, it will be perceived, are in all these cases so slight, that probably, were errors of analysis left out of the question, they would actually disappear.1

ANALYSIS OF THE ORES OF PLATINUM.

§ 282. The complete analysis of the ores of platinum is an operation of such a complicated character, that it would be impossible to describe it here with all the details necessary for its successful execution. We shall therefore content ourselves with giving a general outline of the method adopted, which although of little practical utility, possesses great interest in the eyes of the scientific

1 This remarkable circumstance would suggest a connection between these metals similar to that pointed out at p. 152, between other analogous elements.

chemist, as one of the best examples of elaborate analysis with which we are acquainted.

The ores of platinum generally contain, besides that metal,

It is our intention merely to point out the methods of separating and estimating the rarer metals in this list.

About 30 or 40 grains of the ore are dissolved in aqua regia, in a small retort, to which a carefully-cooled receiver is attached. The distillation is continued until the liquid becomes syrupy, and solidifies on cooling. The saline mass is dissolved in the smallest possible quantity of water, and the solution carefully decanted into another vessel. The distilled acid is poured back on to the undissolved residue, and the distillation carried on to the same point as before.

The distillate, which contains the osmium, is diluted with water, and nearly neutralized with ammonia. It is poured into a flask, diluted so as nearly to fill it, and thoroughly saturated with sulphuretted hydrogen; after which the flask is closed with a cork, and set aside for a day or two, till the precipitate has completely separated, leaving the solution clear. The clear liquid is drawn off with a siphon, the sulphide of osmium collected upon a weighed filter, washed, dried, and weighed.

The solution in the retort, and that previously poured out, are mixed together, and filtered off from the residue, which contains a little osmide of iridium, sand, &c., which should be weighed.

The filtered solution is mixed with twice its volume of alcohol of sp.gr. 0.833, and a strong solution of chloride of potassium added, as long as it produces any precipitate, which consists of the potassio-chlorides of platinum and iridium, together with small quantities of the corresponding compounds of rhodium and palladium. The precipitate is collected upon a filter, and washed with alcohol of 60 per cent., mixed with a small quantity of a strong solution of chloride of potassium, until the washings are no longer precipitated by sulphuretted bydrogen.

The precipitate is then dried, mixed with its own weight of carbonate of soda, and heated in a porcelain crucible till the mixture has become black throughout, when the platinum has been reduced to the metallic state.

The mass is washed with water, and when the greater part of the saline matter had been thus removed, the residue is treated with dilute hydrochloric acid, to dissolve the remainder of the alkali, collected on a filter, washed, dried, ignited, and weighed. Its weight represents that of the metallic platinum, together with the sesquioxides of iridium and rhodium. This residue is now fused with five or six parts of bisulphate of potassa, in a platinum crucible. The mass is treated with water, the residue (platinum and sesquioxide of iridium) ignited and weighed.

The solution, containing the rhodium, is mixed with an excess of carbonate of soda, evaporated to dryness, and the residue ignited in a platinum crucible.

The ignited mass is treated with water, when sesquioxide of rhodium remains undissolved; it is collected on a filter, washed, ignited with the filter, and reduced by hydrogen.

The mixture of platinum and sesquioxide of iridium is digested with very dilute aqua regia, to remove the platinum. The mixture is allowed to subside, the clear liquid decanted, strong aqua regia, mixed with some chloride of sodium, poured over the residue, and the whole evaporated to dryness (the chloride of sodium is added to convert the bichloride of platinum into a double chloride,

and thus to prevent the formation of any (proto-) chloride). The mass is washed, in a filter, with a dilute solution of chloride of sodium, afterwards with dilute chloride of ammonium, dried, and ignited. The iridium is reduced by hydrogen, and weighed. The small quantity of iridium contained in the solution is recovered by adding an excess of carbonate of soda, evaporating and igniting. The residue is washed with water, the platinum removed by aqua regia, the residual sesquioxide of iridium washed, dried, reduced by hydrogen, and weighed; its weight is then added to that of the iridium previously obtained. The amount of the platinum is obtained by difference.

The alcoholic liquid filtered from the double chlorides of platinum, iridium, and rhodium, is poured into a flask, perfectly saturated with sulphuretted hydrogen, the flask closed, and allowed to stand for twelve hours in a warm place. The solution is then filtered, and the alcohol evaporated, any additional precipitate being added to the former one.

The precipitate contains chiefly the sulphides of palladium, iridium, and rhodium; a little iridium and rhodium also remaining in the filtrate.

The sulphides are roasted in a platinum crucible as long as any sulphurous acid is evolved; the residue is treated with concentrated hydrochloric acid, which dissolves a basic sulphate of binoxide of palladium (together with a basic sulphate of copper), leaving the sesquioxide of rhodium and iridium, together with a little platinum.

The hydrochloric solution is mixed with chloride of potassium and a little nitric acid, and evaporated to dryness. The residue is dissolved in boiling water, and the palladium precipitated as cyanide, by solution of cyanide of mercury; the cyanide of palladium, when ignited, leaves the metal.

The residue left by hydrochloric acid is fused with bisulphate of potassa, the mass washed with water, treated with aqua regia to remove a little platinum, and the oxide of iridium which is left may be reduced and weighed.

The rhodium in the solution of bisulphate of potassa may be determined ac cording to the directions given above.

The original filtrate from the precipitate produced by sulphuretted hydrogen is heated with nitric acid to peroxidize the iron, which is then precipitated by ammonia, washed, dried, ignited, and weighed. Since it contains a little iridium and rhodium, it must be reduced by hydrogen, and dissolved in ydrochloric acid, when those two metals are left; they are converted into sesqi oxides by ignition in the open air, and weighed.

The filtrate from the sesquioxide of iron, which still contains iridium and rhodium, is mixed with excess of carbonate of soda, evaporated to dryness, and the residue heated to dull redness; it is afterwards treated with water, which leaves the sesquioxides of iridium and rhodium undissolved. These may be mixed with the sesquioxides obtained above, and separated, as usual, by fusion with bisulphate of potassa.

TIN.

Sym. Sn. Eq. 58. Sp. Gr. 7.285.

§ 283. This metal and its compounds deserve a considerable share of our attention, since they are applied to a great many useful purposes. Tin is not met with in commerce in a state of purity; commercial tin generally contains traces of lead, iron, copper, arsenic, and, sometimes, antimony, zinc, bismuth, molybdenum, tungsten, and manganese. In order to obtain perfectly pure tin,

the ordinary metal is granulated, and dissolved in hydrochloric acid, and the solution concentrated by evaporation. It is allowed to cool in a beaker, and carefully covered with a layer of water; a plate of tin is then introduced, so as to traverse the two layers of liquid, when a feeble galvanic current will be excited, and the pure tin will be deposited in fine crystals.

Properties. Tin is a white metal, with a very faint tinge of yellow. It is one of the softest and least elastic metals. The malleability of tin is very considerable, but, with the exception of lead, it is the least tenacious of common metals, for a wire of one-tenth of an inch in diameter will support only forty-seven pounds. Tin has a great tendency to crystallize, and the ordinary forms of this metal have a remarkably crystalline texture, as may be shown by rubbing the surface with warm diluted nitro-hydrochloric acid, when it assumes a peculiar diversified appearance, which is termed the moiré métallique, and is due to the unequal reflection of light by the facets of the crystals. When a bar of tin is bent, a peculiar crackling sound is heard, caused by the friction of the crystals upon each other.

The fusing point of tin is 442°.4 F. (228° C.). It is very slightly volatile, even at the highest temperatures. When fused tin is allowed to cool gradually, it crystallizes in octohedral prisms. If, when in the fused state, it be poured into a warm iron mortar, and stirred continually till it cools, it may be reduced to powder.

Tin is not altered by exposure to air at the ordinary temperature; when fused in air, it becomes covered with a gray film, containing both oxide and binoxide of tin, and, at a white heat, it burns in air, being entirely converted into the binoxide. It is also capable of decomposing steam at a red heat, binoxide of tin being produced, and hydrogen evolved.

Very strong nitric acid does not act upon tin, but when a little water is added, the metal is very rapidly oxidized (with evolution of binoxide of nitrogen), and converted into metastannic acid, Sn,O10, which is insoluble in water and in nitric acid, so that no tin is found in solution.

When tin is treated with moderately strong nitric acid, it is oxidized partly at the expense of the water, the hydrogen of which, in the nascent state, acting upon the excess of nitric acid, or upon one of the inferior oxides of nitrogen, gives rise to the production of ammonia, and hence nitrate of ammonia is always found in the nitric solution of alloys containing tin.

Tin dissolves slowly in cold or dilute hydrochloric acid, but much more rapidly in the hot concentrated acid, hydrogen being evolved, and (proto-) chloride of tin formed. It has been found that hydrochloric acid holding a quantity of chloride of tin in solution, attacks the metal much less readily than the pure acid, whence arises the difficulty which is experienced in dissolving a quantity of tin entirely in one and the same portion of hydrochloric acid.

Dilute sulphuric acid dissolves tin slowly with the aid of heat, hydrogen being evolved; but the hot concentrated acid rapidly converts this metal into sulphate of the (prot-) oxide, with evolution of sulphurous acid.

The hydrates of potassa and soda act upon tin, at high temperatures, hydrogen being evolved, and a soluble compound of the alkali with metastannic acid produced.

Fused nitre is also capable of oxidizing tin. This metal combines directly, and often very energetically, with chlorine, sulphur, phosphorus, &c. It also forms alloys with many of the metals.