Medicinal WATERS are generally impregnated with iron dissolved in the aerial acid or fixed air, with vitriol, sulphur, bitumen, &c. in consequence of which they produce various effects on the human body. The following directions for analysing them are given by Dr Lettsom.
"As many springs contain a volatile principle soon liable to be dissipated, it is necessary to make our experiments on the spot, in order to discover the contents of such waters. Various as these contents may at first appear, the apparatus proper to detect all of them may be reduced into a very small compass.
"When we propose to examine any medicinal spring, the soil and face of the country should be considered, the stony or mineral appearance, and particularly whether there are any mineral veins; the degree of heat of the water should be ascertained by a thermometer, and its comparative weight to other springs in the neighbourhood also carefully observed; after which we may enter on our experiments.
"I. Aerial Matters. 1. Mephitic, fixable, or fixed air, is heavier than common or vital air, and frequently mixed with water; by which union common water is capable of dissolving iron, and thereby forming a chalybeate spring, as in Pyrmont, Spa, and many other celebrated mineral waters.
"This mephitic air is detected by lime-water; the former precipitating the calcareous earth of the latter in a white powder. To discover the quantity of this aerial matter, a bottle filled with the mineral water should be tied over the mouth with a loose bladder: the bottle is then to be placed in boiling water, the heat whereof will extricate the mephitic air, which rising into the bladder, may be collected by tying the bladder close to the neck of the bottle, and afterwards measured by a proportionable bulk of water.
"II. Saline Bodies. 1. An acid is sometimes found in the composition of mineral waters, which is always the vitriolic.
"a. In its fixed state, which is supposed to be separated from pyrites: this is however very rare, and probably never occurs, as it cannot remain long in this state without being neutralised by earths, salts, or metals.—Many of those springs called acidula, received this name from the mephitic air we have already mentioned. If this acid be present, it may be discovered by an infusion of syrup of violets, or by an infusion of lacmus, or archil, which are turned of a brighter or reddish colour by it. This acid may be detected also by a solution of lead in the nitrous acid; the solution should be fully saturated. The nitrous acid uniting with calcareous earth, or fossil alkali, falls in a white sediment,
Water. sediment, while the vitriolic acid combines with the lead. Water.
" b. In its volatile sulphureous state.
" 2. An alkali is also very seldom found in water in its proper state.
" When a fossil alkali is present, it is more nicely detected by the syrup of violets, or infusion of lacmus, than the former, these being turned green by the least portion of alkali. If a considerable quantity of alkali were combined with the water, it might be precipitated by a solution of calcareous earth, or by acids.
" A volatile alkali may be distinguished by a solution of corrosive sublimate mercury in water, or in the nitrous acid, the alkali rendering the solution white, a precipitation of a white powder ensues: but no change is produced when the alkali is the fixed or fossil; or if any, the mercury will be precipitated in an orange, brown, or reddish powder; where there is a considerable quantity of the volatile alkali, the water turns blue by the addition of copper. When this alkali is in a very small proportion, some of the water should be distilled over.
" 3. Neutral salts are frequently found in medicinal waters.
" Glauber's salt, compounded of vitriolic acid, and fixed fossil alkali; spirit of wine added to a solution of this salt precipitates it in a white powder; but no change is produced by the addition of any alkaline salt.
" Epsom salt, formed of the same acid, and the earth of magnesia, is often a composition in purging waters. Any alkaline salt, either fixed or volatile, turns this water milky or curdly; the alkaline salt uniting with the vitriolic acid precipitates the earth of magnesia.
" Nitre is composed of the nitrous acid and fixed alkali. Water containing this salt should be evaporated, and the nitre remaining may be known by deflagration, or by its making a crackling noise over the fire. When the nitrous acid is combined with calcareous earth instead of the fixed alkali, the earth may be precipitated by the addition of this alkali.
" Common salt, consisting of the muriatic acid, and fossil alkaline salt. The acid of this salt is nicely detected by a solution of silver in the nitrous acid; the muriatic acid having a nearer affinity with silver than the nitrous, unites with the silver, which falls down in a white sediment, while the nitrous acid joins with the alkali of the common salt. It is proper to have a redundancy of the nitrous acid in the solution of silver, lest the silver be precipitated by a calcareous earth which may be in the water.
" III. Earthy Substances. CALCAREOUS earth, or calcined lime-stone, is found in moist wells and medicinal springs; the presence of which is best discovered by a solution of lead in the nitrous acid. This acid should be saturated with as much lead as it will dissolve, lest the superfluous acid should saturate the earth and prevent the precipitation of the lead. If there be any calcareous earth in the water, this solution turns it milky, and after some time a white powder is deposited, the calcareous earth precipitating the lead, by uniting with the nitrous acid.
" If calcareous earth be suspended in water by combination with the vitriolic acid, gypsum or selenites is formed, which may be discovered by the addition of
alkaline salt to this compound; the mixture should be warmed a little, to promote the precipitation of the selenitic earth.
" The same acid united with argillaceous earth, or earth of alum, produces an aluminous austere composition; and the earth may be precipitated also by alkaline salt, which uniting with the vitriolic acid, allows the earth to fall down in a sediment.
" IV. Sulphureous. SULPHUR may be suspended in its proper form, tho' it is not soluble in this state: but when the principle of inflammability in sulphur is combined with calcareous earth, or any alkali, in the form of an hepatic sulphur, it readily dissolves; in which case the water smells disagreeably, like the scourings of a gun, or putrid eggs. It is distinguished also by a solution of saccharum saturni (sugar of lead) in the nitrous or vegetable acids: a little of this solution being marked in lines on paper, and the paper suspended over the water, the volatile sulphureous fumes arising from the water turn these lines of a brown or dark colour; the inflammable matter of the sulphur uniting with the lead in the solution of the saccharum saturni, partly revives the metal, and hence produces that dark colour.
" V. Bituminous Bodies. BITUMEN frequently runs from amongst rocks, whence it is called petroleum; it is also common in the bowels of the earth, as hath been often fatally experienced from those bituminous vapours called fire-damps, which prove inflammable, and therefore differ from mephitic air, the latter extinguishing fire. Whether this inflammable vapour is formed of the principle of inflammability of sulphur and the vitriolic acid in a volatile state, is not so well ascertained as the remarkable effects produced by these bituminous bodies in the mountains of Ætna, Vesuvius, and many others mentioned in history.
" Liquid bitumen, naphtha, or petroleum, is never found combined with water, but floats on its surface in a manner evident to the eye, and may be particularly distinguished by the taste and smell.
" VI. Metallic Substances. IRON is a common ingredient in mineral waters, whence they are called chalybeate. The general method of distinguishing this metal is by an infusion of powder of galls, which turns water containing iron of a purple or black colour, deeper in proportion to the quantity of iron present.
" But the most accurate method is by means of the Prussian alkali fully saturated with the inflammable matter of dried blood. This alkali mixed with a chalybeate water turns the latter immediately blue, and deposits the iron in a powder of the same colour.
" Copper in water is precipitated in a red powder by the same alkali.
" Zinc is precipitated in a white powder by the Prussian alkali. Although this alkali precipitates all the metallic substances from acids, so that they may be distinguished from one another, it does not any of the earths.
" Arsenic has been suspected in some mineral springs, but I am acquainted with no proof of it. However, it may possibly happen that water running through arsenical veins may carry off a quantity of arsenic. To discover this, the water should be evaporated, and the residuum may be placed on a hot bar of iron; and if there be any arsenic, it is known by emitting
emitting a strong garlic-like smell: or this residuum may be moistened with oil, and put between two bright plates of copper; which, when heated, are turned of a white colour if any arsenic be present: but the smell generally affords a sufficient test."