of its sulphide in sulphide of ammonium. In the analysis of a solution, it is better, before treating it with hydrosulphuric acid, to remove by hydrochloric acid those metals which form insoluble chlorides. Silver and subsalts of mercury are thus entirely, lead partially, precipitated. The chloride of lead is removed by boiling the precipitate in a large quantity of water. The chloride of silver and subchloride of mercury are separated by treatment with ammonia, which dissolves the chloride of silver, and blackens the subchloride of mercury; or they may be separated by aquaregia in the cold, which dissolves the subchloride of mercury, and leaves the chloride of silver undissolved. But, for the complete separation of mercury from lead and silver, it is better to ensure the presence of mercury only as mercuric salt, by boiling the solution with nitric acid. The silver can then be separated completely by hydrochloric acid. Or the silver may be separated from the mercury by cyanide of potassium, as follows. The solution is nearly neutralised with an alkaline carbonate, and cyanide of potassium added till the precipitate first formed is entirely redissolved: excess of nitric acid is then added, when all the silver is precipitated as cyanide, while cyanide of mercury remains in solution. Lead may also be separated from mercury by cyanide of potassium: the addition of nitric acid decomposes the cyanide of lead, forming nitrate, whence the lead may be precipitated by an alkaline carbonate: the cyanide of mercury is not decomposed, and remains in solution. Or the lead may be separated by means of sulphuric acid, which must be in excess, otherwise a basic sulphate of mercury may be precipitated with sulphate of lead. Or the solution may be evaporated to dryness with excess of hydrochloric acid, and the residue treated with alcohol, which dissolves the chloride of mercury, leaving the chloride of lead undissolved.

For the analysis of a mixture of oxide of mercury, cinnabar, and red lead, Wöhler gives the following process. By digestion with dilute nitric acid, the oxide of mercury and protoxide of lead are dissolved; the lead is precipitated from the solution by dilute sulphuric acid, and then the mercury by hydrosulphuric acid or chloride of tin. The residue is then treated on the filter with a

mixture of warm dilute nitric and oxalic acids, which dissolves out the binoxide of lead, and the residual cinnabar is washed, dried, and weighed.

Mercury is estimated either in the metallic state; as subchloride, Hg2Cl; or as sulphide, Hg2S. In the first case, the solution, which must not contain free nitric acid, is digested with chloride of tin, or phosphorous acid, the reduced mercury washed, dried without the application of heat, and weighed. In the dry way the operation is thus performed. About an inch of carbonate of calcium is introduced into the closed end of a combustion tube, then the mercury compound mixed with quicklime, then about. two inches of quicklime. The open end of the tube is bent down and inserted into a narrow-mouthed bottle containing water, the end of the tube just dipping into the water. The layer of quicklime is then heated to redness, then the mercury-compound, and finally the carbonate of calcium, when carbonic anhydride is evolved, and sweeps all the mercury-vapour into the receiver, which must be kept cold. The condensed mercury is then dried and weighed. In the second case, the mercury is best precipitated by an alkaline formate. If the mercury be contained in the solution in any other form than the chloride, hydrochloric acid must be added, the solution nearly neutralised with potash, an alkaline formate added, and the whole digested for some days at a temperature not exceeding 80°: if the solution were boiled, the mercury would be reduced to the metallic state. The subchloride is collected on a weighed filter, dried at a gentle heat, and weighed. Mercury can only be estimated as sulphide in solutions from which hydrosulphuric acid precipitates the sulphide pure, (e. g. chloride of mercury): it is then sufficient to collect the sulphide on a filter, dry it in the water-bath, and weigh it. But if the sulphide be precipitated from a solution containing free nitric acid, or a sesquisalt of iron, it is mixed with sulphur, and cannot be weighed directly. In this case, the mercury must be separated from it in the metallic state, either in the wet or dry way, as above described.

In amalgams, the amount of mercury may be determined by the loss of weight produced by heat.

4. Bismuth. Bi. Atomic weight, 208.

Found native also in combination with oxygen, sulphur, tellurium, &c. It is a white metal with a reddish tinge: fuses at 260°. It is not affected by the air at the ordinary temperature: at a white heat it takes fire, forming bismuthic oxide, Bi2 ()3. Hydrochloric acid scarcely attacks it: nitric acid dissolves it readily sulphuric acid attacks it when hot and concentrated. Powdered bismuth burns in chlorine at the ordinary temperature, forming volatile chloride, BiC13.

OXIDES OF BISMUTH. Bismuthic Oxide, Bi203. Bismuthic Anhydride, Bi205.

a. Teroxide of Bismuth. Bismuthic oxide. Bi203.-A yellow powder, obtained by heating bismuth in the air, or by gently igniting the nitrate. It grows darker when heated: it may be fused to a glass, which is yellow and crystalline on cooling. It is not volatile. It is insoluble in water, soluble in all acids, forming bismuthic salts, which are colourless. They are partially decomposed by water, a basic salt being precipitated, and troubling the solution the addition of free acid dissolves the precipitate. This is the reaction chiefly employed for the detection of bismuth, The decomposition of the chloride by water is more complete than that of any other salt: hence it is well, in searching for small quantities of bismuth, to evaporate the solution to a small bulk with hydrochloric acid in a watch-glass, and add excess of The precipitate thus obtained is insoluble in tartaric acid. (Distinction of bismuth from antimony.) Hydrosulphuric acid and sulphide of ammonium give a black-brown precipitate of sulphide, Bi2S3, insoluble in alkaline sulphides, soluble in nitric acid. Sulphuric acid gives no precipitate. Chromate of potassium precipitates yellow chromate, soluble in nitric acid, insoluble in potash; by which it is distinguished from chromate of lead. Iodide of potassium precipitates brown iodide, Bil3, soluble in excess. Cyanide of potassium gives a white precipitate, insoluble in excess, soluble in acids. Ferrocyanide of potassium gives a white precipitate; ferricyanide of potassium, a pale yellow precipitate, both insoluble in hydrochloric acid. Alkaline carbonates

water.

precipitate a white basic carbonate, slightly soluble in excess, precipitated from the solution by potash. Ammonia and potash precipitate white hydrate, insoluble in excess: by boiling it is converted into the yellow oxide. Zinc, and several other metals, reduce metallic bismuth from its salts. All bismuth-salts, except the chloride, are decomposed when heated in the air.

b. Bismuthic Anhydride, Bi205.-A light-red powder, obtained by exposing the oxide, suspended in a strong solution of potash, to the action of chlorine. By ignition it is converted into the oxide. Heated with strong sulphuric or nitric acid it evolves oxygen, and forms a bismuth-salt. With hydrochloric acid in the cold it evolves chlorine, and forms chloride of bismuth. It is somewhat soluble in potash, and forms a few double salts of bismuth and potassium.

There are several oxides intermediate between bismuthic oxide and anhydride, which may be regarded as compounds of these two. They are all converted into the oxide by ignition, and evolve chlorine when treated with hydrochloric acid.

Blowpipe reactions.-All bismuth compounds, when heated on charcoal with carbonate of sodium in the inner flame, give a brittle metallic bead, and a yellow incrustation, which disappears when heated in the inner flame, without giving any colour to the outer flame (distinction of bismuth-oxide from lead-oxide). With borax and microcosmic salt bismuthic oxide gives beads which are yellowish when hot and colourless when cold. If much oxide be employed, the bead is opaque.

Separation and estimation of Bismuth.-The best qualitative test for bismuth is the decomposition of its chloride by water: the precipitate thus produced is insoluble in tartaric acid, potash, and sulphide of ammonium. From the metals of Subdivision A, bismuth is separated by the insolubility of its sulphide in sulphide of ammonium. From lead, by means of sulphuric acid in excess or by evaporation to dryness with hydrochloric acid and treating the residue with alcohol and ether, which dissolves the chloride of bismuth only. From silver, by hydrochloric acid. From mercury, by the solubility of its sulphide in nitric acid, or by the reduction of the mercury by chloride of tin.

K

Bismuth is always estimated as oxide. It is best precipitated by carbonate of ammonium, by which it is completely thrown down after some hours standing in a warm place. The precipitate is converted into oxide, Bi203, by ignition in a porcelain (not a platinum) crucible. Bismuth cannot be precipitated directly by carbonate of ammonium from a solution containing hydrochloric acid, for the precipitate would contain some oxychloride: in this case it must be precipitated as sulphide, the sulphide dissolved in nitric acid, and the solution precipitated by carbonate of ammonium.

5. Copper. Cu. Atomic weight, 31.7.

Found native: as suboxide (red copper-ore): as basic carbonate (malachite), sulphate, phosphate, &c.: as sulphide (copper-glance): as sulphide of copper and other metals (copper-pyrites, bournonite, fahl-ore, &c.). It has a red colour and a strong metallic lustre it is very ductile and tenacious, and difficultly fusible. It is not affected by dry air at the ordinary temperature: in moist air it becomes covered with a green coating of carbonate: in presence of acids it is rapidly oxidised by the air. When heated in the air it is converted into black oxide. Hydrochloric acid dissolves it but slightly, forming subchloride, Cu2Cl: nitric acid dissolves it readily: concentrated sulphuric acid dissolves it on heating, forming sulphate, SO4Cu2. Heated in chlorine it forms a mixture of chloride, CuCl, and subchloride.

OXIDES OF COPPER.

Suboxide, Cu4O. Oxide, Cu2O.

a. Suboxide of Copper. Cuprous Oxide. Cu1O.-A red powder, obtained by heating the oxide with metallic copper, or by boiling a protosalt of copper with grape-sugar, arsenious acid, &c., in presence of excess of potash. When heated in the air it is converted into oxide. All acids, except hydrochloric, decompose it into metallic copper, and cupric oxide, which dissolves in the acid, forming a protosalt. Hydrochloric acid dissolves it without decomposition, forming a solution of subchloride, Cu Cl, which is colourless when pure, but rapidly becomes brown, and then green, by absorption of oxygen and formation of chloride (p. 6). From the acid solution of subchloride, water precipitates white