As Those Of Spa, Pyrmont, Tunbridge, Islington, Etc

These waters discover their being impregnated with iron, by striking a blue colour with a solution of fixt alkaline salts that have been calcined with animal coals, or with a tincture made by digesting the pigment called Prussian blue in volatile alkaline spirits: this last preparation is preferable to the other, as it may be saturated more completely with that matter which tinges dissolved iron blue.

Iron in waters is discovered also by the pur-plish, bluifh, or blackish colour, which they assume on the addition of certain vegetable astringents, among which powdered galls are the most eligible. This last method of trial, which is that commonly made use of, distin-guishes as minute proportions of iron as the first, provided the liquor contains no more acid than is sufficient to keep the metal dissolved; but if the quantity of acid is very large, astrin-gents give no notice of the iron, whereas the tincture of Prussian blue discovers it universally.

Chalybeate waters appear to differ from one another, not only in the degree, but in the species, of their impregnation.

Some resemble a solution of vitriol of iron made in common spring water. Like that solution, they strike a blue or black colour with galls, deposite on standing some of their iron in an ochery form, but retain great part of it for a length of time, and yield on evaporation a saline matter, which communicates a ferrugi-neous impregnation to fresh water, and which* appears to be a true vitriol of iron. From some waters, as that of Hartfell in Scotland, the vitriol has been crystallized (a) in its proper form.

Others resemble a solution of the same vitriol with an admixture of natron or the mineral fixt alkaline salt. Like such a mixture(b), they strike, when fresh, a purple colour with galls, deposite the whole of their iron in a very little time, and yield on evaporation, not a vitriol or chalybeate salt, but a salt composed of the acid of vitriol and alkali: some, as that of Geron-sterre at Spa, yield also a little pure alkali (c), besides what is satiated with acid. It may be observed, that in artificial mixtures of alkalies with solutions of vitriol, or other metallic solutions made in acids, (and possibly something of the same kind may obtain also in the natural,) if the vessel is immediately stopt, fo as to have no vacuity after the instant of mixture; the acid and the alkali have no action on one another so long as they are kept confined, that is, so long as the extrication of air, the common concomitant of their mutual action, is prevented: but as soon as the vessel is opened, or the contained air has an opportunity of escaping, the alkali begins to absorb the acid, a sparkling or effervescence ensues, greater or less in proportion to the quantities of the two, and the metal, thus diverted of its acid solvent, precipitates (a).

(a) Edinb. ess. and ohs. phys. & lit. i. 346.

(b) That an alkaline addition is necessary, to make solutions of vitriol strike with galls the purple colour that chalybeate waters do, is a discovery of Mr. Reynolds, exper. on a chalybeate water near Bromley in Kent.

(c) Rutty, synops. 323.

It is not however to be presumed, that the speedy separation of the ferrugineous matter of waters is owing universally to an alkaline precipitant. Solutions of pure vitriol in pure water deposite a part of their iron spontaneously; and if the solutions be so far diluted, as to strike with astringents a colour little more than perceptible, they will lose so much in a few hours as to exhibit with the same astringents no tinge at all.

In general, a blue or black colour produced with galls may be looked upon as a mark of the absence of alkaline salt; and a purple, as a mark that either the water originally contained an alkali, or has become alkalescent or verging to putrefaction by Handing. On the same principle, a degree of alkalescence, or of tendency to corruption, in common waters, very far too minute to be sensible on any other known trial, may be made conspicuous; viz.

(a) A discovery of Mr. Scheffer, Suenska vetensk. acad. handl. 1753.

by the water, when impregnated with a little vitriol, as a grain or two to a pint, striking a purple colour with galls.

The spontaneous reparation of the iron, which happens in many of the chalybeate waters, and which, though it may be retarded, cannot be prevented by any care in flopping the bottles, after the waters have been once exposed to the air, renders them unfit for long keeping or carriage. A small addition of any acid prevents the separation, even in those whose virtues are naturally the most fugitive: it is suspected, that the chalybeates brought from Germany have commonly this artificial impregnation.

These waters are used, like other chalybeates, in debilities and laxities of the stomach, chylo-poietic organs, and of the viscera in general; in decays of constitution; in cachectic, chloro-tic, and other like indispositions. Where they pass freely, they are accounted more invigorating than the artificial preparations of iron, and less liable to disorder particular constitutions: many of them however are more apt to fail of taking due effect, on account perhaps of the acid solvent being more disposed to quit the metal. Some of them are rarely observed, and some scarcely ever, to give any black tinge to the feces, though drank in large quantity; a phenomenon which may perhaps be ascribed to their depositing their iron in the first passages in an indissoluble and inactive state, rather than to the cause which some have assigned, then-carrying it entire into the blood. They are taken to the quantity of two or three pints or more in a day, divided into different doses; and require the same caution in their use as the artificial chalybeates.