and the residue treated afresh with water, a perfect separation of the lithium is effected. This salt is a white powder.

Its composition is said to be variable: some analyses give the formula LiNaHPO1.

It is nearly insoluble in water containing phosphate of soda, scarcely soluble in cold water, but more so in hot. It dissolves in dilute nitric acid. THE SILICOFLUORIDE is insoluble.

The distinguishing features by which lithium salts are recognized are practically these,--the carmine-coloured blowpipe flame, and the very insoluble phosphate of lithium and sodium.

SECTION II.-Bodies readily volatilized by ignition.

SALTS OF AMMONIUM.

Solution for the reactions:-chloride of ammonium (NH ̧Cl) in water.

Ammonium (NH) is the first compound metal with which the student has to deal. It is not known in the separate state, but the salts in which it exists are very numerous: they are all proto-salts, 1 equivalent of NH, being equal to 1 equivalent of H; in other words, the basic radical ammonium is monatomic. All these salts are colourless, unless their constituent acid-radical is coloured; they are not actively poisonous unless their acid-radical has very poisonous properties.

When heated, ammonium salts entirely volatilize, and in so doing impart no colour to the flame (the chloride indeed tinges the flame blue, but this is due to the chlorine).

They may, however, be immediately recognized by their behaviour when warmed gently with hydrate of potassium (KHO); a double decomposition occurs, thus,

NH,C1+KHO=KC1+NH HO.

The hydrate of ammonium thus produced decomposes into water (H2O) and ammonia gas (NH,). This gas has a most peculiar pungent odour, termed ammoniacal, but better known as that of hartshorn, or spirits of sal-volatile. The pungent odour is sufficient to reveal the presence of this gas, which may also be detected by holding over the mouth of a test-tube from which it is

issuing, a stout rod moistened with concentrated hydrochloric or acetic acid, when dense white fumes will be seen about the rod, instead of the ordinary almost transparent vapour of the acid; this effect is due to the formation of an ammonium salt,

NH,+HCl=NH,Cl,
White fume.

The principal insoluble salt by which this metal is recognized is the chloroplatinate.

The Chloroplatinate is produced by the action of chloroplatinic acid (HPtCl,) on solutions of ammonium salts. It is a yellow crystalline precipitate, resembling the corresponding potassium salt in being octahedral, and belonging to the regular system. Its formula is NH1 PtCl.

It is very insoluble in cold water, but more so in hot; it is still more insoluble in alcohol, 1 part requiring 1405 parts of rectified spirit for its solution. It is more soluble in dilute acid than in pure water.

THE PERCHLORATE and the CARBAZOTATE are soluble.

THE ACID TARTRATE is only produced by tartaric acid (H2T), when added to very concentrated solutions of ammonium salts, especially of the hydrate. It is a white crystalline precipitate of the same form as the corresponding potassium compound.

It is as readily soluble in the hydrate of ammonium (NH, HO) as the potassium salt is in hydrate of potassium (KHO), the very soluble neutral tartrate being thereby formed. It is rather insoluble in cold water, but dissolves freely in boiling water; it is more insoluble in alcohol, and more soluble in acids. THE SILICOFLUORIDE is soluble.

The tests to be actually employed for the detection of ammonium obviously are, the volatility of the salt, its ammoniacal odour when heated with solution of hydrate of potassium (KHO), or when mixed with moist hydrate of calcium (CaHO), and its precipitation by chloroplatinic acid.

In order to avoid too much verbal recapitulation, and to show the student the method of consecutively applying the tests above mentioned when searching either for one or more of the basic radicals which the subdivision contains, the Table on the following page is annexed. Tables, it must be remembered, are not guides to be followed blindly, but only indications of the kind of course which the student should pursue in analysis; the best can after all be but descriptions of one series of methods, of which several may be equally good for the attainment of the same end; and the student should bind himself to no one formula, but seek frequently to vary his method of analysis by adopting other sequences of experiments. Greater scope will be afforded him in the succeeding subdivisions than in the present one for so doing; and in the Tables which will be appended to each, we shall not always select that which is believed to be the best method of distinguishing a substance, if a slightly inferior one is more striking. Tables, nevertheless, which contain the most accurate methods are of great value, and a complete series of such will be found in the second part of the present volume: they will be constructed upon the position that all the substances occurring in their respective subdivisions are present, whilst in those appended to each subdivision it will be assumed that one member only is to be detected.

sup

Analysis of Subdivision I.

The salt may be one of POTASSIUM, SODIUM, LITHIUM, or AMMONIUM.

Ignite the substance; if nothing volatilizes, we infer the

absence of Ammonium, and confirm it by gently warming a fresh portion of the original substance with solution of hydrate of potassium.

presence of

Potassium, Sodium, or Lithium.

Dissolve a portion of the ignited salt in a few drops of water, add one drop of hydrochloric acid and a few drops of bichloride of platinum, and stir; if no precipitate is produced, even after the addition of alcohol, and the lapse of some time, we infer the

SALTS OF BARIUM, STRONTIUM, AND CALCIUM; AND OF MAGNESIUM.

One great distinction between this and the first subdivision may be at once pointed out; it is this: that a far smaller number of the salts of these metals is soluble in water; and among the insoluble, or nearly insoluble salts, are found the sulphates, carbonates, oxalates, and phosphates, nearly all of which are easily soluble in the first group, nearly all almost insoluble in the present. It is, however, especially to be remembered, that among the soluble salts of this subdivision the oxides and sulphides are ranked, because this constitutes a distinguishing feature between the first two and the last two subdivisions. If we desire to separate the metals of this group from those of the preceding one, we have only to form their carbonates, oxalates, or phosphates;

the metal is thus precipitated in an insoluble combination, and being collected on a filter, the clear liquid passing through will contain the salts of the first subdivision. The way in which these insoluble salts are formed, is by adding a soluble salt of the required acid-radical to the solution which we wish to precipitate; now almost the only soluble salts of the acid-radicals in question are the hydrogen salts (the so-called acids), and the salts containing the metals of the first subdivision (the alkaline salts); of these, for reasons which will soon be obvious, we prefer to employ the ammonium salts, and of the ammonium salts the neutral carbonate (NH),CO, is the most advantageous. Any salt thus chosen as the precipitant of an entire group is commonly called the group-test or group-reagent; in fact, we find in every subdivision that there is a certain reagent which precipitates every member of the group, to which this name of groupreagent has been applied. Afterwards other reagents are used, some of which exercise their action on several members, some on individuals only. Subdivision I. has no such general reagent; the entire group is not precipitated by any single substance, we are therefore obliged to resort to particular or special tests.

Certain conventional expressions are attached to the compounds of this subdivision also. Their oxides and hydrates are called "the alkaline earths," and their other salts "the salts of the alkaline earths."

The three first members of the subdivision bear a very strong resemblance to each other; their salts are for the most part colourless, except in those cases where the acid-radical is coloured. The compounds of barium are very poisonous, but those of strontium and calcium are not so. The fourth member, magnesium, differs in many respects from the others, many of its salts are far more soluble in water; this difference is strikingly exhibited in the case of its sulphate, which is an extremely soluble salt, while the sulphates of the other three metals are almost insoluble.

The second subdivision is as readily broken up into two parts or sections as the first, although by different means.