It is supposed that considerable information may be derived with respect to the composition of mineral wa ters, from the knowledge of what are called incompa tible salts. When a certain class of salts have been procured from a mineral it is generally inferred that other salts of a peculiar nature do not exist in it. Thus it is known that the alkaline carbonates de compose the sulphates and muriates of the earths and metals ; these, therefore, it is supposed, are not con tained in the same water. The same is the case with the alkaline sulphates, and the muriates of the earths, and with sulphate of magnesia and muriatc of lime ; these decomposing each other. Much reliance cannot however be placed in this conclusion, because salts which are known to decompose each other, when their solutions are not much diluted, exist together in solu tion, if a large quantity of the solvent be present, as has been fully proved by the analysis of different mine ral waters.
By the different methods which have been pointed out, the different saline compounds of a mineral water may he procured ; of course the mode to be followed must differ according to the ingredients, which by the use of the tests we have discovered in it. When the water contains a great variety of ingredients, the me thods recommended require to be varied considerably before we can with certainty infer the presence of the different compounds. In addition to the evaporation of the fluid, and the use of alcohol, other substances must be employed to separate the saline bodies from each other, so that there may be no doubt of their na ture. The various modes followed have been particu larly illustrated by Kirwan, in his Essay on Mineral Waters.
65. Alkaline nitrates. To procure the alkaline ni trates, the water must first be freed of the sulphuric and muriatie acids, by means of acetate of baryta and acetate of silver, and then, after filtration, evaporated to dryness. Alcohol must be poured on the residue, which will dissolve part of it, and leave the nitrates probably mixed with acetate of lime. If this he present, the lime may be precipitated by dissolving the residue in water, and adding cat bonate of magnesia to the solu tion. After this the fluid must be evaporated to dryness, and the residue digested in alcohol, by which the nitrates will be left. The alkali present may be known by the use of the tests. (46, 47.) 66. Nitrate of lime. To procure the nitrate of lime, the fluid must be evaporated, but the evaporation must be stopped before any deposition takes place. Alcohol
is then to be added, which precipitates the sulphates. The fluid, after filtration, must be boiled, and the muri atic acid precipitated by acetate of silver. The fluid must be again filtered, evaporated to dryness, and the residue treated with alcohol. The solution then con tains the acetates, and probably nitrate of lime. If present, the lime may be precipitated by oxalate of am monia.
67. Xitrate of magnesia. Remove the sulphuric and muriatic acids, (65.) and evaporate to dryness. Digest the residue in alcohol, evaporate the solution to dry ness, and dissolve what is left in water ; the solution contains the acetates, and perhaps nitrate of magnesia. To this potassa must be added ; if magnesia be present, a precipitate will fall. After this the solution must be filtered, evaporated to dryness, and digested in alcohol ; if any of it remain undissolved, it is nitrate of potassa, the nitric acid of which must have been set free from the magnesia.
68. Alkaline carbonates. The presence of the carbo nates of the alkalies may he known, by the change ef fected on the vegetable colours. Should these changes not be permanent, we conclude that they are produced by ammonia. If permanent, then they are occasioned by the fixed alkalies. Whether potassa or soda, may be known by the proper tests. (46, 47.) 69. The super-carbonates of the earths and iron arc detected by boiling the fluid, by which the excess of acid is expelled, and the carbonate precipitated. The substance precipitated may be known by dissolving the residue in muriatic acid, and applying the tests. (48, 50, 53.) 70. Sulphates of potassa and soda. To procure the sulphate of soda, evaporate the fluid to about one half of its bulk, and add lime-water, till all precipitation cease ; this will throw down the earths, except lime. After this evaporate the fluid a little, and add alcohol, and then oxalic acid. After filtration add nitrate of lime. If a precipitate fall, then the solution contains sulphate of soda or potassa. These may be distin guished from each other by the tests of potassa, (46, 47.) or by adding to the solution acetate of baryta, which will throw down the sulphuric acid. Evaporate the fluid to dryness, and dissolve the residue in alcohol. Again evaporate to dryness, and expose the residue to the air. If it he acetate of potassa it will deliquesce, if acetate of soda it will effloresce.