MINERAL Waters

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 selenetic, when tried by the chemical proofs, show no marks of an acid or of an alkali, nor of any volatile, sulphureous, or metallic matters. Waters which contain a diseased 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 circumstances we may know, that any water which produces these effects is a hard, earthy, or selenetic 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 selenetic 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 those 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

Mineral. 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 spirit of the 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 shaken, 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 to 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 practiced, 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 which have hitherto been met with in mineral waters are,

1. Vitriolic acid. This acid is sometimes found pure and unmixed with any other substance, though more frequently joined with iron or copper. In its pure state, it is most frequently found in the neighbourhood of volcanoes, where, in the opinion of Dr Donald Monro, it is most probably "distilled from mines of vitriol or of pyrites-stone, decomposed by subterraneous fire." It seems, however, more probably to proceed from the decomposition of sulphur; for neither vitriol nor pyrites will at all give a pure acid. This only can be obtained from the fumes of sulphur, which we know abound in all such places. Dr Vandellius, in a book intitled De Thermis Agri Patavini, published in 1761, mentions a cave near to the town of Latera, about 30 miles from Viterbo, in Italy, where a clear acid water drops from the crevices of the rocks, and is collected by the country people in glazed earthen vessels. This has a mild agreeable taste, and is found to be a pure vitriolic acid much diluted. The cavern, however, is so filled with noxious vapours, that it cannot be entered without danger of suffocation except in winter, or when it blows a north wind. A similar native vitriolic water is mentioned by Theophilus Griffonius, near the town of Salvena. Varennius also mentions a spring in the province of Nola in Sicily, the waters of which are so sour, that the neighbouring people use it instead of vinegar. In some waste coal pits, the water tastes sour, and effervesces with alkalies; but in all these the acid is mixed with much vitriol, or other matter. Dr Monro mentions acid dews collected in the East Indies: this acid he supposes to be the vitriolic, and that it probably imparts some acidity to waters upon which the dews fall.

2. Nitrous and marine acids are never found in waters pure, though the former is frequently found combined with calcareous earth, and the latter with fossile alkali, calcareous earth, or magnesia.

3. Fixed air enters into the composition of all waters; but abounds particularly in those of the mineral kind, at least such as are cold. It imparts an agreeable acidulous taste to such water as it is mixed with, and is found by undoubted experiments to be that which gives the power and efficacy to the cold kind. It is known to be a solvent of iron, and that by its means this metal is very often suspended in waters; and Dr Dejean of Leyden, in a letter to Dr Monro in the year 1777, supposes it to be the medium by which sulphur also is dissolved. "Having been lately at Aix La Chapelle (says he), I mixed a solution of arsenic in the marine acid with some of the water of the emperor's bath, and immediately a true and genuine sulphur was precipitated to the bottom of the vessel in which the water was contained; which convinced me that the sulphur was dissolved by means of fixed air, though Sir Torbern Bergman thinks otherwise, and that the sulphur is suspended by means of phlogiston, and the matter of heat united in the waters; and he says, that if the concentrated nitrous acid be added to these waters, it feizes the phlogiston, precipitates the sulphur, and takes away the hepatic smell." If sulphur is by this medium suspended in

water, however, it must be by a natural process, with which we are entirely unacquainted; for we cannot unite sulphur and fixed air artificially. We are not informed whether there is any native mineral water impregnated only with fixed air; probably, indeed, there is not, for water thus impregnated becomes a very active solvent of calcareous and other earths, and must undoubtedly meet with something or other of this kind in passing through the ground. Many waters in Germany, particularly in the neighbourhood of the Rhine, are very much impregnated with this acid, and are esteemed otherwise pretty pure; but they have never been examined chemically to discover whether they are not impregnated also with some proportion of metallic or earthy substances.

4. Vegetable alkali was long supposed to be a production entirely artificial; but some late authors seem to think that it is a native salt as well as the vegetable alkali. M. Margraaf mentions his having got a true nitre, the basis of which is the vegetable alkali, from some waters at Berlin. M. Monnet says, that from the Pohoun spaw water he obtained eight grains of a grey-coloured alkaline salt from a residuum of twelve Paris pints of the water, which he saturated with the vitriolic acid; and on diluting, evaporating, and crystallizing, he obtained a tartarus vitriolatus, and not a Glauber's salt as he expected. Dr Hoffman affirms, that he obtained a vitriolated tartar from the Seltzer water by mere evaporation: but as this salt has neither been found in Seltzer nor any other water by other chemists, it is probable that he has been mistaken.

5. The fossil alkali is found in many waters in Hungary, Tripoli, Egypt, and other countries where that salt is found native. It is combined in Seltzer water, and other acidulous waters, with fixed air, and may be obtained from them pretty pure by simple evaporation. M. Monnet informs us, that he has obtained it in tolerable purity from the waters of Auvergne; but in most of the alkaline waters this salt was in an imperfect state, and may be called rather an embryo than a perfect salt; for it would not crystallize, and made a very imperfect neutral salt with acids. It was incapable also of decomposing the selenites, which was frequently found along with it in the same water.—Bergman makes mention of an imperfect alkaline salt; but observes, that all of that kind which he had an opportunity of examining, appeared to him to be no other than a genuine mineral alkali mixed with deliquescent salts.

In some of the mineral waters near volcanoes, this kind of alkali has been found so intimately united with phlogiston as to be capable of producing a true Prussian blue, on adding a solution of silver or of green vitriol to the water; of which an example is given by Dr Nichols Andrea, in the thermal waters of a spring in the island of Ichnia.

6. Volatile alkali has formerly been accounted an ingredient in mineral waters; but Dr Hoffman, and most of the later chemists, have denied this, as the volatile alkali is not a mineral substance. It is possible, indeed, that some waters in the neighbourhood of great quantities of putrid matter may give some tokens of volatile alkali, as was the case with Rathbone-place water, analysed by the Hon. Henry Cavendish.

7. Glauber's salt. Many mineral waters contain a portion of this salt, though the quantity is commonly very small. However, M. Boulduc, in the memoirs of the academy of sciences at Paris for 1724, makes mention of the waters of a spring in the neighbourhood of a village about three leagues from Madrid, which, by evaporation, yields a true Glauber's salt.—This salt, he says, is found in a concreted state about the sides of the spring, resembling the icicles which in winter hang from the roofs of houses. From this circumstance, it would seem that the water of the spring was very richly impregnated with the salt; and Dr Nichols Andrea speaks of a water at Sella, in Calabria, which is so strongly impregnated with this kind of salt, that he thinks it would be worth while to prepare it from thence in the way of trade. It is very probable that such waters are frequently to be met with in countries where the soil is impregnated with mineral alkali.

8. Common nitre. In some of the barren provinces of Bengal, the earth is so strongly impregnated with this salt, that the surface is covered with a nitrous crust resembling hoar-frost; and in such places the waters are strongly impregnated with it, as may naturally be supposed. In colder countries, however, this impregnation is more rare, though instances of perfect nitre being found in springs are not wanting in Europe; but no natural combination of nitrous acid with fossil alkali, or cubic nitre, has yet been met with in any part of the world.

9. Sea salt. This abounds not only in the waters of the ocean, but in great numbers of salt springs; and there are but few waters so pure as not to contain some portion of it.

10. Aerated fossile alkali. This is found in Seltzer, and other waters of that kind, but combined with such a quantity of fixed air, that the acrid taste of the alkali is entirely covered, and the water has a brisk acidulous one. By evaporating the water, however, this superfluous quantity of air is dissipated, and the alkali then appears in its more acrid state.

11. Gypsum, or selenites. This composition of the vitriolic acid and lime is extremely common in mineral waters. For a long time it was supposed to be a simple earth or stone, on account of its difficult solubility in water, requiring 700 or 800 times its own weight of water to dissolve it artificially, though Dr Rutty informs us, that the water in which it is originally dissolved will contain four or five times that proportion. There are to appearance several kinds of this substance; but whether they arise from foreign mixture, or from any difference in the calcareous earths among themselves, we know not. It is not, however, considered as a medicinal ingredient, nor indeed is the internal use of it thought to be very safe.

12. Epsum salt. Bergman and some other chemists have reduced all the calcareous purging salts in which the vitriolic acid is concerned; but Dr Monro observes, that these salts not only crystallize in various modes, but have different degrees of solubility in water.—Thus the Epsum salt, properly so called, dissolves in an equal quantity of water; while the calcareous nitrates, or purging salts from mineral waters, require from 10 to 80 times their weight to dissolve them.—This matter would require the analysis of a great number

Mineral. ber of salts obtained from mineral waters in large quantity, and has not yet been thoroughly explained. These salts, however, are seldom met with by themselves in mineral waters, but usually mixed with sea-salt, iron, earth, sulphureous matter, &c. Dr Rutty tells us, that a mineral water begins to be laxative when it contains ten grains of this salt to a pint, or 80 to a gallon.

13. Alum. This was formerly supposed to be a very common ingredient in mineral waters; but more accurate observations have shown it to be very rare, inasmuch that Dr Hoffman thinks it is not to be met with in any. Dr Layard, however, in the 56th volume of the Philosophical Transactions, gives an account of a chalybeate water at Somerham, from which he got five grains of alum out of two pounds of the water. Dr Rutty supposes that the mineral water at Ballycastle, in Ireland, contains also a portion of this salt.

14. Calcareous nitre. This is rarely found in mineral waters, though common enough in such as are simply called hard waters. Dr Monro says, that the only one containing this ingredient which he ever heard of is one mentioned by Dr Home, in his treatise on bleaching.

15. 16. Muriated calcareous earth, and muriated magnesia. Muriated calcareous earth is likewise a rare ingredient in mineral waters, though frequently mentioned by writers on this subject. Bergman informs us, that he obtained a small quantity from a spring in Ostro-Gothland; and Dr Monro got some from the water of a salt spring at Pitkeathly, near Perth, in Scotland. It is found, as well as muriated magnesia, in sea water, though the latter is much more abundant, and probably to be met with in all salt waters whatever, but is very difficult to be obtained in a crystalline form; though its presence and nature may always be ascertained, by dropping vitriolic acid into the concentrated liquor supposed to contain it, which will both precipitate the calcareous earth, and raise the marine acid in vapours. Muriated magnesia is likewise found in salt waters, and abounds in those of the ocean. It is the principal ingredient in the bitter ley remaining after the salt is extracted from sea-water, and is much more capable of being crystallized than the former.

17. Aerated calcareous earth, and aerated magnesia. Both these earths may be dissolved by means of fixed air, and frequently are so in mineral waters, as well as iron. They are likewise often found in great quantity in hard waters; nor is there probably any kind of water, unless that which is distilled, entirely void of them.—When such waters are boiled, the air evaporates, and the earth falls to the bottom, which will also be the case upon long exposure to the air. Hence originates the crust upon tea-kettles, the petrefactions upon different substances immersed in some kinds of water, &c. Hence also hard waters become soft, by running in channels for a considerable way; and to this cause we may with probability ascribe the growth of stones in rivulets.

18. Vitriolated copper. This salt is seldom found, except in waters which flow from copper mines. The water impregnated with it is emetic and purgative, and may justly be accounted poisonous rather than medicinal. On dipping clean iron into such water, the copper is instantly precipitated in its metallic state, and

the iron dissolved in its lead. Sometimes the quantity of copper is so great, that it is found advantageous to extract it in this way, as is the case in a certain stream in Ireland.

19. Vitriolated iron is found in considerable quantity in several waters both of England, Scotland, and Ireland, as well as in many countries on the continent. Some authors have imagined, that there is a kind of volatile vitriol with which waters are sometimes impregnated. An anonymous author, in a work intitled delle Terme Porretiane, published at Rome in 1768, informs us, that having fixed a glass receiver to a hole through which the vapour of the water rises from the aqueduct below, he found in it a month afterwards, as well as in the mouth of the hole, a concrete and incrustated substance, like flaccite, which by experiment proved to be a true salt of iron, with a superabundant quantity of acid. Hence he concludes, that this water, as it rises from the spring, is impregnated with a fine volatile martial vitriol, in such small proportion that it cannot be discovered in any quantity that may be analysed in retorts or stills, though it may be discovered by confining for a long time the vapour, which is naturally and constantly sublimed from the whole body of the thermal water discharged from the spring, as it passes through the aqueducts. The water of this spring is strongly sulphureous, and its heat 92 degrees of Fahrenheit.

Another kind of supposed volatile vitriol is that composed of iron, dissolved by fixed air. The notion of this being a volatile substance arose from observing that there are some waters which taste strongly chalybeate at the fountain, but, after running for a little way, loses it entirely. This, however, is founded on a mistake; for it is only one of the ingredients, viz. the fixed air, which flies off when it is combined with earth; after which the iron precipitates in a similar manner.

20. Vitriolated zinc. This has been found native in the bowels of the earth; and thence has been supposed, not without reason, to be an ingredient in mineral waters: but none have yet brought any decisive experiments on this subject, except Dr Rutty and Dr Gmelin, who both say that they have obtained a white vitriol from mineral waters which were at the same time impregnated with iron and some other ingredients.

21. Muriated manganese. Waters impregnated with this salt are mentioned both by Bergman and Scheele; but the particular properties of them are not known.

22. Arsenic has been supposed sometimes to be an ingredient in mineral waters, though no certain proofs of its existence have been brought. Poisonous springs, supposed to be impregnated with it, are mentioned by Varenus; and Dr Baldassari tells us of a small spring (near to the Aqua Sancta, in the country of Siena), the waters of which kill any animal that drinks them. He suspects this to be owing to arsenic, but was afraid to analyse the water.

23. Fossil oils. Almost all waters, even those which are accounted the most pure, contain some portion of an oily matter, though generally so small that it cannot be perceived without evaporating a large quantity of the liquid. Some contain it in great quantity; inasmuch that, besides impregnating the water as strongly as possible, a great quantity falls to the bottom,

Mineral. tom, or swims on the top. The other ingredients of these bituminous waters have not been examined; but in whatever manner the oil is united with the water, a portion of it adheres very obstinately, so that it cannot be fully separated even by filtration through paper. A fine bituminous vapour rises from the bottom of some wells, and pervades the water, taking fire on the application of any flaming substance, though no oil is observed in the water itself. Of this kind are the burning wells at Brofely and Wigan in Lancashire in England, and others in different countries. The cause of the inflammation of these waters was first discovered in 1759 by Mr Thomas Shirley, who caused the waters of the well at Wigan to be drained away; and found that the inflammable vapour rose from the ground at the bottom, where it would take fire, as it did at the surface of the water. On applying his hand to the place whence the vapour issued, he found the impulse of it like a strong breath; or wind; and the same sensation was felt on applying his hand to the surface of the water. See Phil. Trans. vol. 26.

24. Sulphur. This is a common ingredient in mineral waters; and its presence is known by the strong hepatic smell they emit, as well as by their blackening silver, &c. Sulphureous waters are frequently very clear and transparent when taken up at the fountain; but when kept in open vessels, or bottles not well stopped, they soon deposit the sulphur they contain in the form of a dirty white powder, and lose their sulphureous smell. The bottom of the wells containing such waters, or of the channels in which they run, assume a black colour, and a raggy kind of matter is deposited on such substances as they run over for some time; and when these are taken up and dried, they appear covered with a true sulphur. Some waters contain this ingredient in very considerable quantity. From that of Harrowgate it may be separated by filtration; and Father de Tertre, in the second volume of his Histoire Naturelle des Antilles, tells us, that when he was in the island of Guadeloupe, and amusing himself one day with evaporating in a tin plate some sulphureous water which he found near the burning mountain, there remained on the plate a layer of sulphur about the thickness of a leaf of paper. Dr Monro mentions his having obtained a true sulphur, by evaporation, from a mineral water at Castle-Led, in the county of Ross, in Scotland. Dr Brown, in his Travels, informs us, that having caused some of the pipes which carry off the water from the duke's bath at Baden, in Austria, to be opened, he took from thence a quantity of fine sulphur in powder, something like flour of brimstone, which had been sublimed from the waters. A similar kind of sulphur is obtained from the upper part of the pipes and conduits which convey the waters of Aix-la-Chapelle from their sources.

From these, and other facts of a similar nature, Dr Monro concludes, that sulphur is dissolved by some means or other in the water. Great differences, however, have taken place among chemists concerning the mode in which sulphur is thus dissolved. Sulphur, we know, may be dissolved by means of an alkali, as well as by calcareous earth; and there are some instances of alkaline waters containing sulphur, though we are not absolutely certain that the alkaline salt is the bond of

union betwixt the sulphur and them. Dr Vandellius, in his treatise de Thermis agri Patavini, already quoted, mentions a substance found in the conduits of the waters of the baths at Aponum, which he calls crystallized sulphur, and says that it dissolves in the waters by boiling, recovering afterwards its solid form. This substance has not been examined; but we know of no other mineral with which sulphur readily assumes a crystalline form than terra ponderosa. This compound is easily dissolved in water, and communicates to it a most powerful taste and smell of hepatic sulphur. Great part of the terra ponderosa, though not the whole, may be separated by fixed air, so that it is probably this permanent compound which Vandellius observed. Dr Lucas supposed that the sulphureous waters contain both an acid and phlogiston; and Sir Torbern Bergman, that they are impregnated only with the hepatic gas; and that this gas consists of sulphur united with phlogiston, from which the sulphur may be precipitated by the nitrous acid.

For an account of the cause of heat in mineral waters, see the article SPRINGS.

Having now mentioned the principal substances that form almost all these waters, we shall next 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 turnsol, 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, shows 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 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 turbid mineral; or by crystallization.

Common salt contained in waters forms with a solution

Mineral. lution of silver in nitrons 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 them, 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. 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 AEROLOGY, 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.

Names of
Springs.
Pyrmont,

Countries in which
they are found.
Westphalia, Germa-
ny.

Contents and Quality of the
Water.

Medical Virtues.