The first circumstance to be attended to in the chymical examination of any mineral water, is to determine the gross weight of the substances held in solution. This is to be done by first ascertaining the specific gravity of the mineral water; then substracting from it the specific gravity of distilled water (both expressed in whole numbers), multiplying the remainder by 1.4. The product is the gross saline contents, in a quantity of the water denoted by the number employed to indicate the specific gravity of distilled water.2 Thus, if the specific gravity of the mineral water be 1.079, as that of distilled water is 1.000, the remainder, after, the subtraction of the latter from the former, in whole numbers, will be 79, which multiplied by 14 makes 1106; and, therefore, 110.6 is the sum of the saline contents of 1000 parts of the water; or 11.06 are contained in 100 parts. The next step is to ascertain the nature and the proportion of each ingredient.

1. The Aerial or Gaseous Bodies are to be first separated by boiling for a quarter of an hour as much of the water as will fill two thirds of a glass retort, connected with an inverted jar, divided into cubic inches and tenths, full of mercury, and placed in a mercurial trough. The air and gases will pass over into the jar, and depress the mercury; and when cool, after subtracting the air of the retort, the quantity of air expelled from the water may be easily determined.

The only gaseous bodies contained in water are atmospheric air, oxygen gas, nitrogen gas, carbonic acid gas, sulphuretted hydrogen gas, and sulphurous acid; of which the following cannot exist together in the same water : - Oxygen gas and sulphuretted hydrogen gas, Sulphuretted hydrogen gas and sulphurous acid.

a. Sulphuretted hydrogen gas is known to be contained in water by its peculiar odour, by the water becoming turbid when exposed to the air, and depositing sulphur, by its reddening litmus fugaciously, blackening paper dipped in a solution of lead, and precipitating nitrate of silver black or brown. It may be separated from the air obtained from water during boiling, by carrying the jar into a tub of warm water, and introducing nitric acid, which absorbs the sulphuretted hydrogen. The bulk of this gas contained in any water is determined by filling a jar three fourths with the water, inverting it in a water trough, and introducing nitrous gas at intervals, as long as red fumes appear, or the hepatic odour continues; when the jar is turned up and the air blown out. The nitrous gas in this operation mixing with the common air in the upper part of the jar forms nitrous acid, which renders the water turbid, by decomposing the sulphuretted hydrogen and precipitating sulphur. The bulk of hepatic gas is determined by the weight of the sulphur thrown down, one grain indicating the presence of 3.33 cubic inches of the gas.

b. Sulphurous acid gas is ascertained by the same tests which detect the presence of sulphuric acid and water {which see).

c. Carbonic acid gas is detected by lime-water occasioning a precipitate soluble with effervescence in hydrochloric acid; by reddening fugaciously tincture of litmus, and losing this property when boiled.

To estimate the bulk of these gases, introduce into the air obtained by boiling the water a solution of pure potassa, and agitate the whole gently. These acid gases will be absorbed, and any other gases left; after which, the bulk of the residuum must be estimated, and subtracted from the bulk of the whole to obtain that of the acid gases absorbed. Evaporate next the potassa slowly, nearly to dryness : and by leaving it exposed to the atmosphere, sulphate of potassa will be formed, which may be separated by dissolving the potassa in diluted hydrochloric acid, and filtering the solution. 100 grains of sulphate of potassa indicate 42.72 cubic inches of sulphurous acid gas, which being subtracted from the bulk of the gas absorbed by the potassa, leaves the bulk of the carbonic acid gas.

1 The following observations on this important subject are chiefly extracted from the System of Chymistry of Dr. Thompson.

2 This useful formula was invented by Mr. Kirvvan. See Essay on Mineral Waters, 145.

d. Oxygen gas, after the above gases are separated, may be examined by means of the solution of sulphate of iron saturated with nitrous gas.1 A small graduated tube filled with the air to be examined is to be plunged into this solution, and moved backwards and forwards for a few minutes. The whole of the oxygen is rapidly absorbed; and by marking the greatest absorption, its bulk in a given quantity of the air is ascertained.

e. Nitrogen gas is detected by not being affected by eudiometrical processes. 2. Alkalies, and Alkaline, Earthy, and Metallic Carbonates. Alkalies, even in minute quantities, are discovered in water by rendering infusion of turmeric, or paper stained with it, brown.2 When the change is permanent, the fixed alkalies may be supposed to be present; when fugacious, the alkali is ammonia. An infusion of Brazil-wood is rendered blue by the alkalies; but this also is the case with the alkaline and earthy carbonates 3, and the addition of sulphuric acid produces effervescence. Tincture of nutgalls discovers iron; the colour is violet if alkaline carbonates or earthy salts be also present; dark purple indicates other alkaline salts; purplish red, sulphuretted hydrogen gas; and whitish and then black, sulphate of lime. Boiling the water precipitates the earthy and metallic carbonates.

The following substances of this class, set down in the first column, are incompatible, or cannot exist in mineral waters, with the salts placed in the opposite column : -