cobalt containing free acid is scarcely or not at all precipitated; in absence of free acid, all or nearly all the cobalt is thrown down.

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 SULPHIide of COBALT (Co S). Chloride of ammonium greatly favors its separation. This substance is insoluble in alkalies and sulphide of ammonium, scarcely soluble in acetic acid, very difficultly 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 (cobalticyanide of potassium, K, Co, Cy1 = K3 Ckdy) is formed, in the solution of which acids produce no precipitate (important distinction from nickel).

6

9. Carbonate of baryta does not precipitate solutions of protoxide of cobalt in the cold, sulphate of cobalt excepted.

10. If nitrite of potassa is added in not too small proportion to a solution of protoxide of cobalt, then acetic acid to strongly acidreaction, 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 SESQUI

3

OXIDE OF COBALT AND POTASSA (Co2 O, 3 K O, 5 N O., 2 II O), in form of a crystalline precipitate of a beautiful yellow color. The mode in which this precipitate forms may be seen from the follow ing equation: 2 (Co O, S O) + 6 (K O, N O) + A = K O, A + 2 (K O, S O) + Co. O3, 3 K O, 5 N O + NO. 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 ast delicate as it is characteristic. Phosphate of soda and ammonia manifests with salts of cobalt before the blowpipe an analogous but less delicate reaction.

§ 113.

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, or in some cases, graphite remains.

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 hydrates are readily dissolved by hydrochloric, sulphuric, and nitric acids.

3. The SALTS OF PROTOXIDE OF IRON have in the anhydrous state a white, in the hydrated state a greenish color their solu

tions appear colored only when concentrated. Exposed to the air, they absorb oxygen and are converted into salts of the protosesquioxide with separation of basic sesquisalts. The soluble neutral salts redden litmus-paper, and are decomposed at a red heat.

4. Acid solutions of salts of protoxide of iron are not precipitated by hydrosulphuric acid; neutral solutions of salts of protoxide of iron with weak acids are precipitated by this reagent at the most but very incompletely; the precipitates are of a black color. 5. Sulphide of ammonium precipitates from neutral, and hydrosulphuric acid from alkaline solutions of salts of protoxide of iron, the whole of the metal as black hydrated PROTOSULPHIDE OF IRON (Fe S), which is insoluble in alkalies and sulphides of the alkali metals, but dissolves readily in hydrochloric and nitric acids: this black precipitate turns reddish-brown in the air by oxidation. To highly dilute solutions of protoxide of iron, addition of sulphide of ammonium imparts a green color, and it is only after some time that the protosulphide of iron separates as a black precipitate. Chloride of ammonium greatly facilitates the precipitation.

6. Potassa and ammonia produce a precipitate of HYDRATE OF PROTOXIDE OF IRON (Fe O, H O), which in the first moment looks almost white, but acquires after a very short time a dirty green, and ultimately a reddish-brown color, owing to absorption of oxygen from the air. Presence of salts of ammonia prevents the precipitation by potassa partly, and that by ammonia altogether.. If alkaline solutions of protoxide of iron thus obtained by the agency of salts of ammonia are exposed to the air, hydrates of protosesquioxide and of sesquioxide of iron precipitate.

7. Ferrocyanide of potassium produces in solutions of protoxideof iron a bluish-white precipitate of FERROCYANIDE OF POTASSIUM AND IRON (K, Fe, Cfy), which, by absorption of oxygen from the air, speedily acquires a blue color. Nitric acid or chlorine converts it immediately into Prussian blue, 3 (K, Fe, Cfy) + 4 Cl = 3 K Cl + Fe Cl + 2 (Fe, Cfy3).

8. Ferricyanide of potassium produces a magnificently blue precipitate of FERRICYANIDE OF IRON (Fe, Cfdy). This precipitate does not differ in color from Prussian blue. It is insoluble in hydrochloric acid, but is readily decomposed by potassa. In highly dilute solutions of salts of protoxide of iron the reagent produces simply a deep blue-green coloration.

9. Sulphocyanide of potassium does not alter solutions of prot oxide of iron free from sesquioxide.

10. Carbonate of Baryta does not precipitate solutions of protoxide of iron in the cold, solution of the sulphate excepted.

11. Borax dissolves salts of protoxide of iron in the oxidizing flame, giving beads varying in color from YELLOW to DARK-RED; when cold, the beads vary from colorless to dark-yellow. In the

inner flame the beads change to bottle-green, owing to the reduc tion of the newly-formed sesquioxide to protosesquioxide. Phosphate of soda and ammonia manifests a similar deportment with the salts of protoxide of iron; the beads produced with this reagent lose their color upon cooling still more completely than is the case with those produced with borax; the signs of the ensuing reduction in the reducing flame are also less marked.

§ 114.

f. SESQUIOXIDE OF IRON (Fe, O).

1. The native crystallized SESQUIOXIDE OF IRON is steel-gray; the native as well as the artificially prepared sesquioxide of iron gives upon trituration a brownish-red powder; the color of hydrate of sesquioxide of iron is more inclined to reddish-brown. Both the sesquioxide and its hydrate dissolve in hydrochloric, nitric, and sulphuric acids; the hydrate dissolves readily in these acids, but the anhydrous sesquioxide dissolves with greater difficulty, and completely only after long exposure to heat. The PROTOSES. QUIOXIDE (magnetic oxide Fe O, Fe, O3) is black, and dissolves in hydrochloric acid to a mixture of proto- and sesquichloride, in aqua regia to sesquichloride of iron.

2. The neutral anhydrous SALTS OF SESQUIOXIDE OF IRON are nearly white; the basic salts are yellow or reddish-brown. The color of the solutions is brownish-yellow, and becomes reddishyellow upon the application of heat. The soluble neutral salts redden litmus-paper, and are decomposed by heat.

3. Hydrosulphuric acid produces in acid solutions of salts of sesquioxide of iron containing the stronger acids, a milky white turbidity, proceeding from separated sulphur. At the same time the sesquisalt is converted into a protosalt. Fe2O3, 3 S O3 + HS = 2 (Fe O, S O) + HO, SO, + S. Solution of hydrosulphuric acid, rapidly added to neutral solutions, imparts to the fluid a transitory blackening. In solution of neutral acetate of sesquioxide of iron it precipitates the greater part of the iron. In presence of a sufficient quantity of free acetic acid only sulphur separates.

4. Sulphide of ammonium precipitates from neutral, and hydrosulphuric acid from alkaline solutions of salts of sesquioxide of iron, the whole of the metal as black hydrated PROTOSULPHIde of IRON (Fe S) mixed with sulphur. This precipitation is preceded by the reduction of the sesquioxide to protoxide. Fe, Cl, +3 N H, S = 3 N H, Cl + 2 Fe S + S. In very dilute solutions the reagent produces only a blackish-green coloration. The minutely divided protosulphide of iron subsides in such cases only after long standing. Its separation is greatly favored by presence of chloride of ammonium. Protosulphide of iron, as already stated (§113.5.), is

insoluble in alkalies and alkaline sulphides, but dissolves readily in hydrochloric and nitric acids.

5. Potassa and ammonia produce bulky reddish-brown precipitates of HYDRATE OF SESQUIOXIDE OF IRON (Fe, O, H O), which are insoluble in an excess of the precipitant as well as in salts of ammonia.

= 6

6. Ferrocyanide of potassium produces even in highly dilute solutions a magnificently blue precipitate of FERROCYANIDE OF IRON, or Prussian blue (Fe, Cfy) : 2 (Fe2 Cl) + 3 (Cfy. 2 K) K Cl+Fe, Cfy. This precipitate is insoluble in hydrochloric acid, but is decomposed by potassa, with separation of hydrate of sesquioxide of iron.,

7. Ferricyanide of potassium deepens the color of solutions of salts of sesquioxide of iron to reddish-brown; but it fails to produce a precipitate.

OF

8. Sulphocyanide of potassium imparts to neutral or slightly acid solutions of salts of sesquioxide of iron a most intense bloodred color, arising from the formation of a soluble SULPHOCYANIDE IRON.* Addition of acetate of sodat destroys this color, hydrochloric acid restores it again. This test is the most delicate of all; it will indicate the presence of sesquioxide of iron even in fluids which are so highly dilute that every other reagent fails to produce the slightest visible alteration. The red coloration may in such cases be detected most distinctly by resting the test-tube upon a sheet of white paper, and looking through it from the top.

[9. When a solution containing a sesquisalt of iron is rendered nearly neutral by carbonate of soda, and then heated to boiling with addition of excess of acetate of soda, all the iron is precipitated as brown BASIC SESQUIACETATE, and may be completely removed from the solution by filtering hot and washing with boiling water. If it is allowed to remain in the solution it partially redissolves as the latter becomes cold.]

10. Carbonate of baryta precipitates even in the cold all the iron as a basic salt mixed with hydrate of sesquioxide.

11. The reactions before the blowpipe are the same as with the protoxide.

§ 115.

Recapitulation and remarks.-On observing the behavior of the oxides of the fourth group with solution of soda, it would appear that the separation of the oxide of zinc, which is soluble in

[* A similar coloration is produced by sulphocyanide of potassium in solutions containing binoxide of molybdenum or hyponitric acid.]

So also phosphates, borates, fluorides, oxalates, tartrates, racemates, malates, citrates, succinates, and the corresponding acids]