In the spectroscope the characteristic lines of both alkalies appear at once with such distinctness as to preclude all chances of mistake. [Potassa is masked by much soda.]

[For detecting soda in presence of potassa, antimonate of potassa is somewhat troublesome to prepare and apply. The spectral and flame tests do not always enable the operator to discriminate between accidental traces of soda and such quantities as constitute it an essential or weighable ingredient, of a compound or mixture. A method that supplies this deficiency, is moreover easy of application to very small quantities of substance, and that serves for the simultaneous detection of both alkalies, is the following, described by J. Lawrence Smith. The alkali metals must exist as chlorides, and must be free from organic acids or other bases. A small fragment of the solid substance, which need not exceed of an inch in diameter, or a drop of its concentrated aqueous solution, is placed on a slip of glass, and to it is added a single drop of aqueous solution of bichloride of platinum. The plate is now gently warmed; if potassa be present a yellow deposit soon forms, which, under a good magnifier, is seen to consist of octahedral crystals of platinchloride of potassium; the warming is continued until the liquid begins to dry on the edges; if it now be examined with the mag nifier the characteristic slender yellow prisms of platinchloride of sodium will be seen. If potassa be present in such quantity that a copious precipitate of platinchloride of potassium separates on addition of bichloride of platinum, it is best to add another drop of the reagent, and allow the precipitate to subside. The liquid is poured off upon another slip of glass, and warmed as abovedescribed. When larger quantities of materials are employed, the unassisted eye may usually recognize the crystals of platinchloride of sodium. In looking for minute quantities of soda, recourse must be had to the compound microscope. If the slip of glass be viewed in the microscope by polarized light, the reaction becomes extremely sensitive, as the crystals of platinchloride of sodium assume prismatic colors, while those of the potassium salt do not transmit polarized light.

If the beginner fails to find prismatic crystals the first time he evaporates the mixture on the glass slip, he should add a drop of water and repeat the evaporation more slowly. This reaction for soda is uncertain in presence of lithia.]

For the detection of exceedingly minute traces of ammonia a reaction first pointed out by Nessler may be employed. 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, filter again. If to this solution is added, in small quantity, a liquid containing ammonia or an ammonia-salt, a reddish brown precipitate, or with

VIMU

a little time-phosphate of baryta and silicates decomposable by acids, after moistening with sulphuric or hydrochloric acid. Silicates not decomposable by acids must be fluxed with carbonate of soda, and the carbonate of baryta thus obtained is examined in the flame. The presence of salts of lime and strontia does not prevent the reaction when the sulphates are employed.

11. The baryta flame is characterized by its appearing blue green when viewed through the green glass.

12. The spectrum of baryta is figured on Plate I. The green lines a and B are the most intense. Less distinct but still characteristic is the line 7.

13. SULPHATE OF BARYTA is not all or but very slightly decomposed by cold solutions of alkaline bicarbonates or of carbonate of ammonia. It is also not perceptibly decomposed by a boiling solution of 1 part of carbonate and 3 parts of sulphate of potassa. Boiling solutions of neutral carbonates of the alkalies, if renewed sufficiently often, decompose it completely. By fusing it with carbonate of soda or potassa, it is easily and perfectly decomposed, there being formed sulphate of the alkali which is soluble, and carbonate of baryta which is insoluble in water.

§ 99.

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 difficultly 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 with the alkaline carbonates and with phosphate of soda, nearly the same deportment as the salts of baryta. Carbonate of strontia dissolves somewhat more difficultly in chloride of ammonium than is the case with carbonate of baryta.

3. Sulphuric acid and sulphates precipitate from solutions of strontia SULPHATE OF STRONTIA (Sr O, S O), in form of a white powder. Application of heat greatly promotes the precipitation. Sulphate of strontia is far more soluble in water than sulphate of baryta; owing to this readier solubility, the precipitated sulphate of strontia separates from rather dilute solutions, in general, only after the lapse of some time; and this is invariably the case (even in concentrated solutions) if solution of sulphate of lime is used as precipitant. Sulphate of strontia is insoluble in alcohol; addition of the latter, therefore, facilitates its separation. It is perceptibly

Lithia forms the transition from the first to the second group. It is soluble in water with difficulty, and does not become moist by exposure to the air. Its salts are mostly soluble in water, and some of them (chloride of lithium) are deliquescent. Carbonate of lithia is difficultly soluble, especially in cold water.

Phosphate of sodu produces in not too dilute solutions of lithia salts, on boiling, a white crystalline quickly subsiding precipitate of tribasic phosphate of lithia. (3 Li O PO). This characteristic reaction is far more sensitive when the solution of the lithia salt together with phosphate of soda, and so much soda-lye as suffices to maintain an alkaline reaction is evaporated to dryness, the residue softened with water, and an equal volume of solution of ammonia added. In this way very small quantities of lithia may be separated as phosphate. This precipitate fuses before the blowpipe, with carbonate of soda melts to a clear bead; fused on charcoal, it is absorbed by the latter. It dissolves in hydrochloric acid to a solution which remains clear after addition of ammonia in excess; but, on boiling. separates again with its original characters-(Distinction from the alkaline earths). Tartaric acid and bichloride of platinum do not affect even concentrated solutions of lithia-salts. When a salt of lithia is brought into the blowpipe or gas-flame (§ 14.) the latter is tinged carminered. Silicates containing lithia are mixed with sulphate of lime. Phosphate of lithia colors the flame when the fused salt is moistened with hydrochloric acid. The lithia flame is completely masked by that of soda, and when the latter substance is present the flame must be examined by a blue glass or by the thinner parts of the indigo prism. A small quantity of potassa does not disguise the lithia flame. In presence of much potassa, lithia may be detected by comparing through the indigoprism the flame of the substance to be tested with that of a pure potassa-salt. In this experiment, the two substances are placed near each other on opposite sides of the zone of fusion of the Bunsen lamp. The potassa-lithia flame, viewed through the narrow part of the prism, appears redder in color than the pure potassa flame; at a certain thicker point in the prism both flames appear equally red if the proportion of lithia is very small. If lithia predominates, the intensity of the flame reddened by it, diminishes perceptibly, when seen through the thicker parts of the prism, while the potassa flame is scarcely affected. In this way a few thousandths of lithia may be recognized in salts of potassa. Soda scarcely influences the result unless it is present in very large quantity.—Cartmell, Bunsen.

The spectrum of lithium (Plate I.) is characterized by the fine carmine-red line a and the faint orange-yellow line 6. If chloride of lithium is heated with alcohol and the latter be set on fire, it burns with a magnificent carmine-red color. Sodasalts disguise this reaction.

In order to discover small quantities of caesia, rubidia and lithia when associated with a large amount of potassa and soda, the dry chlorides are extracted with alcohol of 90 per cent. and a few drops of hydrochloric acid, which leaves untouched the greater share of the chlorides of sodium and potassium. The alcoholic solution is evaporated to dryness, the residue is dissolved in a little water and precipitated with bichloride of platinum. The precipitate is repeatedly boiled out with fresh quantities of water, being tested each time in the spectroscope. If rubidia and caesia be present, the spectra of these metals will shortly appear, while that of potassa becomes less marked.

The filtrate from the precipitate of platinchlorides is evaporated to dryness, the residue is gently heated in a current of hydrogen gas in order to decompose platinchloride of sodium and bichloride of platinum, it is then moistened with hydrochloric acid, dried, and the chloride of lithium is extracted with a mixture of ether and absolute alcohol. This solution, on evaporation, leaves behind chloride of lithium in a nearly pure state, which can be further tested. Before deciding from the sim ple flame that lithia is present, the dilute aqueous solution of a portion of the supposed chloride of lithium must be examined with carbonate of ammonia tc

$ 100.

c. LIME (Ca O).

1. LIME and its HYDRATE and SALTS present, in their genera deportment and properties, a great similarity to baryta and strontia and their corresponding compounds. Hydrate of lime is far more difficultly soluble in water than the hydrates of baryta and strontia; it dissolves, besides, more sparingly in hot than in cold water. Hydrate of lime loses its water upon ignition. Chloride of calcium and nitrate of lime are soluble in absolute alcohol, and deliquesce in the air.

2. Ammonia, alkaline carbonates, and phosphate of soda, present nearly the same deportment with SALTS OF LIME as with salts of baryta. Recently precipitated carbonate of lime (Ca O, C 0) is bulky and amorphous after a time, and immediately upon application of heat, it falls down and assumes a crystalline form. When recently precipitated, it dissolves pretty readily in solution of chloride of ammonium; but the solution speedily becomes turbid, and deposits the greater part of the dissolved salt in form of crystals. 3. Sulphuric acid and sulphate of soda produce immediately in very concentrated solutions of lime, white precipitates of SULPHATE OF LIME (Ca O, S O, HO+ aq.), which redissolve completely in a large proportion of water and are still far more soluble in acids. In less concentrated solutions the precipitates are formed only after the lapse of some time; and no precipitation whatever takes place in dilute solutions. Solution of sulphate of lime of course cannot produce a precipitate in salts of lime; but even a cold saturated solution of sulphate of potassa, mixed with 3 parts of water, produces a precipitate only after standing from twelve to twentyfour hours. In solutions of lime which are so very dilute that sulphuric acid has no apparent action on them, a precipitate will immediately form upon addition of alcohol.

4. Hydrofluosilicic acid does not precipitate salts of lime.

5. Oxalate of ammonia produces even in very dilute solutions of lime a white pulverulent precipitate of oxALATE OF LIME. The composition of this precipitate, when thrown down hot or from concentrated solutions, is 2 Ca O, C, O + 2 aq; whilst when thrown down cold from dilute solutions, it consists of a mixture of the above salt with 2 Ca O, C, O, + 6 aq. In very dilute solutions the precipitate forms only after some time. It is readily soluble in hydrochloric and nitric acids, but dissolves to a trifling extent only in acetic and oxalic acids.

6

6. Soluble salts of lime, when heated with dilute spirit of wine, impart to the flame of the latter a YELLOWISH-RED color, which is often confounded with that communicated to the flame of alcohol by salts of strontia.

7. Salts of lime when brought into the inner blowpipe flame or into the zone of fusion of the Bunsen lamp communicate a YEL LOW-RED color to the flame. This reaction is most evident with chloride of calcium. Sulphate of lime gives it after it has become basic. Carbonate of lime manifests it most plainly when the carbonic acid has been expelled. Compounds of lime with acids which are not volatile at a high temperature do not tinge the flame; if they are decomposed by hydrochloric acid, the coloration appears after moistening them with this acid. To promote its action, the loop of the platinum wire is flattened with a hammer, a small quantity of the substance is brought upon it and heated until it has caked together, a drop of hydrochloric acid is added, and the whole brought at once into the flame. At the moment when the drop of acid disappears the reaction is most plainly exhibited.— Bunsen.

8. Viewed through green-glass, the flame obtained as just described, appears siskin-green. This distinguishes it from strontia, which under the same circumstances has a very faint yellow color. Merz. In presence of baryta, the reaction is only manifest at the moment when the substance moistened with hydrochloric acid is brought into the flame.

9. The spectrum of lime is mapped on Plate I. The bright green line 3 and the orange line a are the most characteristic. The indigo-blue line at the right of the spectrum is only seen in a good spectroscope.

10. SULPHATE OF LIME manifests the same deportment towards alkaline carbonates and bicarbonates as sulphate of strontia.

101.

d. MAGNESIA (Mg O).

1. MAGNESIA and its HYDRATE are white powders of far greater bulk than the other alkaline earths and their hydrates. Magnesia and hydrate of magnesia are nearly insoluble both in cold and hot water. Hydrate of magnesia loses its water upon ignition.

2. Some of the SALTS OF MAGNESIA are soluble in water, others are insoluble in that fluid. The soluble salts of magnesia have a nauseous bitter taste; in the neutral state they do not alter vegetable colors; with the exception of sulphate of magnesia, they undergo decomposition when gently ignited, and the greater part of them even upon simple evaporation of their solutions. Sulphate of magnesia loses its acid at a strong white heat. Nearly all the salts of magnesia which are insoluble in water dissolve in hydrochloric acid.

3. Ammonia throws down from the solutions of neutral salts of magnesia part of the magnesia as hydrate (Mg O, H O), in form of a white, bulky precipitate. The rest of the magnesia remains