Many mineral waters possess active properties, for which, however, we cannot account, on the known properties of the compounds discovered in them. Thus the Bath waters, according to the analysis by evapora tion, contains in an English pint about 9 grains of sul phate of lime, 3.3 muriate of soda, 3 sulphate of soda, a--5ths of carbonate of lime, silica, and oxide of iron. These are either so inert, or in so small quantity, as to be incapable of producing any effects on the liv ing system. According to Dr. Murray, the true com ponent parts of the Bath water are very different. It contains muriate of lime, a substance possessed of con siderable power, along with mum iate of iron. The quan tity of muriate of lime, equivalent to 3.3 of muriate o? soda, is 3.1. A pint, therefore, of the Bath water, if the views of Murray be correct, contains 3.1 gr. of this active agent. If this he the ease, we can perhaps ac count for its medicinal properties.
The opinions entertained by Dr. Nlurray, as just ex plained, afford another method of analysing mineral waters.
in analysing a mineral water. according to the mode recommended by Al urray, we must first, by the use of the various tests already described, ascei tain the differ ent substances which it contains. We then infer that these exist in it in a state of combination, so as to form the most soluble salts.
This method of ascertaining the quantity of saline compounds in water, was previously employed by Dr.
Marcet, in his analysis of the water of the Dead Sea, published in the Philos°'dical Transactions for 1807. Dr. Marcet does not, however, state, that he supposed the ingredients were so combined as to form the most soluble salts.
Dr. Murray has given the following formula, which is applicable to almost all mineral waters.
The four classes of mineral waters, the acidulous, the sulphureous, the chalybcate, and the saline, may all be reduced under the last. By the application of caloric, the gaseous fluids are driven off from the two first, and the iron may be precipitated from the third by its pro per test. The substances left after this are the same as those contained in saline mineral waters.
The substances which usually exist in saline mineral waters, are carbonic, sulphuric, and muriatic acids, with soda, lime, and magnesia. Suppose that in the water to be analysed all of these have been detected, the fluid must be evaporated, stopping the evaporation be fore there is any deposition from it. Muriate of baryta is then to be added, as long as any precipitate falls, carefully avoiding adding an excess. If the precipi tate be soluble with effervescence in murialic acid, it is carbonate of baryta. The weight of this gives that of the carbonic acid 100 gr. = 22 of acid. If the preci pitate do not effervesce with muriatic acid, it is sul phate of baryta, 100 gr. of which = 34 of sulphuric acid. If the precipitate be partially soluble in muriatic acid, it contains both carbonate and sulphate of baryta ; the proportions of each of which may be known, by weighing the precipitate, washing it with muriatic acid, and drying the residue. The weight of this gives that
of the sulphate, the loss that of the carbonate of baryta. By this means the carbonic and sulphuric acids are re moved, and the whole of the salts are converted to mu riates. Oxalate of ammonia is next to be added to the filtered fluid. Oxalate of lime is precipitated, which, after being exposed to a strong heat, must be converted into sulphate. (62.) 100 g. = 41.5 of lime.
The filtered fluid is afterwards to be heated to about and reduced a little by evaporation. A solution of carbonate of ammonia is then to be added to it, and immediately afterwards a solution of phosphate of am monia, continuing the addition of both as long as there is any precipitation, taking care to leave an excess of ammonia. By the addition of these substances, one part of the ammonia neutralises the muriatic acid of the muriate of magnesia, the other portion combines with the phosphoric acid and the magnesia, and forms the triple phosphate of magnesia and ammonia which is precipitated. By exposing this to a red heat for an hour it is converted into phosphate of magnesia, 100 gr. of which = 40 magnesia. After this the fluid contains muriate of soda, perhaps with muriate of ammonia. To procure the former it must be evaporated to dryness, and the residue exposed to a high temperature, 100 = 53.3 soda.
The muriatic acid in the muriate of soda obtained may be either greater or less than what was contained originally in the fluid; part of the soda may have been disengaged from the other acids, and have combined with the muriatic acid of the muriate of baryta, used in the precipitation of the sulphuric and carbonic acids. If this be the case, the acid in the muriate of soda pro cured will be greater than what existed in the water ; or the soda may be in less quantity than could neutral ize the whole of the muriatic acid, part of this acid hay ing been combined with the other bases. If this be the case, the acid set free during the addition of the ammo niacal salts would be contained in the residue of the evaporation in union with ammonia, but would be vo latilized by the heat, the muriatic acid in the muriate of soda would therefore be less than the water originally contained. Though the quantity of muriate of soda procured, therefore, gives the real quantity of the soda, yet it does not afford the proportion of the muriatic acid. This may be discovered, by combining by cal culation the bases with the acids, taking the quantity of muriatic acid in the muriate of soda, and thus we will find whether there be a deficiency or redundance of muriatic acid. By subtracting the surplus from what exists in the muriate of soda, or by adding the deficiency to it, we arrive at the quantity of the muriatic acid. This method is, however, liable to fallacy. It is better, therefore, to take a separate portion of the water, eva porated to the proper strength, and remove the carbonic and sulphuric acids by means of nitrate of baryta, and then add nitrate of silver to it, by which we ascertain the quantity of muriatic acid. (61).