Aquæ Stillatitiæ. E. Distilled Waters.
These are waters impregnated with the essential oils of vegetables, and are principally designed as grateful vehicles for the exhibition of more active remedies; ample directions for preparing them are given in the several Pharmacopœias, and if they be rectified by redistillation they may be kept for several years; the usual mode of preserving them is by adding spirit, which has also the incidental advantage of preventing them from being frozen during the winter season. Some recommend a film of the essential oil to be diffused over the water’s surface. They may be extemporaneously prepared by adding to water what have been called Essences, which consist of essential oil and alcohol, or by rubbing any essential oil with ten times its weight of sugar, or, what answers still better, of magnesia: when however they are so prepared they never retain their transparency. The college, in the present Pharmacopœia, have directed the distillation off the essential oil, as well as off the recent herb; this alteration is one of practical convenience. The properties of each water may be learnt by referring to the vegetable from which it is distilled.
AQUÆ MINERALES. Mineral Waters.
Although all waters that flow from the earth, are, as they contain mineral bodies in solution, strictly speaking, mineral waters, yet this term is conventionally applied to such only as are distinguished from spring, lake, river, or other water, by a peculiarity in colour, taste, smell, or any obvious properties, or by the medicinal effects which they produce, or are known to be capable of producing.
To the medical practitioner the history of these waters is most interesting and instructive, involving highly important subjects of chemical and physiological inquiry. These waters are without doubt indebted for their medicinal virtues to the operation of the substances which they hold dissolved, but this is so materially aided by the peculiar state of dilution in which they exist, as well as by the mere bulk and temperature of the water itself, as to render extremely doubtful the success of every attempt to concentrate their powers by evaporation. To what extent dilution may modify the chemical condition of saline solutions has been satisfactorily demonstrated by the researches of Dr. Murray (see Aqua Marina), and to what degree an increase in the solubility of any remedy may influence its medicinal properties has been considered at some length in the first part of this work, (page 172.) It is certain that, in general, soluble salts are capable of exerting a much more powerful effect upon the animal economy, than those which are insoluble; on which account, the earthy muriates, especially that of lime, are amongst the most active ingredients of mineral waters. Although chemical analysis has frequently from its own imperfection failed in ascertaining their presence, it seems probable that muriate of lime and sulphate of soda exist in all those springs that furnish, by the usual methods of examination, sulphate of lime and muriate of soda; for the same reasons it is equally probable that iron, which in certain waters has been supposed from the analysis to exist as a carbonate, is in its native solution a true muriate; this is undoubtedly the fact with respect to the Bath waters. Is it then surprising, that medical practitioners should hitherto have failed in their attempts to emulate, by artificial arrangements, the medical efficacy of active and mineral springs? For the investigation of the true composition of mineral waters the researches of Dr. Murray furnish a simple and elegant formula. Determine by precipitants the weight of the acids and bases, suppose them united in such a manner that they shall form the most soluble salts, and these salts will constitute the true saline constituents of the water under examination.
Mineral Waters admit of being divided into four classes, viz.
1. Acidulous; owing their properties chiefly to carbonic acid; they are tonic and diuretic, and in large doses produce a transient exhilaration; the most celebrated are Pyrmont, Seltzer, Spa, Carlsbad, and Scarborough.
2. Chalybeate; containing iron in the form of sulphate, carbonate, or muriate;[[391]] they have a styptic, inky taste: Hartfell near Moffat, Peterhead, Tunbridge, Brighton, Cheltenham, Bath, Lemington Priors, Castle Horneck, near Penzance, &c.
3. Sulphureous Waters derive their character from sulphuretted hydrogen, either uncombined, or united with lime, or an alkali: Engien, Aix la Chapelle, Harrowgate, Moffat.
4. Saline; mostly purgative, and are advantageously employed in those hypochondriacal and visceral diseases that require continued, and moderate relaxation of the bowels; Cheltenham, Leamington, Seidlitz, and all brackish waters.