a green precipitate is formed, consisting of a compound of sesquioxide of chromium with oxide of zinc (Zn O, Cr, O̟,). A solution of caustic soda or potassa therefore can never contain both oxides together in solution (Chancel).

7. Ammonia also produces in solutions of oxide of zinc, if they do not contain a large excess of free acid, a precipitate of HYDRATED OXIDE OF ZINC, which readily dissolves in an excess of the precipitant. The concentrated solution turns turbid when mixed with water. On boiling the concentrated solution, part of the oxide of zinc separates immediately; on boiling the dilute solution, all the oxide of zinc precipitates. 8. Carbonate of soda produces in solutions of salts of zinc a precipitate of BASIC CARBONATE OF ZINC (3 [Zn O, H O] + 2 [Zn O, C O2] + 4 aq.), which is insoluble in an excess of the precipitant. Presence of salts of ammonia in great excess prevents the formation of this precipitate.

9. Carbonate of ammonia also produces in solutions of salts of zinc the same precipitate of BASIC CARBONATE OF ZINC as carbonate of soda; but this precipitate redissolves upon further addition of the precipitant. On boiling the dilute solution, oxide of zinc precipitates.

10. Carbonate of baryta fails to precipitate solutions of oxide of zinc in the cold.

11. If a mixture of oxide of zinc, or one of its salts, with carbonate of soda is exposed to the reducing flame of the blowpipe, the charcoal support becomes covered with a slight coating of OXIDE OF ZINC, which presents a yellow color whilst hot, and turns white upon cooling. coating is produced by the reduced metallic zinc volatilizing at the moment of its reduction, and being reoxidized in passing through the outer flame.

This

12. If oxide of zinc or one of the salts of zinc is moistened with solution of nitrate of protoxide of cobalt, and then heated before the blowpipe, an unfused mass is obtained, of a beautiful GREEN color: this mass is a compound of oxide of zinc with protoxide of cobalt. If therefore in the experiment described in 11 the charcoal is moistened, around the little cavity, with solution of nitrate of protoxide of cobalt, the coating appears green when cold.

§ 106.

b. PROTOXIDE OF MANGANESE (Mn O).

1. Metallic manganese has a whitish-gray color and but little lustre ; it is brittle, and fuses with very great difficulty; it oxidizes slowly in cold water, rapidly in boiling water, and dissolves readily in acids. The solutions contain protoxide.

2. Protoxide of manganese is grayish-green; the hydrated protoxide is white. Both the protoxide and its hydrate absorb oxygen from the air, and are converted into the brown sesquioxide. They are readily soluble in hydrochloric, nitric, and sulphuric acids.

3. The salts of protoxide of manganese are colorless or pale red; part of them are soluble in water, the rest in acids. The salts soluble in water are readily decomposed by a red heat, with the exception of the sulphate. The solutions do not alter vegetable colors.

4. Hydrosulphuric acid does not precipitate acid solutions of salts of protoxide of manganese; neutral solutions also it fails to precipitate, or precipitates them only very imperfectly.

5. Sulphide of ammonium throws down from neutral, and hydrosulphuric acid from alkaline solutions of salts of protoxide of manganese, the whole of the metal as hydrated SULPHIDE OF MANGANESE (Mn S), in form of a light flesh-colored precipitate, which acquires a dark-brown color in the air; this precipitate is insoluble in yellow sulphide of ammonium and in alkalies, soluble to a very trifling extent in colorless sulphide of ammonium, but readily soluble in hydrochloric and nitric acids. From very dilute solutions the precipitate separates only after standing some time in a warm place.

6. Potassa, soda, and ammonia produce whitish precipitates of HYDRATE OF PROTOXIDE OF MANGANESE (Mn O, H O), which upon exposure to the air speedily acquire a brownish and finally a deep blackish-brown color, owing to the conversion of the hydrated protoxide into hydrated sesquioxide, by the absorption of oxygen from the air. Ammonia and carbonate of ammonia do not redissolve this precipitate; but presence of chloride of ammonium prevents the precipitation by ammonia altogether, and that by potassa partly. Of already formed precipitates solution of chloride of ammonium redissolves only those parts which have not yet undergone peroxidation. The solution of the hydrated protoxide of manganese in chloride of ammonium is owing to the disposition of the salts of protoxide of manganese to form double salts with salts of ammonia. The ammoniacal solutions of the double salts turn brown in the air, and deposit dark-brown hydrate of, sesquioxide of manganese (Otto).

7. If a few drops of a fluid containing protoxide of manganese, and free from chlorine, are sprinkled on binoxide of lead, or red-lead, nitric acid free from chlorine added, the mixture boiled and allowed to settle, the fluid is of a purple red color from the formation of permanganic acid.

8. Carbonate of baryta does not precipitate protoxide of manganese from its solutions, upon digestion in the cold.

9. If any compound of manganese, in a state of minute division, is fused with carbonate of soda on a platinum wire in the outer flame of the blowpipe, MANGANATE OF SODA (Na O, Mn 01) is formed, which makes the fused mass appear GREEN while hot, and of a BLUISH-GREEN tint after cooling, the bead at the same time becoming turbid. reaction enables us to detect the smallest quantities of manganese. delicacy of the test may be still further increased by the addition of a minute quantity of nitrate of potassa to the carbonate of soda.

This

The

10. Borax and phosphate of soda and ammonia dissolve manganese compounds in the outer flame of the blowpipe to clear VIOLET-RED beads, which upon cooling acquire an AMETHYST-RED tint: they lose their color in the inner flame, owing to a reduction of the sesquioxide to protoxide. The bead which borax forms with manganese compounds appears black when containing a considerable portion of sesquioxide of manganese, but that formed by phosphate of soda and ammonia never loses its transparency. But the latter loses its color in the inner flame of the blowpipe far more readily than the former.

§ 107.

C. PROTOXIDE OF NICKEL (Ni O).

1. Metallic nickel in the fused state is silvery white, inclining to gray; * If the quantity of the precipitate is only trifling, the color appears yellowish-white.

it is bright, hard, malleable, ductile, difficultly fusible; it does not oxidize in the air at common temperatures, but it oxidizes slowly upon ignition; it is attracted by the magnet, and may itself become magnetic. It slowly dissolves in hydrochloric acid and dilute sulphuric acid upon the application of heat, the solution being attended with evolution of hydrogen gas. It dissolves readily in nitric acid.

2. Protoxide of nickel is a gray, its hydrate a green powder. Both the protoxide and its hydrate are unalterable in the air, and readily soluble in hydrochloric, nitric, and sulphuric acids.

3. Most of the salts of protoxide of nickel are yellow in the anhydrous, green in the hydrated state; their solutions are of a light green color. The soluble neutral salts slightly redden litmus paper, and are decomposed at a red heat.

4. Hydrosulphuric acid does not precipitate acid solutions of salts of nickel ; it fails also to precipitate neutral solutions of salts of nickel with the stronger acids, or it precipitates them only very imperfectly.

5. Sulphide of ammonium produces in neutral, and hydrosulphuric acid in alkaline solutions of salts of protoxide of nickel, a black precipitate of hydrated SULPHIDE OF NICKEL (Ni S), which is not altogether insoluble in sulphide of ammonium, especially if containing free ammonia; the fluid from which the precipitate has been thrown down exhibits therefore usually a brownish color. Sulphide of nickel dissolves with great difficulty in hydrochloric acid, but readily in nitrohydrochloric acid upon application of heat.

6. Potassa and soda produce a light green precipitate of HYDRATE OF PROTOXIDE OF NICKEL (Ni O, H O), which is insoluble in an excess of the precipitants, and unalterable in the air. Carbonate of ammonia dissolves this precipitate, when filtered and washed, to a greenish-blue fluid, from which potassa or soda reprecipitates the nickel as an apple-green hydrate of protoxide of nickel.

7. Ammonia added in small quantity to solutions of protoxide of nickel produces in them a trifling greenish turbidity; upon further addition of the reagent this redissolves readily to a blue fluid containing a compound of protoxide of nickel and ammonia. Potassa and soda precipitate from this solution hydrate of protoxide of nickel. Solutions containing salts of ammonia or free acid are not rendered turbid by ammonia.

8. Cyanide of potassium produces a yellowish-green precipitate of CYANIDE OF NICKEL (Ni Cy), which redissolves readily in an excess of the precipitant as a double cyanide of nickel and potassium (Ni Cy+ K Cy); the solution is brownish-yellow. If sulphuric acid or hydrochloric acid is added to this solution, the cyanide of potassium is decomposed, and the cyanide of nickel reprecipitated; the latter substance is very difficultly soluble in an excess of these acids in the cold, but more readily upon boiling.

9. Carbonate of baryta does not precipitate protoxide of nickel from its solutions, upon digestion in the cold.

10. Nitrite of potassa, used in conjunction with acetic acid, fails to precipitate even concentrated solutions of nickel.

11. Borax and phosphate of soda and ammonia dissolve compounds of protoxide of nickel in the outer flame of the blowpipe to clear beads; the bead produced with borax is violet whilst hot, reddish-brown when cold; the bead produced with the phosphate of soda and ammonia is reddish, inclining to brown whilst hot, but turns yellow or reddish-yellow upon cool

ing. The bead which phosphate of soda and ammonia forms with salts of protoxide of nickel remains unaltered in the inner flame of the blowpipe, but that formed with borax turns gray and turbid from reduced metallic nickel. Upon continued exposure to the blowpipe flame the particles of nickel unite, but without fusing to a grain, and the bead becomes colorless. § 108.

d. PROTOXIDE OF COBALT (Co O).

1. Metallic cobalt is reddish-gray, slightly lustrous, pretty hard, slightly malleable, ductile, and difficultly fusible; it does not oxidize in the air at the common temperature, and oxidizes only slowly at a red heat; with acids it comports itself like nickel.

2. Protoxide of cobalt is an olive-green, its hydrate a pale red powder. Both dissolve readily in hydrochloric, nitric, and sulphuric acids.

3. The salts of protoxide of cobalt, containing water of crystallization, are red, the anhydrous salts mostly blue. The moderately concentrated solutions appear of a light red color, which they retain even though considerably diluted. The soluble neutral salts redden litmus paper slightly, and are decomposed at a red heat; sulphate of protoxide of cobalt alone can bear a moderate red heat without suffering decomposition. When a solution of chloride of cobalt is evaporated, the light red color changes towards the end of the operation to blue; addition of water restores the red color.

4. Hydrosulphuric acid does not precipitate acid solutions of cobalt ; it also fails to precipitate neutral solutions of salts of protoxide of cobalt with the stronger acids, or it precipitates them only very imperfectly.

5. Sulphide of ammonium precipitates from neutral, and hydrosulphuric acid from alkaline solutions of salts of protoxide of cobalt, the whole of the metal as black hydrated SULPHIDE OF COBALT (Co S). This substance is insoluble in alkalies and sulphide of ammonium, very difficultly soluble in hydrochloric acid, but readily so in nitrohydrochloric acid upon application of heat.

6. Potassa and soda produce in solutions of cobalt BLUE precipitates of basic salts of cobalt, which turn GREEN upon exposure to the air, owing to the absorption of oxygen; upon boiling, they are converted into pale red hydrate of protoxide of cobalt, which contains alkali, and generally appears rather discolored from an admixture of sesquioxide formed in the process. These precipitates are insoluble in solutions of potassa and soda; but neutral carbonate of ammonia dissolves them completely to intensely violet-red fluids, in which a somewhat larger proportion of potassa or soda produces a blue precipitate, the fluid still retaining its violet color.

7. Ammonia produces the same precipitate as potassa, but this redissolves in an excess of the ammonia to a reddish-brown fluid, from which solution of potassa or soda throws down part of the cobalt as a blue basic salt. Ammonia fails to precipitate solutions of protoxide of cobalt containing salts of ammonia or free acid.

8. Addition of cyanide of potassium to a solution of cobalt gives rise to the formation of a brownish-white precipitate of PROTOCYANIDE OF COBALT (Co Cy), which dissolves readily as a double cyanide of cobalt and potassium in an excess of solution of cyanide of potassium. Acids precipitate from this solution cyanide of cobalt. But if the solution is

boiled with cyanide of potassium in excess, in presence of free hydrocyanic acid (liberated by addition of one or two drops of hydrochloric acid), a double compound of sesquicyanide of cobalt and cyanide of potassium (K,, Co, Cy1 = K, Ckdy) is formed, in the solution of which acids produce no precipitate.

9. Carbonate of baryta does not precipitate solution of protoxide of cobalt in the cold.

10. If nitrite of potasse is added in not too small proportion to a solution of protoxide of cobalt, then acetic acid to strongly acid reaction, and the mixture put in a moderately warm place, all the cobalt separates, from concentrated solutions immediately or very soon, from dilute solutions after some time, as NITRITE OF SESQUIOXIDE OF COBALT AND POTASSA (Co, O, 3 K 0, 5 N O,, 2 H O), in form of a crystalline precipitate of a beautiful yellow color. The mode in which this precipitate forms may be seen from the following equation: 2 (Co O, SO) + 6 (KO, NO1) + A = K 0, A + 2 KO, SO, + Co, O,, 3 K 0, 5 NO, + NO2. The precipitate is only sparingly soluble in pure water, and altogether insoluble in saline solutions and in alcohol. When boiled with water, it dissolves, though not copiously, to a red fluid, which remains clear upon cooling, and from which alkalies throw down hydrate of protoxide of cobalt (Fischer, Aug. Stromeyer). This excellent reaction enables us to distinguish nickel from cobalt. It is always necessary to concentrate the solution of protoxide of cobalt to a considerable extent before adding the nitrite of potassa.

11. Borax dissolves compounds of cobalt both in the inner and outer flame of the blowpipe, giving clear beads of a magnificent BLUE color, which appear violet by candle-light, and almost black if the cobalt is present in considerable proportion. This test is as delicate as it is characteristic. Phosphate of soda and ammonia manifests with salts of cobalt before the blowpipe an analogous but less delicate reaction.

§ 109.

e. PROTOXIDE OF IRON (Fe O).

1. Metallic iron in the pure state has a light whitish gray color (iron containing carbon is more or less gray); the metal is hard, lustrous, malleable, ductile, exceedingly difficult to fuse, and is attracted by the magnet. In contact with air and moisture a coating of rust (hydrate of sesquioxide of iron) forms on its surface; upon ignition in the air, a coating of black protosesquioxide. Hydrochloric acid and dilute sulphuric acid dissolve iron, with evolution of hydrogen gas; if the iron contains carbon, the hydrogen is mixed with carbide of hydrogen. The solutions contain protoxide. Dilute nitric acid dissolves iron in the cold to nitrate of protoxide, with evolution of nitrous oxide; at a high temperature, to nitrate of sesquioxide, with evolution of nitric oxide; if the iron contains carbon, some carbonic acid is also evolved, and there is left undissolved a brown substance resembling humus, which is soluble in alkalies.

2. Protoxide of iron is a black powder; its hydrate is a white powder, which in the moist state absorbs oxygen and speedily acquires a grayish-green, and ultimately a brownish-red color. Both the protoxide and its hydrate are readily dissolved by hydrochloric, sulphuric, and nitric acids.