The quantity of the saline ingredients in a mineral water may be ascertained either by finding its specific gravity, or by evaporation.
Air. Kirwan has given an easy rule, by which we can ascertain the proportion of the saline matter by the spe cific gravity of the fluid. The specific gravity of dis tilled water must be subtracted from that of the mine ral water, and the remainder must be multiplied by 1.4. The product is the quantity of saline matter, in a quantity of the mineral matter, equivalent to the num ber denoting the specific gravity of the distilled water. Thus, suppose the specific gravity of distilled water 1000, and that of the mineral water 1100, then 1100 1000 x 1.4 = 140.00 and 1000 : 140.00 : : 100 : 14.000; the fluid therefore contains 14 per cent. of saline mat ter, supposing this free of its water of crystallization.
58. The other method of ascertaining the quantity of saline matter, is to evaporate slowly by heat, a cer tain quantity of the fluid to dryness, and expose the re sidue to a temperature sufficient to drive off the whole of the water ; the residue indicates the quantity of sa line ingredients.
59. Sulphuric acid. The quantity of sulphuric acid present, is ascertained by exposing to a red heat the precipitate given by baryta, (42.) ; 100 gr. of it are equi •alent to 34 of real sulphuric acid.
60. Boracic acid. To find the quantity of boracic acid, add sulphuric acid to the precipitate given with the acetate of lead (44.) filter the fluid, and evaporate it to dryness. Dissolve the residue in alcohol, and again evaporate. The residue is boracic acid.
61. Muriatic acid. The quantity of muriatic acid is known by igniting the precipitate afforded by the salt of silver, (43.) 100 gr. are equivalent to 19 of muriatic acid.
62. Linzc. The proportion of lime is ascertained by drying by a gentle heat the precipitate thrown down by oxalic acid (48.) 100 gr. = 44 lime. Or, the precipi tate may be exposed to a high temperature, and then converted to sulphate by the addition of sulphuric acid. 100 gr. of this, after ignition, are equivalent to 41.5 lime.
63. Magnesia and alumina. By boiling in potassa the precipitate of magnesia and alumina thrown down by potassa, (56.) the magnesia will be left, and, after be ing washed and dried, must be weighed. By adding mu riatic acid to the solution of the alumina, and then sub carbonate of potassa, the earth will be precipitated. It must be washed, exposed to a red heat, and weighed.
64. Iron. Different methods are recommended for ascertaining the quantity of iron or its oxides.
Some chemists have objected to the prussiate of potassa, as an accurate method of indicating the quan tity of iron, as this salt itself contains iron, which is thrown down, and forms part of the precipitate. This
'source of error may be avoided, by ascertaining the quantity of iron that a given weight of the prussiate, carefully prepared, (53.) contains. This is done by exposing 100 grains of it to heat, in an open vessel, by which the oxide of the metal is obtained. In using this test then, to find out the quantity of iron in the mineral water, the quantity of prussiate employed must be as certained, and the weight of the oxide, which this is known to contain, must be subtracted from the weight of the precipitate. 100 grains of the blue precipitate, dried by a gentle heat, according to Porret = 34.23 per ox ide of the metal.
Another method of ascertaining the quantity of iron, is to bring the metal to a high state of oxidation, by exposing it for some time, in an open vessel, to a strong heat, in which condition it is insoluble in nitric acid. By pouring this acid on the residue, the oxide of iron is left, while the other substances are dissolved.
Of the Methods followed for ascertaining the state of Combination in which the different ingredients exist in Mineral Waters.
Very different opinions are entertained with respect to the state of combination in which the different in gredients exist in mineral waters. Some chemists sup pose that they form binary compounds; others, on the contrary, imagine, that they arc all more or less united with each other. Thus, if there be an acid, an alkali, and an earth together, it is not supposed that these are in the state of binary compounds, forming a salt of the alkali and another of the earth, but that they are com bined so as to form a triple salt. The former is the more prevalent opinion. Some chemists assert also, that the salts procured by the evaporation of the fluid are those which exist in solution, while others maintain, that during the evaporation, new compounds are formed, so that we do not by this means procure those which the water in its natural state contains. This assertion is strengthened by the fact, that some salts exist together in solution, when much diluted, which decompose each other when the solution is concentrated. During the evaporation of a mineral water, therefore, new affinities may exert their influence, and salts, different from those which exist in the water, may be obtained. The expe riments of Dr. Alunay, immediately to be stated, tend to confirm this opinion.