on a platinum wire to the inner blowpipe flame, color the outer flame INTENSELY YELLOW. This reaction remains clearly perceptible, even if the soda contains a considerable admixture of potassa. Chloride of silver promotes the reaction in the case of some, but not of all salts of soda.

4. If a salt of soda (more particularly chloride of sodium) is heated with a small quantity of water, alcohol added, and the latter heated and then kindled, the flame appears strongly YELLOW. The presence of a salt of potassa does not impair the distinctness of this reaction.

5. Bichloride of platinum produces no precipitate in solutions of salts of soda; tartaric acid only when a highly concentrated solution of soda or carbonate of soda is mixed with a saturated solution of tartaric

acid in excess. The bulky precipitate of BITARTRATE OF SODA which in that case separates, consists of small needles and columns, and requires only 12 parts of cold water for its solution; it is not likely, therefore, to be confounded with the granular crystalline precipitate of bitartrate of potassa.

$ 90.

C. AMMONIA (N H, O).

1. Anhydrous ammonia (N H) is gaseous at the common temperature; but we have most frequently to deal with it in its aqueous solution, in which it betrays its presence at once by its penetrating odor. It is expelled from this solution by the application of heat. It may be assumed that the solution contains it as oxide of ammonium (N H, O) (see § 31).

2. All the salts of ammonia are volatile at a high temperature, either with or without decomposition. Most of them are readily soluble in water. The solutions are colorless. The neutral compounds of ammonia with strong acids do not alter vegetable colors.

3. If salts of ammonia are triturated together with hydrate of lime, best with the addition of a few drops of water, or are, either in a solid form or in solution, heated with solution of potassa or of soda, the ammonia is liberated in the gaseous state, and betrays itself (1) by its characteristic odor; (2) by its reaction on moistened test-papers; and (3) by giving rise to the formation of white fumes, when any object (e. g., a glass rod) moistened with hydrochloric acid, nitric acid, acetic acid, or any of the volatile acids, is brought in contact with it. These fumes arise from the formation of solid ammoniacal salts produced by the contact of the gases in the air. Hydrochloric acid is the most delicate test in this respect; acetic acid, however, admits less readily of a mistake. In cases where the quantity of ammonia present is only very small, the best way of testing the alkaline reaction of the fumes is to cover a small beaker containing the mixture with a watch-glass, having a slip of moistened turmeric or reddened litmus-paper attached to the convex side, to place it on a hot slab, and observe, after a few minutes, whether the test-paper has changed color.

4. Bichloride of platinum shows the same deportment with salts of ammonia as with salts of potassa; the yellow precipitate of BICHLORIDE OF PLATINUM AND CHLORIDE OF AMMONIUM (N H, Cl, Pt Cl2) is, however, of a somewhat lighter color than potassio-bichloride of platinum. It consists, like the corresponding potassium compound, of octahedrons, discernible under the microscope.

5. Tartaric acid added in excess to a solution of ammonia or carbonate

4

of ammonia, produces a white crystalline precipitate of BITARTRATE OF AMMONIA (N H, HO, C, H, O). In concentrated solutions this precipitate forms immediately; in dilute solutions only after some time. The solutions of other ammoniacal salts (chloride of ammonium, nitrate of ammonia, &c.) are not precipitated by this reagent, even when highly concentrated; or a trifling precipitate only separates after long standing. Bitartrate of ammonia comports itself with solvents like the corresponding salt of potassa; however, it is somewhat more readily soluble in water and acids than the latter.

6. If a solution of potassio-iodide of mercury,* containing much caustic potassa, is mixed with a fluid containing ammonia or an ammoniacal salt, a reddish-brown precipitate of hydrated TETRAHYDRARGYROIODIDE OF AMMONIUM (N Hg,I + 2 H O) : 4 (Hg I, K I) + 3 K O + N H ̧ (N Hg, I + 2 HO) +7 KI+HO, separates immediately or upon application of a gentle heat. This precipitate redissolves in presence of an excess of ammoniacal salts; but reprecipitates upon further addition of potassa; it is soluble also in solution of iodide of potassium, but the less so the more free potassa happens to be present. When a considerable excess of potassa exists, therefore, the precipitate is insoluble in iodide of potassium. Presence of chlorides of the alkali metals, or of salts of potassa and soda, does not interfere with the reaction; but cyanides and sulphides of the alkali metals prevent it. This reaction was first pointed out by Nessler; it is not required for ordinary analyses, but is extremely valuable in cases where the presence of minute traces of ammoniacal salts are to be detected. I have found it to give distinct indications of the presence of ammonia in solutions of 0·00001 gramme of chloride of ammonium in 1 cubic centimètre of water.

§ 91.

Recapitulation and remarks.—The salts of potassa and soda are not volatile at a moderate red heat, whilst the salts of ammonia volatilize readily; the latter may therefore be easily separated from the former by ignition. The expulsion of ammonia from its compounds, by hydrate of lime, affords the surest means of ascertaining the presence of this substance. Salts of potassa can be detected positively only after the removal of the ammoniacal salts which may be present, since both classes of salts manifest the same or a similar deportment with bichloride of platinum and tartaric acid. After the removal of the ammonia, the potassa is clearly and positively characterized by either of these two reagents. The most simple way of detecting the potassa in the two difficulty-soluble compounds that have come under our consideration here-viz., the potassio-bichloride of platinum and bitartrate of potassa-is to decompose these salts by ignition; the former, thereupon, yields the potassa in the form of chloride of potassium, the latter in the form of carbonate of potassa. With respect to soda, the yellow tint which its salts Impart to the blowpipe flame and to the flame of alcohol, is a safe and mostly in itself sufficient proof of its presence, provided always no other bodies be present besides salts of fixed alkalies. In form of chlorides, Toth part of soda may by this means be detected in presence of potassa. Anti

To prepare this reagent, digest at a gentle heat 2 grammes of iodide of potassium, and 3 grammes of iodide of mercury, in 5 cub. cent. of water; add 20 cub. cent. of water, let the mixture stand for some time, then filter; add to the filtrate 30 cub. cent. of pure concentrated solution of potassa (1: 4); and, should a precipitate form, let this settle; decant, and use the clear decanted fluid.

monate of potassa also gives decisive results when no other bases besides soda or potassa are present, and especially if these latter are present as chlorides or nitrates. Even from very dilute solutions of salts of soda, antimonate of potassa added in excess will, after twelve hours' standing, throw down antimonate of soda, the crystals of which may always be readily and distinctly recognised under the microscope by their form-quadrilateral octahedrons.

$ 92.

SUPPLEMENT TO THE FIRST GROUP.

LITHIA (LI O).

5

Lithia dissolves with difficulty in water; it does not attract moisture from the air. Most of its salts are soluble in water; some of them are deliquescent (chloride of lithium). Carbonate of lithia is difficultly soluble, particularly in cold water. Phosphate of soda produces, in not over dilute solutions of salts of lithia, upon boiling, a heavy white crystalline precipitate of basic phosphate of lithia (3 Li O, PO,+ aq.). From very dilute solutions of lithia the same basic phosphate is obtained by adding phosphate of soda and one or two drops of solution of soda to the solution, evaporating the mixed fluid to dryness, and treating the residue with water. The basic phosphate of lithia obtained is sparingly soluble in water, and still less so in ammoniated water; it dissolves much more readily in water containing salts of ammonium. It is immediately dissolved by acids; addition of ammonia produces no precipitate in somewhat dilute acid solutions in the cold, but upon boiling, a precipitate separates. The basic phosphate of lithia fuses before the blowpipe, and gives upon fusion with carbonate of soda on the platinum wire a clear bead; when fused upon charcoal, it is absorbed by the pores of the latter body (another difference between it and the phosphate of the alkaline earths). Tartaric acid and bichloride of platinum fail to precipitate even concentrated solutions of salts of lithia; but in a solution of chloride of potassium containing chloride of lithium, bichloride of platinum readily produces a precipitate containing lithia (Jenzsch). If a salt of lithia (more particularly chloride of lithium) is exposed on a platinum wire to the inner blowpipe flame, the outer flame shows a strong CARMINE tint. Presence of salts of soda (but not of salts of potassa) conceals this reaction. Addition of chloride of silver promotes it in the case of some, but not of all salts of lithia. If spirit of wine is poured over a salt of lithia (more particularly chloride of lithium), and then kindled, the flame appears of a CARMINE colour; presence of salts of soda conceals this reaction.

To detect lithia in presence of potassa and soda, convert the bases into dry chlorides; treat them, after addition of a drop of hydrochloric acid, with a mixture of absolute alcohol and anhydrous ether; filter, distil, and treat the residue remaining after distillation again with the said mixture, after previous addition of a drop of hydrochloric acid; filter, concentrate the filtrate by evaporation, and then set fire to the concentrated fluid. A carmine-coloured flame indicates the presence of lithia. The residue remaining after evaporation of the alcohol must dissolve in water to a clear fluid; the solution must not be precipitated by carbonate of ammonia (lime, strontia), and must give the above-mentioned reaction with phosphate of soda. This method is based upon the insolubility of chloride

of potassium, and chloride of sodium in absolute alcohol and ether, in which chloride of lithium readily dissolves.

§ 93.

SECOND GROUP.

BARYTA, STRONTIA, LIME, MAGNESIA.

Properties of the group.-The alkaline earths are soluble in water in the pure (caustic) state and as sulphides. Magnesia, however, dissolves but very sparingly in water. The solutions manifest alkaline reaction; the alkaline reaction of magnesia is most clearly apparent when that earth is laid upon moistened test-paper. The neutral carbonates and The solutions phosphates of the alkaline earths are insoluble in water.

of the salts of the alkaline earths are therefore precipitated by alkaline carbonates and phosphates, whilst hydrosulphuric acid fails to precipitate them under any condition. This deportment distinguishes the oxides of the second group from those of the first. The alkaline earths and their salts are non-volatile and colorless; their solutions are not precipitated by sulphide of ammonium, nor by carbonate of baryta.

Special Reactions.
$94.

a. BARYTA (Ba O).

1. Caustic baryta is pretty readily soluble in hot water, but rather difficultly so in cold water; it dissolves easily in dilute hydrochloric or nitric acid. Hydrate of baryta does not lose its water upon ignition. The soluble 2. Most of the salts of baryta are insoluble in water. salts do not affect vegetable colors, and are decomposed upon ignition, The insoluble salts dissolve with the exception of chloride of barium. in dilute hydrochloric acid, except the sulphate of baryta. Nitrate of baryta and chloride of barium are insoluble in alcohol, and do not deliquesce in the air. Concentrated solutions of baryta are precipitated by hydrochloric or nitric acid added in large proportions, as chloride of barium and nitrate of baryta are not soluble in the aqueous solutions of

the said acids.

3. Ammonia (free from carbonic acid) produces no precipitate in the aqueous solutions of salts of baryta; potassa or soda (free from carbonic Water redissolves the acid) only in highly concentrated solutions. bulky precipitate of CRYSTALS OF BARYTA (Ba O, HO + 8 aq.) produced by potassa or soda.

4. Alkaline carbonates throw down from solutions of baryta CARBONATE OF BARYTA (Ba O, C O2) in the form of a white precipitate. When carbonate of ammonia is used as the precipitant, or if the solution was previously acid, complete precipitation takes place only upon heating the fluid. In chloride of ammonium the precipitate is soluble to a trifling yet clearly perceptible extent; in very dilute solutions of baryta, therefore, which contain much chloride of ammonium, carbonate of ammonia produces no precipitate.

5. Sulphuric acid and all the soluble sulphates, also solution of sulphate of lime, produce even in very dilute solutions of baryta, a

heavy, finely pulverulent, white precipitate of SULPHATE OF BARYTA (Ba O, S 0), which is insoluble or very difficultly soluble in dilute acids, alkalies, and salts of ammonia. As a rule, this precipitate is formed immediately upon the addition of the reagent; from highly dilute solutions, however, especially when strongly acid, it separates only after some time. Sulphate of baryta is completely decomposed by fusion with carbonates of the alkalies-less readily and less completely by boiling with solution of carbonate of soda and carbonate of potassa. The decomposition leads to the formation of sulphates of the alkalies, which are soluble in water, and carbonate of baryta, which is insoluble in that fluid. Digestion with solution of carbonate of ammonia in the cold fails to effect the decomposition of sulphate of baryta, as also boiling with a solution of 1 part of carbonate and 3 parts of sulphate of potassa (H. Rose).

6. Hydrofluosilicic acid throws down from solutions of baryta SILICOFLUORIDE OF BARIUM (Ba Fl + Si Fl), in form of a colorless, crystalline, quickly subsiding precipitate. In dilute solutions this precipitate is formed only after the lapse of some time; it is perceptibly soluble in hydrochloric and nitric acids. Addition of an equal volume of alcohol hastens the precipitation and makes it so complete that the filtrate remains clear upon addition of sulphuric acid.

7. Phosphate of soda produces in neutral or alkaline solutions of baryta a white precipitate of PHOSPHATE OF BARYTA (2 Ba O, H O, P 0), which is soluble in free acids. Addition of ammonia only slightly increases the quantity of this precipitate; chloride of ammonium dissolves it to a clearly perceptible extent.

8. Oxalate of ammonia produces in moderately dilute solutions of baryta a white, pulverulent precipitate of oXALATE OF BARYTA (Ba O, Ō + aq.), which is soluble in hydrochloric and nitric acids. When recently thrown down, this precipitate dissolves also in oxalic and acetic acids; but the solutions speedily deposit binoxalate of baryta (Ba 0,0 + H 0,0 + 2 aq.) in the form of a crystalline powder.

9. Salts of baryta in powder, when heated with dilute spirit of wine, impart to the flame a YELLOWISH colour, which, however, is not very characteristic.

10. Salts of baryta, particularly chloride of barium, when exposed on a platinum wire to the inner blowpipe flame, color the outer flame YELLOWISH-GREEN. With chloride of barium and nitrate and acetate of baryta this reaction is the most distinct, but it is also shown by carbonate and sulphate of baryta. The presence of salts of lime and strontia does not prevent the reaction; addition of chloride of silver considerably heightens its intensity.

$ 95.

b. STRONTIA (Sr O).

1. Strontia and its hydrate and salts manifest nearly the same general deportment and properties as baryta and its corresponding compounds.Hydrate of strontia is more difficulty soluble in water than hydrate of baryta. Chloride of strontium dissolves in absolute alcohol, and deliquesces in moist air. Nitrate of strontia is insoluble in absolute alcohol, and does not deliquesce in the air.

2. The salts of strontia manifest with ammonia and potassa, and also