was originally formed, how the basylous and acidulous radicals were originally distributed. In attempting this, much must be left to theoretical considerations; but a process by which the salts themselves are separated is of trustworthy practical assistance; hence the chief advantage of analyzing separately the solutions resulting from the action of water, acids, &c. on a solid substance.

If the salt or any part of a mixture of salts is insoluble in water, hydrochloric acid, and nitric acid, digest it in nitro-hydrochloric acid, boiling if necessary; evaporate to remove excess of acid, dilute, and proceed as before.

Sulphide of mercury and substances only slowly attacked by hydrochloric or nitric acid, such as calomel, ignited ferric oxide, &c. are sufficiently altered by the free chlorine of aqua regia to become soluble.

If the substance is insoluble in water and acids, it is one or more of the following substances:-Sand and certain silicates, such as pipeclay and other clays, fluorspar, cryolite (3NaF,AIF ̧); sulphates of barium, strontium, and possibly calcium; tinstone; glass; felspar (double silicate of aluminium and other metals); chloride of silver; sulphate of lead. It may also be or contain carbon or carbonaceous matter, in which case it is black and combustible, burning entirely or partially away when heated in the air; or be or contain sulphur, in which case sulphurous gas is evolved, detected by its odour, when the substance is exposed to heat. For the other substances proceed according to the following (Bloxam's) method:

Four or five grains of the substance are intimately mixed with twice the quantity of dried carbonate of sodium, and this mixture well rubbed in a mortar with five times its weight of deflagrating flux (1 of finely powdered charcoal to 6 of nitre). The resulting powder is placed in a thin porcelain dish, or crucible, or clean iron tray, and a lighted match applied to the centre of

the heap. Deflagration ensues, and decomposition of the various substances occurs, the acidulous radicals going to the alkalimetals to form salts soluble in water, the basylous radicals being simultaneously converted into carbonates or oxides. The mass is boiled in water for a few minutes, the mixture filtered, and the residue well washed. The filtrate may then be examined for acidulous radicals and aluminium in the usual way, and the residue dissolved in dilute hydrochloric acid and analyzed by the ordinary method.

The only substance which resists this treatment is chrome iron-ore.

To detect alkali in felspar, glass, or cryolite, Bloxam recommends deflagration of the powdered mineral with one part of sulphur and six of nitrate of barium. The mass is boiled in water, the mixture filtered, hydrate and carbonate of ammonium added to remove barium, the mixture again filtered, and the filtrate evaporated and examined for alkalies by the usual process.

QUALITATIVE ANALYSIS OF SUBSTANCES HAVING UNKNOWN PROPERTIES.

Substances are presented to the analyst in one of the three forms in which all matter exists-namely, solid, liquid, or gaseous.

The method of analysis in the case of solid bodies has just been described (pp. 242 & 244).

In the case of liquids, the solvents as well as the dissolved matters claim attention. A few drops are evaporated to dryness on platinum foil to ascertain if solid matter of any kind is present; the liquid is tested by red and blue litmus paper to ascertain if free alkalies, free acids, or neither are present; a few drops are heated in a test-tube and the odour of any vapour noticed, a piece of glass tubing bent to a right angle being, if

necessary, adapted to the test-tube by a cork in the ordinary way, and some of the distilled liquid collected and examined; finally, the usual group-reagents for the several basylous and acidulous radicals are consecutively applied.

Proceeding in this way the student, who has already had some experience in pharmacy, will not be likely to overlook such solvents as water, acids, alcohol, ether, fixed oils, essential oils, &c., nor to miss the substances which these menstrua may hold in solution. He must not, however, suppose that he will always be able to qualitatively analyze, say, a bottle of medicine; for the various infusions, decoctions, tinctures, wines, syrups, liniments, confections, extracts, pill-masses, and powders contain vegetable matters most of which at present are quite beyond the reach of the analyst. Neither the highest skill in analysis nor the largest amount of experience concerning the odour, appearance, taste, and uses of drugs is sufficient for the detection of all these vegetable matters. Skill and experience combined will, however, do much; and even so difficult a task as that just mentioned may be, in most cases, accomplished with reasonable success. Qualitative analysis alone will not enable the experimenter to produce a mixture of substances similar to that analyzed; to this end recourse must be had to quantitative analysis, a subject reserved for subsequent consideration.

Gas-analysis, or Eudiometry (from evdia, eudia, calm air, and perpov, metron, a measure, in allusion to the eudiometer, an instrument used in measuring the proportion and, as the early chemists thought, the salubrity of the gases of the air), is a branch of experimental investigation, chiefly of a quantitative character, concerning which information must be sought in other treatises. The analysis of atmospheric air from various localities, coal-gas, and the gases obtained in chemical researches involves operations which are scarcely within the sphere of Pharmaceutical Chemistry. Beyond the recognition, therefore, of oxygen, hydrogen, nitrogen, carbonic, sulphurous, and hydrosulphuric acid gases, the experimental consideration of the chemistry of gaseous bodies may be omitted. Their study should not, however, be neglected, as existing conceptions of the constitution of chemical substances are largely dependent on the observed relations of the volumes of gaseous compounds to their elements. The best work on this subject is a small book by Hofmann, • Introduction to Modern Chemistry.'

Spectrum-Analysis.-It may be as well to state here that the preliminary and final examinations of minute quantities of solid matter may, in certain cases, profitably include their exposure to a temperature at which they emit light, the flame being physically analyzed by a spectroscope. A spectroscope consists essentially of a prism to decompose a ray of light into its constituent colours, with tubes and lenses to collect and transmit the ray or rays to the eye of an observer. The material to be examined is placed on the end of a platinum wire, which is then brought within the edge of a spirit-lamp or other smokeless flame; volatilization, attended usually in the case of a compound by decomposition, at once occurs, and the whole flame is tinged of characteristic hue. A flat ribbon of rays is next cut off by bringing near to the flame a brass tube, the cap of which is pierced by a narrow slit. At the other end of the tube, at focal distance for parallel rays, is a lens, through which the ribbon of light passes to a prism; the prism decomposes the ribbon, spreading out its constituent colours like a partially opened fan, and the spectrum thus produced is then examined by help of a telescope attached by a moveable joint to the stand which carries the prism and object-tube. Sodium compounds, under these circumstances, give yellow light only, indicated by a double band of light in a position corresponding to the yellow part of an ordinary solar spectrum. The potassium spectrum is mainly composed of a red and violet band; lithium a crimson, and at very high temperatures a blue band. Most of the other elements give equally characteristic spectra.

SPECIAL CHEMICAL OPERATIONS ON SUBSTANCES OF VEGETABLE AND

ANIMAL ORIGIN.

Except alcohol and a few acids, the compounds which have hitherto engaged our notice have been of mineral origin. But many medicinal substances, obtained from animals and vegetables, when discovered were producible only by highly organized living structures, and were hence termed organic compounds*.

A few of these compounds, of common occurrence in pharmacy and possessing prominent characteristics, may now occupy attention; reactions of the alkaloids and some other principles may be performed, and the methods of examining morbid urine be experimentally studied. There will then remain certain substances, solid and liquid, which can only be fairly regarded from a synthetical point, and a still larger number, doubtless, not yet brought within the grasp of the chemist, and of which, therefore, we must at present be content to remain in ignorance. An opportunity, however, will be afforded of noticing the effect of a mixture of definite and indefinite organic matter, such as a vomit or the contents of a stomach, in masking or preventing the reactions by which mineral and vegetable poisons are detected.

ALKALOIDS.

The alkaloids, or alkali-like (eidos, eidos, likeness) bodies have many analogies with ammonia. Their constitution is not yet

*

A large number of these compounds can now be obtained artificially-without the aid of a living organism; hence the distinction formerly drawn between organic and inorganic compounds, organic and inorganic chemistry, is fast breaking down.