Class V, two or three teaspoonfuls of carbonat nium (App., § 18) and boil the solution. A whit of carbonate of calcium will be produced. A allow the precipitate to settle until the upper p liquid is comparatively clear. To this clarified p fresh drop of carbonate of ammonium. If this an additional precipitate, more carbonate of amn be added, and the boiling repeated. To the parti liquid add again a drop of carbonate of ammo process of making sure of the complete precipi calcium is essentially the same as that prescribe itating the last class, and is, indeed, of general When the precipitation of the calcium has been p complete, filter the whole liquid, and receive the small evaporating-dish. Calcium is separated in carbonate under these circumstances, because th is almost insoluble in weak alkaline liquids, wh of carbonate of ammonium is present. The all barium and strontium behave in the same way, s three elements, viz., barium, strontium and calci a new class Class VI, whose complete treat forth in Chapter VII.

12. Definition of Class VII. Of the twe tallic elements, which were to be classified (§ 6) remain, viz., magnesium, sodium and potassium vious that these three elements could not have solution through all the operations to which liquid has been submitted, unless their chlori phides had been soluble in weak acids, and the hydrates), sulphides and carbonates soluble in monia-water, at least in presence of dilute, ammonium salts. It is a fact that all these co sodium and potassium are soluble in water, and i alkaline, and saline solutions; the magnesium been partially precipitated in Classes IV, V and

2

14

SEPARATION OF CLASSES.

§§ 12, 13

the presence of ammonium salts in the solution. These three elements constitute Class VII.

Evaporate the filtrate from Class VI until it is reduced to one half or one third of its original bulk. Pour a smal! part of the evaporated filtrate into a test-tube; add a little ammonia-water and a teaspoonful of phosphate of sodium (App., § 26), and shake the contents of the tube violently. Sooner or later a crystalline precipitate will appear. This peculiar white precipitate of phosphate of magnesium and ammonium identifies magnesium; but as we have added a reagent containing sodium, the filtrate is useless for further examination. The liquid remaining in the evaporating-dish is then evaporated to dryness, and moderately ignited until fuming ceases. All the ammoniacal salts which the solution contained will be driven off by this means, and there will remain a fixed residue, in which are concentrated all the salts of magnesium and sodium which the solution contained. In this case we have already proved the presence of magnesium; it remains to indicate briefly the nature of the means used to detect the sodium.

Dissolve the residue in the dish, or a portion of it, in three or four drops of water. Dip a clean platinum wire (App., § 79) into this solution, and introduce this wire into the colorless flame of a gas or spirit-lamp (App., § 74). An intense yellow coloration of the flame demonstrates the presence of sodium. A violet coloration would have proved the presence of potassium. Magnesium compounds, when present, have no prejudicial effect on these characteristic colorations. The means of detecting each member of this last class in presence of the others will be found described in Chapter VIII.

13. A condensed statement of the classification illustrated by the foregoing experiments is contained in the table on the next page. All the common metallic elements are embraced in it. The place of the precious metals gold and platinum is also indicated. The classification itself would

16

SEPARATION OF CLASSES.

§§ 14, 15

not be essentially different, if all the rare elements were comprehended in it. The general subdivisions would be the same, although some of them would embrace many more particulars.

14. It is essential to success to follow precisely the prescribed order in applying the various general reagents. Class I would go down with Class II, were chlorhydric acid forgotten as the first general reagent. Class II would be precipitated in part with Class IV and in part with Class V if sulphuretted hydrogen were not used in its proper place. A large number of the members of the first five classes would be precipitated as carbonates with Class VI, were they not previously eliminated by the systematic application of chlorhydric acid, sulphuretted hydrogen, ammonia-water and sulphydrate of ammonium in the precise order and under the exact conditions above described. It should be noticed that all the general reagents are volatile substances, which can be completely removed by an evaporation to dryness followed by a very moderate ignition.

15. The series of experiments just completed is merely intended to demonstrate the principles in accordance with which these twenty-two common elements are classified for the purposes of qualitative analysis. The general plan is here sketched; the practical details, essential to success in the conduct of an actual analysis, will be given hereafter.

CHAPTER II.

CLASS I.-ELEMENTS WHOSE CHLORIDES A
BLE IN WATER AND ACIDS.

16. Example of the Precipitation of the Class I. Place in a test-tube five or six drops concentrated aqueous solution of nitrate of s § 62), an equal quantity of a solution of merc and two teaspoonfuls of a solution of nitrate case the solution becomes turbid through the a bonic acid dissolved in the water, pour in one of nitric acid to destroy the cloudiness.

Add dilute chlorhydric acid to the solution, d and shake the mixture thoroughly after each ad acid, until the fresh portions of the latter cease precipitate on coming in contact with the compa liquor which floats above the insoluble chlorid add three or four more drops of the acid to ins ence of an excess of it in the solution.

17. Analysis of the Mixed Chlorides. method of separating the chlorides of lead, sil cury, one from another, depends upon the facts: chloride of lead, though but little soluble in co solves readily in boiling water, while chloride subchloride of mercury (mercurous chloride, Hg good as insoluble in that liquid; 2d. That chlo is soluble in ammonia-water; and 3d. That me ride is discolored by ammonia-water without diss To effect the separation: Collect upon a cipitate produced by chlorhydric acid, allow it rinse it with a few drops of cold water. Place tube beneath the funnel which contains the filte

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