WATERS, mineral. The complete and accurate analysis of mineral waters is one of the most difficult subjects of chemical research, and requires a very extensive acquaintance with the properties and ha bitudes of a numerous class of substances. Such minuteness, however, is scarcely ever required in the experiments that are subservient to the ordinary purposes of life, a general knowledge of the compo sition of bodies being sufficient to assist in directing the most useful applications of them. Instead, therefore, of giving a very ample detail of all the methods pointed out by Kirwan and others, we shall describe the means which arc most generally useful in researches of this kind.
Before any proceeding is made in the analysis of a water, it is proper to in quire into its natural history, and to ex amine attentively its physical characters. The temperature of the water must be carefully observed, and the quantity in quired into, which it' yields in a given time. The sensible qualities of taste, smell, degree of transparency, &c. are also best entertained at the fountain head. The specific gravity of the water must also be found. See GRAVITY, specific. The readiest way of judging of the con tents of mineral waters is by applying tests or re-agents, the chief of which are the following : Infusion of litmus is a test of most un combined acids.
if the infusion redden the unboiled, but not the-boiled water, we may infer, that the acid is volatile, and most proba. bly, the carbonic. Sulphuretted hydrogen gas, dissolved in water, also reddens lit mus, but not after boiling.
To ascertain whether the change be produced by carbonic acid, or by sulphu retted hydrogen, when experiment shows that the reddening cause is vola tile, add barytic water. This, if carbonic acid be present, will occasion a precipi tate, which will dissolve, with efferves cence, on adding a little muriatic acid. Sulphuretted hydrogen may also be con tabled, along with carbonic acid, in the same water ; which will be determined by the tests hereafter to be described, Paper tinged with litmus is also redden ed by the presence of carbonic acid, but regains its blue colour on drying.
• Infusion of Litmus reddened by Phospho ric acid,—Tincture of Brazil-wood, Tincture of Turmeric, and Paper stained with each of these three Substances,—Tinc ture of Red Cabbage.—All these tests have one and the same object.
Infusion of litmus, reddened by phos phoric acid, or litmus paper reddened by it, has its blue colour restored by alkalies and earths, and by carbonated alkalies,. and carbonated earths. Turmeric paper and tincture are changed to a reddish brown by alkalies, whether freed from carbonic acid or not ; by earths, freed from carbonic acid, but not by carbonated earths.
The red infusion of Brazil-wood, and paper stained with it, become blue by alkalies and earths, and even by the lat ter, when dissolved by an excess of car bonic acid. In the last mentioned case, however, the change will either cease to appear, or will be much less remarkable, when the water has been boiled.
Tincture of cabbage is, by the same causes, turned green ; as is also paper stained with the juice of the violet, or with the scrapings of radishes.
Tincture of galls.—Tincture of galls is employed for discovering iron, with which it produces a black tinge. The iron, however, in order to be detected by this test, must be in the state of a red ox ide, or, if oxydized in a less degree, its effects will not be apparent, unless after standing some time in contact with the air. By applying this test before and after evaporation, or boiling, we may know whether the iron be held in solu tion by carbonic acid, or by a fixed acid ; for, 1. If it produce its effect before the application of heat, and not afterward, carbonic acid is the solvent.
2. If after, as well as before, a fixed and vulgarly called mineral acid is the solvent.
3. If, by the boiling, a yellowish pow der be precipitated, and yet galls continue to strike the water black, the iron, as often happens, is dissolved, both by carbonic acid gas and by a fixed acid.