8. Dilute sulphuric acid does not precipitate dilute solutions of nitrate of bismuth. If the solution containing excess of sulphurio acid be evaporated to dryness in the water-bath, there remains a white saline mass, which dissolves perfectly in water acidified with sulphuric acid (characteristic distinction from oxide of lead). From this solution, after long standing (perhaps for days), basic sulphate of bismuth (Bi O, S O3 + 2 aq.) crystallizes out in white microscopic needles which are soluble in nitric acid.

3

9. The reaction which especially characterizes the teroxide of bismuth, is the decomposition of its neutral salts by water with the formation of insoluble basic salts. The addition of a large amount of water to solutions of salts of bismuth, causes the immediate formation of a dazzling white precipitate, provided there be not too much free acid present. This reaction is the most sensitive with terchloride of bismuth, as the basic OXYCHLORIDE OF BISMUTH (Bi Cl, 2 Bi O3) is nearly insoluble in water. If water fails to produce a precipitate in nitric acid solutions of bismuth, owing to the presence of too much free acid, adding solution of chloride of sodium nearly always causes an immediate precipitation. From the basic salts of antimony which are formed under analogous circumstances, the precipitated basic salts of bismuth may be readily listinguished by their insolubility in tartaric acid.

10. If a mixture of a compound of bismuth with carbonate of soda is exposed on a charcoal support to the reducing flame of the blowpipe, brittle GLOBULES OF BISMUTHI are obtained, which fly into pieces under the stroke of a hammer. The charcoal becomes covered at the same time with a slight incrustation of TEROXIDE OF BISMUTH, which is orange when hot, and yellow when cold.

§ 125.

d. OXIDE OF CADMIUM (Cd O).

1. METALLIC CADMIUM has a tin-white color; it is lustrous, not very hard, malleable, ductile; it fuses at a temperature below red heat, and volatilizes at a temperature somewhat above the boiling point of mercury. It may therefore be easily sublimed in a glass tube. Heated on charcoal before the blowpipe, it takes fire and burns, emitting brown fumes of oxide of cadmium, which form a coating on the charcoal. Hydrochloric acid and dilute sulphuric acid dissolve it, with evolution of hydrogen; but nitric acid dissolves it nost readily.

2. OXIDE OF CADMIUM is a yellowish-brown, fixed powder; its hydrate is white. Both the oxide and its hydrate dissolve readily in hydrochloric, nitric, and sulphuric acids.

3. The SALTS OF OXIDE OF CADMIUM are colorless or white; some of them are soluble in water. The soluble salts, in the neutral state, redden litmus-paper, and are decomposed at a red heat.

4. Hydrosulphuric acid and sulphide of ammonium produce in alkaline, neutral, and acid solutions of salts of cadmium, bright yellow precipitates of SULPHIDE OF CADMIUM (Cd S), which are insoluble in dilute acids, alkalies, alkaline sulphides, and (distinction from copper) in cyanide of potassium. They are readily decomposed and dissolved by boiling nitric and hydrochloric acids, and (distinction from copper) in boiling dilute sulphuric acid. In solutions of salts of cadmium which contain a considerable excess of acid, hydrosulphuric acid produces a precipitate only after dilution with water.

5. Potassa produces in solutions of salts of cadmium a white precipitate of HYDRATE OF OXIDE OF CADMIUM (Cd O, H O), which is insoluble in an excess of the precipitant.

6. Ammonia likewise precipitates from solutions of salts of cadmium white HYDRATE OF OXIDE OF CADMIUM, which, however, redissolves readily to a colorless fluid in an excess of the precipitant.

7. Carbonate of potassa and carbonate of ammonia produce white precipitates of CARBONATE OF CADMIUM (Cd O, C O2), which are insoluble in an excess of the precipitants. The presence of salts of ammonia does not prevent the formation of these precipitates. The precipitated carbonate of cadmium dissolves readily in solution of cyanide of potassium. From dilute solutions the precipitate separates only after some time.

8. If a mixture of a compound of cadmium with carbonate of soda is exposed on a charcoal support to the reducing flame of the blowpipe, the charcoal becomes covered with a reddish-brown coating of OXIDE OF CADMIUM, owing to the volatilization of the reduced metal and its subsequent re-oxidation in passing through the oxidizing flame. The coating is seen most distinctly after cooling.

§ 126.

Recapitulation and remarks.-The perfect separation of the metallic oxides of the second division of the fifth group from suboxide of mercury and oxide of silver may, as already stated, be effected by means of hydrochloric acid; but this agent fails to separate them completely from oxide of lead. Traces of salts of oxide of mercury which may adhere to the chloride of silver are completely dissolved by washing.-(G. J. Mulder.) The oxide of mercury is distinguished from the other oxides of this division by the insolubility of the corresponding sulphide in boiling nitric acid. This property affords a convenient means for its separation. Care must be taken that the sulphides be completely freed from hydrochloric acid and metallic chlorides before treating them with nitric acid, as otherwise, mercury would go into solution. Moreover, the reactions with protochloride of tin or with metallic copper, as

well as those in the dry way, will, after the previous removal of the suboxide, always readily indicate the presence of oxide of mercury.

If the humid method be employed, it is best to dissolve the sulphide of mercury in hot hydrochloric acid with help of a fragment of chlorate of potassa.

From the still remaining oxides the oxide of lead is separated by addition of a sufficient quantity of dilute sulphuric acid; the separation is the most complete if the fluid, after the addition of sulphuric acid, is evaporated on the water-bath, the residue diluted with water containing some sulphuric acid and the insoluble sulphate of lead immediately filtered off. The latter can be examined in the dry way as described, § 120.10, or by heating a portion of it with solution of chromate of potassa. The white precipitate is thus converted into the yellow chromate of lead. It is washed and heated with soda-solution in which it dissolves. Addition of acetic acid to the alkaline solution throws down again yellow chromate of lead. After removal of the oxides of mercury and lead, teroxide of bismuth may be separated from oxide of copper and oxide of cadmium by addition of ammonia in excess, as the latter two oxides are soluble in an excess of this agent. If the filtered precipitate is dissolved in one or two drops of hydrochloric acid on a watchglass, and water added, the appearance of a milky turbidity is a confirmation of the presence of teroxide of bismuth. The presence of a notable quantity of oxide of copper is revealed by the blue color of the ammoniacal solution; smaller quantities are detected by evaporating the ammoniacal solution nearly to dryness, adding a little acetic acid, and then ferrocyanide of potassium. The separation of copper from cadmium may be effected by acting on the mixed sulphides of these metals by cyanide of potassium, or by boiling dilute sulphuric acid. The solution of the two metals is precipitated by hydrosulphuric acid and the sulphides are filtered off. If the sulphides be now covered with water and a fragment of cyanide of potassium added, the sulphide of copper dissolves, while yellow sulphide of cadmium remains behind. If the mixed sulphides be boiled with dilute sulphuric acid (1 part of strong acid to 6 parts of water) sulphide of cadmium is dissolved while sulphide of copper is unattacked. From the solution hydrosulphuric acid throws down yellow sulphide of cadmium.—(A. W. Hoffman.)

Special reactions of the rarer oxides of the fifth group.
§ 127.

1. PROTOXIDE OF PALLADIUM (Pd O).-Palladium greatly resembles platinum, with which it is usually associated in nature. Its color is, however, somewhat darker. It fuses with great difficulty; when heated in the air to dull redness, it becomes covered with a blue coating: but, upon more intense ignition, it recovers its light color and metallic lustre. It is difficultly soluble in pure nitric acid, but dissolve

somewhat more readily in nitric acid, containing nitrous acid; it dissolves very sparingly in boiling concentrated sulphuric acid, but readily in nitro-hydrochloric acid. It combines with 1 and 2 eq. of oxygen to form protoxide and binoxide. The latter in black, and when heated with dilute hydrochloric acid, evolves chlorine, and gives solution of protochloride of palladium. Protoxide of palladium is black, its hydrate dark brown; both are, upon intense ignition, resolved into oxygen and metallic palladium. The salts of protoxide of palladium are mostly soluble in water; they are brown, or reddish-brown; their solutions, when concentrated, are reddish brown; when dilute, yellow. Water precipitates from a solution of nitrate of protoxide of palladium containing a slight excess of acid, a brown-colored basic salt. The oxygen salts, as well as the protochloride, are decomposed upon ignition, leav. ing metallic palladium behind. Hydrosulphuric acid and sulphide of ammonium throw down from acid or neutral solutions of salts of protoxide of palladium, black protosulphide of palladium, which dissolves neither in sulphide of ammonium nor in boiling hydrochloric acid, and with difficulty in boiling nitric acid, but readily in nitro-hydrochloric acid. From the solution of the protochloride potassa precipitates a brown basic salt, soluble in an excess of the precipitant, ammonia, flesh colored ammonio protochloride of pulladium (Pd Cl, N H1), cyanide of mercury, yellowishwhite gelatinous protocyanide of palladium soluble in hydrochloric acid, and in ammonia (characteristic reaction). Protochloride of tin produces, in absence of free hydrochloric acid, a brownish-black precipitate; in presence of free hydrochloric acid, a red-colored solution, which speedily turns brown, and ultimately green, and, upon addition of water, brownish-red. Sulphate of protoxide of aron produces a deposit of palladium on the sides of the glass. Iodide of potassium precipitates black protiodide of palladium (characteristic reaction). Chloride of potassium precipitates from highly concentrated solutions of protoxide of palladium, potassio-protochloride of palladium (K Cl, Pd Cl), in form of golden-yellow needles, which dissolve readily in water, giving a dark red fluid, but are insoluble in absolute alcohol.

2. SESQUIOXIDE of Rhodium.-(R2 O3). Rhodium is found in small quantity in native platinum. It is a steel-gray, hard, brittle metal. In the state of powder it acquires oxygen at a red heat, and passes first into protoxide, afterwards into protosesquioxide. On stronger ignition it is reduced again to the metallic state. Rhodium is insoluble in all acids, even in nitro-hydrochloric. It dissolves in the latter when it is alloyed with platinum, copper, &c., but not when alloyed with gold and silver. It is dissolved as sesquioxide by fused hydrated phosphoric acid, as well as bisulphate of potassa. The sesquioxide is black, its hydrate greenish gray, or brown; it is insoluble in acids, but soluble in the fluxes above named. The solutions are rose red. Hydrosulphuric acid and sulphide of ammonium slowly precipitate, especially from warm solutions, brown sulphide of rhodium, which is insoluble in sulphide of ammonium but dissolves in boiling hydrochloric and nitric acids. Potassa precipitates brown hydrate only on boiling. If alcohol be added to the solution, made alkaline by potassa, rhodium is thrown down in the form of a black powder. The precipitation takes place only after the lapse of some time, when potassa is present in large excess.

Ammonia produces, after some time, a yellow precipitate which is soluble in hydrochloric acid Zine throws down black metallic rhodium. All the solid compounds of rhodium, when ignited in a stream of hydrogen, yield the metal, which is well characterized by its insolubility in nitrohydrochloric acid, its solubility in fusing bisulphate of potassa and the deportment of the solution towards potassa snd alcohol.

3. OXIDES OF OSMIUM.-Osmium accompanies native platinum as Iridosmine, &c. It is either a black powder or a gray brilliant mass, and is infusible. The metal, as well as its protoxide (0 0) and binoxide (Os O2), oxidize easily when heated in the air, to osmic acid (Os 0,) which is volatile and recognizable by its highly character.

istic, penetrating, and disagreeable odor, resembling that of chlorine and iodine. If ɔsnuum be placed on a strip of platinum foil, and brought into the outer mantel of the gas or alcohol flame at half its height, the flame becomes intensely luminous. In iridium containing minute traces of osmium, the latter may thus be detected; the reaction is, however, momentary; it may be reproduced by bringing the substance for a time into the reducing flame and then again into the outer mantel. Nitric acid, especially when red and fuming, and nitrohydrochloric acid, dissolve osmium to osmic acid. The solution is favored by heat, but with loss of osmic acid. Osmium which has been intensely ignited does not dissolve in acids. It should be fused with nitrate of potassa and the fused mass distilled with nitric acid; osmic acid passes into the distillate.

When osmium is heated in chlorine, there are formed green volatile protochloride of osmium (Os (1), and red, still more volatile bichloride (Os Cl2). The bichloride of osmium in solution rapidly decomposes, unless an alkaline chloride be present, into hydrochloric acid, osmic acid, and metallic osmium. All compounds of osmium yield, when heated in hydrogen gas, metallic osmium. Anhydrous osmic acid is white and crystalline, fusible at a gentle heat, boils at about 212° Fah., giving off vapors that attack the eyes and nostrils. Heated with water, it fuses and dissolves but slowly. The solution has a faint acid reaction and a strong disagreeable odor. Its solution is colored yellow, and its odor disappears on addition of alkalies. On heating with nitric or hydrochloric acid, the odor is again developed, and on distilling the mixture, osmic acid passes over (highly characteristic reaction). On evaporating solutions of alkaline osmates, especially if alkali be in excess, osmous acid (Os 0.) is formed. The reduction is aided by addition of alcohol. Hydrosulphuric arid produces brown sulphide of osmium (Os S,), which only separates in presence of a strong acid; it is insoluble in sulphide of ammonium. Sulphite of soda gives a deep blue-violet color, and osmium gradually separates as a black powder. Osmium is also thrown down as a black powder by protosulphate of iron and by formic acid, and in presence of a strong acid, by zinc and many other metals. The osmochiloride of potassium is difficultly soluble in cold, more easily in hot water; it is inso. luble in alcohol. On heating its solution with tannic acid it becomes of a deep blue color (characteristic}; formate of soda throws down from it black metallic osmium.

4. OXIDES OF RUTHENIUM-Ruthenium is found in small quantities in native platinum. It is a gray-white, brittle, very infusible metal, not attacked by fusing bisulphate of potassa, scarcely by aqua regia; ignited in the air, it is converted into bluish-black sesquioxide (Ru2 0.) which is insoluble in acids; ignited in a stream of chlorine gas with chloride of potassium, it gives ruthenochloride of potassium ; fused with hydrate, nitrate or chlorate of potassa it yields a greenish-black mass containing ruthenate of potassa (Ko Ru O3), which dissolves in water to an orangeyellow solution, that colors the skin black, from reduction and separation of black sesquioxide. From this solution, acids precipitate black oxide which is dissolved by hydrochloric acid, to an orange yellow liquid. The latter solution is decomposed by heating, into hydrochloric acid and brownish-black oxide of ruthenium; it gives when concentrated, crystalline, violet, shining precipitates with chlorides of ammonium and potassium, from which on boiling, black oxyprotochloride separates. Potassa throws down black hydrated oxide of ruthenium, which is insoluble in alkalies and soluble in acids. Hydrosulphuric acid at first, produces no change. After some time the solution becomes sky-blue, and brown sulphide of ruthenium separates (very characteristic reaction). Sulphide of ammonium gives a brown-black precipitate, which slightly dissolves in excess of the precipitant. Sulphocyanide of potassium produces (in absence of the other platinum metals), and after some time, a red coloration which gradually becomes purple, and on heating, violet (very characteristic reaction). Zine causes at first a sky-blue coloration, and afterwards a decoloration of the liquid with separation of metallic ruthenium.