43. Muriatic acid is easily detected by nitrate of sil ver, which gives a white precipitate, with water con taining a muriate. Nitrate of silver, however, gives a white precipitate, when added to water containing free alkali or sulphuric acid. If the former be present, it must he saturated with nitric acid ; if the latter exist in the fluid, it must be precipitated by baryta or its nitrate. The salt of silver likewise gives a white precipitate with carbonic acid. This, however, is soluble in nitric acid, while that occasioned by the muriatic is not. If the water contain carbonic acid, previous to adding the ni trate of silver, it will be necessary to expel it by the addition of nitric acid and boiling.
41. Boracic acid is detected by means of a salt of lead, with which it forms a white precipitate ; but as lead is precipitated by sulphuric and muriatic acids, it is necessary to remove these by means of the acetates of st•ontia and silver, having previously saturated the alkalies and earths with acetic acid.
45. The presence of an alkali, or an alkaline earth, in its free state, may be known by the green colour which it imparts to the vegetable blues, or by changing the colour of turmeric to brown. This test, however, does not point out the particular substance present. We must, therefore, have recourse to other means.
46. Potassa and soda may be distinguished from each other by two different tests, muriate of platinum and tartaric acid.
When the solution of muriate of platinum is added to water containing potassa, a yellow ish precipitate falls, which is not the case when soda only is present.
47. When tartaric acid is added to a fluid containing potassa, at first there is no visible change ; but when the acid is added in excess, a white precipitate is formed, provided the water be not in very large quantity cent• pared to that of the alkali. The precipitate formed is soluble in nitric and muriatic acids ; but tartaric acid, when added to a fluid containing soda, does not occasion any perceptible change.
In using tartaric acid as a test of potassa, the fluid must be concentrated by evaporation, otherwise the supertartrate of potassa is not deposited, being soluble in a large quantity of water. These tests also distin guish potassa from soda, when they are in combination with an acid.
48. Lime, in union with carbonic acid, is easily de tected by boiling the fluid, by which means the super abundant carbonic acid is driven off, and the carbonate of lime is deposited, the precipitate being soluble in ni tric and 'bulimic acids, and also by the addition of water containing carbonic acid. Lime, however, frequently
exists combined with a fixed acid. When this is the case, no change takes place on boiling the fluid. The most delicate test of the presence of lime, when in this state, is oxalic acid. This, when added to water Con taining a salt of lime, gives a white precipitate, which is soluble in nitric and muriatic acids. In using oxalic acid as a test of lime, we may employ either the acid pure, or in combination with ammonia. The latter, though not the most delicate, is the best, as the alkali combines with the acid with which the lime is in union, and prevents it from acting un the precipitate. If any free acid be present in the water, it must be neutralised by ammonia, and, if we have reason to suspect the pre sence of baryta, it must be precipitated by sulphuric acid. Oxalic acid, it must be remarked, likewise occa sions a precipitate with magnesia ; but the precipitation of this earth does not take place for many hours, while that with lime occurs the moment that the oxalate is added.
49. Baryta may be detected by the addition of sul phuric acid, with which it gives a white precipitate, not soluble in nitric or muriatic acid. Previous to the ad dition of the acid, it is necessary to remove the lime, as it may, if present in considerable quantity, also occasion a white precipitate with it.
50. Magnesia is precipitated by the alkalies and by lime. These tests, however, are liable to laltacy. Thus, if carbonic acid be present, and we employ lime as the test, carbonate of lime will be precipitated. If the water contain sulphuric acid, sulphate of lime may likewise be formed and deposited. When ammonia is used as the test of magnesia, if carbonic acid be present, carbonate of ammonia will be generated, which, if the water contain a salt of lime, will be decomposed, and carbonate of lime will be precipitated. In detecting magnesia, then, if we suspect the presence of the other substances mentioned, nitric acid must be added, to decompose any catbonate, and the fluid boiled. The sulphuric acid must then he precipitated by baryta.