Sulphuric Acid.—Sulphuric acid disco vers, by a slight effervescence, the pre sence of carbonic acid, whether uncom bined or united with alkalies or earths.
2. If lime be present, the addition of sulphuric acid occasions, after a few days, a white precipitate.
3. Barytes is precipitated instantly, in the form of a white powder.
4. Nitric or muriatic salts, in a dry state, or dissolved in very little water, on adding sulphuric acid, and applying heat, are decomposed ; and if a stopper, moistened with solution of ammonia, be held over the vessel, white clouds will appear. For distinguishing whether ni tric or muriatic acid be the cause of this appearance, rules will be given here after.
Oxalic Acid and Oxalates.—This acid is a most delicate test of lime, which it se parates from all its combinations.
1. If a water, which is precipitated by oxalic acid, become milky on adding a watery solution of carbonic acid, or by blowing air through it from the lungs, by means of a quill or glass tube, we may in fer, that lime (or barytes, which has never yet been found pure in waters) is present in an uncombined state.
2. If the oxalic acid occasions a preci pitate before, but not after boiling, the lime is dissolved by an excess of carbonic acid.
3. If after boiling, by a fixed acid. A considerable excess of any of the mineral acids, however, prevents the oxalic acid from occasioning a precipitate, even though lime be present ; because some acids decompose the oxalic, and others, dissolving the oxalate of lime, prevent it from appearing. (Vide Kirwan on Waters, page 88.) The oxalate of ammonia, or of potash, are not liable to the above objection, and-. are preferable as to the un-.r combined acid. Yet even these oxalates fail to detect lime when supersaturated with muriatic or nitric acids ; and if such an excess; be present, it must be satu rated, before adding the test, with am monia. A precipitate will then be pro duced.
The quantity of lime, contained in the precipitate, may be known, by first ignit ing it with access of air, which converts the oxalate into a carbonate ; and by ex pelling from this last the carbonic acid, by a strong heat, in a covered crucible. According to Dr. Marcet, 117 grains of
sulphate of lime give 100 of oxalate of lime, dried at 160° Fahrenheit.
Fluate of ammonia is also a most deli cate test of lime.
•Barytic Water.-1. Barytic water is a r very effectual test for detecting the pre sence of carbonic acid, with which it forms a precipitate, which is soluble with effervescence in dilute nitric, or better in muriatic acid.
2. Barytic water is also a most sensible test of sulphuric acid and its combinati ons, which it indicates by a precipitate not soluble in muriatic acid.
.71fetals.—Of the metals, silver, bismuth, and mercury, are tests of the presence of hydro-sulphurets, and of sulphuretted hy drogen-gas. If a little quicksilver be put into a bottle, containing water impreg nated with either of these substances, its surface soon acquires a black film, and, on shaking the bottle, a blackish powder separates from it. Silver leaf and bis muth are speedily tarnished by the same cause.
Sulphate, Nitrate, and .'Icetate of Sit ver.—These solutions are all, in some measure, applicable to the same pur pose.
They are peculiarly adapted to the discovery of muriatic acid and of muri- ates, with which they form a white pre cipitate. A precipitation, however, may arise from other causes, which it may be proper to state. The solutions of silver • in acids are precipitated by carbonated alkalies and earths. The agency of the alkalies and earths may be prevented, by previously saturating them with a few drops of the same acid in which the silver is dissolved. The nitrate and acetate of silver are decomposed by the sulphuric and sulphureous acids ; out this may be prevented, by adding, previously, a few drops of nitrate or acetate of barytes, and after allowing the precipitate to subside, the clear liquor may be decanted, and the solution of silver added. Should a preci pitate now take place, the presence of muriatic acid, or some of its combina tions, may be suspected. To obviate un certainty, whether a precipitate be owing to sulphuric or muriatic acid, a solution of sulphate of silver may be employed, which, when no uncombined alkali, or earth, is present, is affected only by the latter acid.