ANALYTICAL CHART FOR ONE OR MORE COMMON METALS. 135

Add hydrochloric acid, and filter.

The student should practise the examination of solutions containing the above metals until he is able to analyze them with facility and accuracy. In this way he will best fix on his mind the peculiarities of each element and their general relations to each other. As the rarer metals are not included here, the tables are by no means complete analytical schemes; practical remarks concerning them, therefore, are, for the present, deferred.

METALS OF MINOR PHARMACEUTICAL

IMPORTANCE.

Thus far has been considered, somewhat in detail, the chemistry of the common metals, salts of which are frequently used in medicine or in testing medicinal substances. These

There still remain eleven metals, eight of which are mentioned in the British Pharmacopoeia, namely

Lithium,

Chromium, Gold,

Cadmium,

Manganese, Tin,

Platinum, Bismuth.

Compounds of the remaining three are sufficiently common to occasionally come under the notice of any student of chemistry :—

These eleven metals of minor pharmaceutical interest may be shortly studied, a few only of the reactions of each being performed. When all have been thus treated, their respective positions in the analytical groups will be indicated and a tabular scheme be given by which an analysis of a solution containing any metal may be effected. Thus, step by step, we may learn how to analyze almost any substance that may occur, and know to what extent the presence of a rarer will interfere with the ordinary tests for a common element; additional illustrations of the working of chemical laws will be acquired, and the store of chemical and pharmaceutical facts increased. opportunity thus afforded for improvement in habits of neatness in manipulation, precision, and classification is another and no mean reason why such experiments should be prosecuted, the direct value of which may not be considerable,

The

LITHIUM.

Symbol L. Atomic weight 7.

Lithium is widely distributed in nature, but usually in minute proportions compared with other elements. A trace of it may be found in most soils and waters, a Cornish spring containing even considerable quantities as chloride. The salt chiefly used in medicine is the Citrate (L,CH,O,) (Lithia Citras, B. P.), which is prepared by dissolving the Carbonate (LCO) in citric acid. 2L,CH2O, + 3H ̧0 + 3C0,

Carbonate of lithium.

=

¡Carbonic acid gas.

The carbonate (Lithia Carbonas, B. P.) is obtained from the minerals which contain lithium-namely, lepidolite (from Xeris, lepis, a scale, and Xíos, lithos, a stone; it has a scaly appearance), triphane (from Tpeîs, treis, three, and paivw, phaino, I shine) or spodumene (from orodów, spodoo, to reduce to ashes, in allusion to its exfoliation in the blowpipe-flame), and petalite (from Téradov, petalon, a leaf; its character is leafy and laminated). Each contains silicate of aluminium, with fluoride of potassium and lithium in the case of lepidolite, and silicate of sodium and lithium in the others. Liquor Lithia Effervescens, B. P., is a solution of carbonate of lithium in water charged with carbonic acid.

Urate* of lithium is more soluble than urate of sodium; hence lithium preparations are administered to gouty patients in the hope that urate of sodium, with which such systems are loaded, may be converted into urate of lithium and removed.

In chemical position lithium stands between the alkaline and the alkaline-earth metals, its hydrate, carbonate, and phosphate being slightly soluble in water. Its atom is univalent.

Analytical Reaction.-Moisten the end of a platinum wire with solution of a minute particle of solid lithium salt, and introduce it into an air gas- or other slightly coloured flame (spirit-lamp or blowpipe-flame); a magnificent crimson tinge is imparted to the

flame.

The light emitted by ignited lithium vapour is of a purer scarlet * Urates are salts of uric acid, which will be considered subsequently.

When the

than that given by strontium, the next element. flames are examined by spectrum analysis (physically analyzed by a prism), the red rays are, in the case of strontium, found to be associated with blue and yellow, neither of which are present in the lithium light.

STRONTIUM.

Symbol Sr. Atomic weight 87.5.

Strontium is not widely distributed in nature; but the carbonate (SrCO,), known as strontianite, and the sulphate (SrSO), known as celestine (from cælum, the sky, in allusion to its occasional bluish colour), are by no means rare minerals.

Salts of strontium are not employed in medicine. They are chiefly used by firework-manufacturers in preparing red fire. The colour they impart to flame is a beautiful crimson-ignited strontium vapour emitting red rays, as already explained. Nitrate of strontium (Sr2NO,) is best for pyrotechnic compositions, its oxygen enabling it to burn freely when mixed with charcoal, sulphur, &c. It, or any salts, may be obtained by dissolving the carbonate in the appropriate acid, or by igniting the cheaper sulphate with coal, whereby sulphide (SrS) is produced, and dissolving this in acid.

The position of strontium among the chemical elements is between barium and calcium; its sulphate is very sparingly soluble in water. Its atom, like those of barium and calcium, is bivalent (Sr").

Analytical Reactions.

First Analytical Reaction.-To solution of a strontium salt (Sr2NO,, SrCl,, &c.) add carbonate of ammonium; a white precipitate of carbonate of strontium (SrCO) falls.

Second Analytical Reaction. To a solution of a strontium salt add sulphuric acid previously so diluted that it will not precipitate calcium salts, or an equally dilute solution of a sulphate; a white precipitate of sulphate of strontium (SrSO) falls. The formation of this precipitate is promoted by stirring and by setting the liquid aside for some time.

Barium is precipitated immediately under similar circumstances.