natural history, is used in general for all fossile bodies, whether simple or compound, dug out of a mine; from whence it takes its denomination.
Mineral Waters. All waters naturally impregnated with any heterogeneous matter which they have dissolved within the earth may be called mineral waters, in the most general and extensive meaning of that name; in which are therefore comprehended almost all those that flow within or upon the surface of the earth, for almost all these contain some earth or selenites. But waters containing only earth or selenites are not generally called mineral, but hard or crude waters.
Hard waters, which are simply selenitic, when tried by the chemical proofs, shew no marks of an acid or of an alkali, nor of any volatile, sulphureous, or metallic matters. Waters which contain a disengaged calcareous earth, change the colour of syrup of violets to a green; and those that contain selenites, being mixed with a solution of mercury in nitrous acid, form a turbith mineral; and when a fixed alkali is added, they are rendered turbid, and a white sediment is precipitated. These waters also do not dissolve soap well. From these we may know, that any water which produces these effects is a hard, earthy, or selenitic water. The waters impregnated with gas are also hard.
Although the waters of the sea and saline springs be not generally enumerated amongst mineral waters, they might nevertheless be justly considered as such: for besides earthy and selenitic matters, they also contain a large quantity of mineral salts. We shall therefore consider them as such in this article.
Mineral waters, properly so called, are those in which gas, or sulphureous, saline, or metallic substances, are discovered by chemical trials. As many of these waters are employed successfully in medicine, they are also called medicinal waters.
Mineral waters receive their peculiar principles by passing through earths containing salts, or pyritous substances that are in a state of decomposition. Some of these waters are valuable from the quantity of useful salts which they contain, particularly of common salt, great quantities of which are obtained from these waters; and others are chiefly valued for their medicinal qualities. The former kind of mineral waters is an object of manufacture, and from them is chiefly extracted that salt only which is most valuable in commerce. See Salt.
Many of these waters have been accurately analysed by able chemists and physicians. But notwithstanding these attempts, we are far from having all the certainty and knowledge that might be desired on this important subject; for this kind of analysis is perhaps the most difficult of any in chemistry.—Almost all mineral waters contain several different substances, which being united with water may form with each other numberless compounds. Frequently some of the principles of mineral waters are in so small quantity, that they can scarcely be perceived; although they may have some influence on the virtues of the water, and also on the other principles contained in the water. The chemical operations used in the analysis of mineral waters, may sometimes occasion essential changes in the substances that are to be discovered. And also, these waters are capable of suffering very considerable changes by motion, by rest, and by exposure to air.
Probably also the variations of the atmosphere, subterranean changes, some secret junction of a new spring of mineral or of pure water, lastly the exhaustion of the minerals whence waters receive their peculiar principles, are causes which may occasionally change the quality of mineral waters.
We need not therefore wonder that the results of analyses of the same mineral waters made by different chemists, whose skill and accuracy are not questioned, should be very different.
The consequences of what we have said on this subject are, That the examination of mineral waters is a very difficult task; that it ought not to be attempted but by profound and experienced chemists; that it requires frequent repetitions, and at different times; and lastly, that no fixed general rules can be given concerning these analyses.
As this matter cannot be thoroughly explained without entering into details connected with all the parts of chemistry, we shall here mention only the principal results, and the most essential rules, that have been indicated by the attempts hitherto made on this subject.
We may admit the division or arrangement of mineral waters into certain classes, proposed by some of the best chemists and naturalists.
Some of these waters are called cold, because they are not naturally hotter than the atmosphere. Some of them are even colder, especially in summer.
Those are called hot mineral waters, which in all seasons are hotter than the air. These are of various degrees of heat, and some of them are almost as hot as boiling water. In some mineral waters certain volatile, spirituous, and elastic principles may be perceived, by a very sensible piquant taste: this principle is called the gas or the spirit of waters.
The waters which contain this principle are generally lighter than pure water. They sparkle and emit bubbles, at their spring, but especially when they are shook, and poured from one vessel into another. They sometimes break the bottles containing them, when these are well corked, as fermenting wines sometimes do. When mixed with ordinary wine, they give it the piquancy and sparkling quality of Champagne wine.
This volatile principle, and all the properties of the water dependent upon it, are lost merely by exposure to air, or by agitation. The waters containing this principle are distinguished by the name of spirituous mineral waters, or acidulous waters. Other divisions of mineral waters may be made relatively to some of their predominant principles. Hence some waters are called acidulous, alkaline, martial, neutral, &c.
When a mineral water is to be examined, we may observe the following rules:
Experiments ought to be made near the spring, if possible.
The situation of the spring, the nature of the soil, and the neighbouring rising grounds, ought to be examined.
Its sensible qualities, as its smell, taste, colour, are to be observed.
Its specific gravity and heat are to be ascertained by the hydrostatical balance and the thermometer.
From the properties above-mentioned of spirituous mineral waters, we may discover whether it be one of this class. For greater certainty we may make the following trial. Let the neck of a wet bladder be tied to the neck of a bottle containing some of this water. By shaking the water, any gas that it may contain will be disengaged, and will swell the bladder. If the neck of the bladder be then tied with a string above the bottle, and be cut below this string, so as to separate the bladder from the bottle, the quantity and nature of the contained gas may be further examined.
Lastly, we must observe the changes that are spontaneously produced upon the water in close and in open vessels, and with different degrees of heat. If by these means any matter be crystallized or deposited, it must be set apart for further examination.
These preliminary experiments and observations will almost certainly indicate, more or less sensibly, something concerning the nature of the water, and will point out the method to be followed in our further inquiry.
We must then proceed to the decomposition of the water, either without addition, and merely by evaporation and distillation, or with the addition of other substances, by means of which the matters contained in the water may be precipitated and discovered. It is not material which of these two methods be first practised, but it is quite necessary that the one should succeed the other. If we begin by evaporating and distilling, these operations must be sometimes interrupted, that the several principles which rise at different times of the distillation may be obtained and examined separately, and also to allow the several salts that may be contained to crystallize by the evaporation and by cold.
The substances generally found in mineral waters, are almost always combinations of vitriolic acid, and those of marine acid, together with the several matters that these acids are capable of dissolving.
The following combinations of vitriolic acid are found in mineral waters.
1. Volatile sulphureous acid. This is seldom found, both because it easily loses its phlogiston, and because it must almost always meet with some substance that it is capable of dissolving.
2. Sulphur. This is found sometimes singly, but generally in form of a liver of sulphur. In these waters, sulphur is formed into a heap by means of calcareous earth or of mineral alkali.
3. Vitriolic salts with earthy bases. These salts are frequently selenitic, that is, their acid is combined with a calcareous earth; or they are of the nature of Epsom salt, the basis of which is magnesia. Sometimes, but not so frequently, they are aluminoir, when their acid happens to be united with an argillaceous earth.
4. Vitriols. Martial vitriol is frequently contained in mineral waters; vitriol of copper is sometimes, but seldom, and vitriol of zinc is still more rarely found in these waters. The vitriols of other metallic substances are scarcely ever, but in very singular cases, found in water.
5. Lastly, vitriolic salts with basis of fixed alkali. This is always Glauber's salt. Neither vitriolated tar nor vitriolic ammoniacal salt are ever found, unless by some singular accident, in mineral waters.
The combinations of marine acid that are contained in mineral waters are common salts, and marine salt with earthy basis. For no combinations of this acid with phlogiston are known, and it is very seldom found united with any metallic substance.
Compounds formed of the nitrous acid with an earthy basis are very common in waters in this country, insomuch that some have thought that nitre might be extracted from them advantageously in the way of trade. See Chemistry, n° 178. In France, however, the case seems to be otherwise; for Mr Macquer determines, in his Chemical Dictionary, that the nitrous acid is not (nay that it cannot) be found in waters except by accident.
These are the principal substances that form almost all these waters. We shall now show the proofs by means of which they may be discovered in water, without decomposing the water by evaporation or by distillation.
If any portion of disengaged acid or alkali be contained in water, it may be known by the taste, by changing the colour of violets or of turpentine, and by adding the precise quantity of acid or of alkali that is necessary for the saturation of the contained disengaged saline matter.
Sulphur, and liver of sulphur, may be discovered in waters by their singular smell, and by the black colour which these substances give to white metals or to their precipitates, but especially to silver.
Vitriolic salts with earthy basis may be discovered in water by two proofs: 1. By adding some fixed alkali, which decomposes all these salts, and precipitates their earthy basis; and, 2. By adding a solution of mercury in nitrous acid, which also decomposes these salts, and forms a turbid mineral with their acid. But for this purpose the solution of mercury ought to have a superabundant quantity of acid: for this solution, when perfectly saturated, forms a precipitate with any kind of water, as M. Rouelle has very justly remarked; and indeed, all metallic solutions in any acids are strictly capable of decomposition by water alone, and so much more easily as the acid is more perfectly saturated with the metal.
Martial vitriol or iron combined with any acid, or even with gas, shews itself in waters by blackening an infusion of galls, or by forming a Prussian blue with the phlogisticated alkaline lixivium.
The vitriol of copper, or copper dissolved by any acid, may be discovered by adding some of the volatile tile spirit of sal ammoniac, which produces a fine blue colour; or by the addition of clean iron, upon the surface of which the copper is precipitated in its natural or metallic state.
Glauber's salt is discovered by adding a solution of mercury in nitrous acid, and forming with it a turbith mineral; or by crystallization.
Common salt contained in waters forms with a solution of silver in nitrous acid a white precipitate, or luna cornea. It may also be known by its crystallization. Marine salt with earthy basis produces the same effect upon solution of silver. It also forms a precipitate when fixed alkali is added. The acrimony, bitterness, and deliquescency of this salt, serve to distinguish it.
The proofs related for the examination of mineral waters, are only those which are most essential. Many others may be made to confirm the former proofs; but the details of these are too extensive to be inserted here. We shall add only two of these, because they are very general, and may be very useful.
The first is the production of artificial sulphur, or of the volatile sulphureous acid; by which means the vitriolic acid may be discovered in any combination whatever. For this purpose, the matter to be examined must be mixed with any inflammable substance, and exposed to a red heat. If this matter contained but a particle of vitriolic acid, it would be rendered sensible by the sulphur, or by the volatile sulphureous acid thence produced.
The second general proof for mineral waters which we shall mention here, serves to discover any metallic substance whatever, dissolved in water by any acid. This proof consists in adding some of the liquor saturated by the colouring matter of Prussian blue, described under the article Chemistry, no 391. This liquor produces no effects upon any neutral salts with earthy or alkaline bases, but decomposes all metallic salts; so that if no precipitate be formed upon adding some of this liquor, we may be certain that the water does not contain any metallic salt; and on the contrary, if a precipitate be formed, we may certainly infer that the water does contain some metallic salt.
Two kinds only of gas, or the spirituous volatile part of some waters, are hitherto known; of which one is the volatile sulphureous acid, and the other is fixed air. See Air, Fixed Air, and Gas, passim. Air united superabundantly with spirituous waters is the chief cause of their lightness, piquancy, and sparkling.
When the nature and quantities of the principles contained in a mineral water are ascertained by suitable experiments, we may imitate artificially this water, by adding to pure water the same proportions of the same substances, as Mr Venel has done in examining several waters, especially that of Selters.
We may easily perceive the necessity of using no vessels in these experiments, but such as are perfectly clean and rinsed with distilled water; of weighing the products of the experiments very exactly; of making the experiments upon as large quantities of water as is possible, especially the evaporations, crystallizations, and distillations; and of repeating all experiments several times. We may further observe, that the mixtures from which any precipitates might be expected ought to be kept two or three days, because many of these precipitates require that time, or more, to appear, or to be entirely deposited.