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time of twenty-four hours, in a vessel accurately closed; after which the mixture being filtered, and the precipitate dried and weighed, the operator may proceed to examine it by the known methods. In this manner the nature of the substance will be clearly ascertained, on which the re-agent has acted, and the cause of the decomposition may consequently be inferred. A certain order may be followed in these operations, by mixing the waters first with such substances as stand least capable of altering them, and afterwards passing to other substances capable of producing changes more varied and difficult to explain. The following method is that which Fourcroy commonly uses in this kind of analysis. After having examined the taste, the colour, the weight, and all the other physical properties of a mineral water, he pours four pounds of lime water on an equal quantity of the fluid; if no precipitate is made in twenty-four hours, he is sure that the water contains neither disengaged carbonic acid nor alkaline carbonat, nor earthy salts with the base of aluminous earth or magnesia, nor metallic salts. But if a precipitate be formed, he filters the mixture, and examines the chemical properties of the deposited substance; if it has no taste, if it be insoluble in water, or effervesces with acids, or forms an insipid and almost insoluble salt by the addition of sulphuric acid, he concludes that it is chalk, and that the lime water has acted only on the carbonic acid dissolved in the water. If, on the contrary, it is small in quantity, and subsides very slowly; if it do not effervesce, and affords with the sulphuric acid a styptic salt, or a bitter and very soluble salt, it is formed by magnesia or aluminous earth, and often by both.

After the examination by lime water, Fourcroy pours on four other pounds of the same mineral water, a drachm or two of ammoniac perfectly caustic, or causes ammoniacal gass, disengaged by heat from the alkali, to pass into the water. When the water is saturated, it is left at rest in a close vessel for twenty-four hours; if a precipitate be afforded, it can only consist of ferruginous, or magnesian, or aluminous salts, whose nature is examined by the different methods mentioned in the fore

going paragraph. But the action of ammoniacal gass being more fallacious than that of lime water, which produces the same decompositions, it must be observed that this last should only be used as an assistant means, which does not afford results equally accurate with those produced by the former te-agent.

When salts with base of aluminous earth, or magnesia, have been discovered by lime water, or by ammoniacal gass, the caustic fixed alkalis may be used, to distinguish those with base of lime, such as sulphat and muriat of lime. For this purpose Fourcroy precipitates some pounds of the water, which is examined by either of these liquid alkalis, till it no longer produces any turbidness. As this alkali decomposes salts with base of aluminous earth, as well as those composed of lime; if the precipitate resembles in its form, colour, and quantity, that which lime water has afforded, it may be presumed that the water does not contain calcareous salt, and the chemical examinations of

the precipitate usually confirms this suspicion: but if the mixture is much more turbid than that made with lime water; if the deposition be much heavier, more abundant, and more readily afforded, the lime is mixed with magnesia or alumine. This is ascertained by treating the precipitate after the different methods before explained. It may easily be concluded, that iron precipitated by re-agents, at VOL. VIII.

the same time as the salino-terrestrial substances is easily known by its colour and its taste; and that the small quantity of this metal separated in these processes, is not sufficient to affect the results.

It were useless to explain at large the effects of sulphuric acid, nitrous acid, gall-nuts, r of the calcareous and alkaline prussiats, employed as reagents on mineral waters. The general account of these effects which has already been given may suffice; it need therefore only be noticed, that when they are mixed in large doses with these waters, and the precipitates collected, the nature and quantity of their principles may be more accurately ascertained, as has been done by Messrs. Bergman and Gioanetti. The products which the nitric solutions of silver or mercury afford when mixed with mineral waters deserve particular attention. It is more particularly necessary to operate with large quantities of water, when these reagents are used, in order to determine the nature of the acids contained in the waters. The analy sis of these fluids will be complete when their acids are known, because these are often combined with the bases exhibited by the re-agents before-mentioned. The colour, the form, and the abundance of the precipitates afforded by the nitric solutions of mercury and silver, have hitherto exhibited to chemists the nature of the acids which caused them. A thick and ponderous deposition immediately formed by these solutions, denotes the muriatic acid: if it is small in quantity, white, and crystallized with the nitrat of silver, or yellowish, and yellow and irregular when formed with that of mercury, and if it subside but slowly, it is at tributed to the sulphuric acid. But as these two acids are often met with in the same water, and as alkali and chalk likewise decompose the solu tions, the results or deductions made from the physical properties of the precipitates must be uncertain. It is therefore necessary to examine them more effectually: for this purpose, solutions of silver or of mercury may be mixed with five or six pounds of the water intended to be analysed. The mixtures being filtered, twenty-four hours after the precipitates must be dried, and treated according to the methods of chemistry. If the precipitate afforded by the nitric solution of mercury be heated in a retort, the portion of metal united with the muriatic acid of the waters will be volatilized into mercurius dulcis, and that which is com bined with the sulphuric acid will remain at the bot→ tom of the vessel, and exhibit a reddish colour. These two salts may likewise be distinguished by putting them on a hot coal; the sulphat of mercury, if present, emits a sulphureous acid, and aswhite, and is volatilized without exhibiting any sumes a red colour; the mercurial muriat remains smell of sulphur. These phænomena likewise serve to distinguish the precipitates which may be formed by the alkaline substances contained in smell, and are not vo'atile without decomposition. water, since the latter do not emit the sulphurcous

The precipitates produced by the combination of mineral waters with the nitric solution of silver may be as easily examined as the foregoing Sulphat of silver being more soluble than the musuccessfully used to separate these salts. Muriat riat of the same metal, distilled water may be of silver is known by its fixity, its fusibility, and especially in its being less easily decomposed than sulphat of silver. This last, placed on hot coals, silver, which may be fused without addition. emits a sulphureous smell, and leaves an oxyd of

The Leam nation of the Minera Waters by Distil

D

lation-Distillation is used in the analysis of waters, to ascertain the gaseous substances they may be united to. These substances are either air, more or less pure, or carbonic acid, or sulphurated hydrogen gass. To ascertain their nature and quantity, some pounds of the mineral water must be poured into a retort, sufficiently large to contain it, without being filled more than half or two-thirds of its capacity; to this vessel a recuryed tube is to be adapted, which passes beneath an inverted vessel filled with mercury. In this disposition of the apparatus, the retort must be heated till the water perfectly boils, or till no more elastic fluid passes over. When the operation is finished, the quantity of air contained in the empty space of the retort must be subtracted from the bulk of the gass obtained; the rest consists of aeriform fluid, which was contained in the mineral water, whose properties may quickly be known by the proofs of a lighted taper, tincture of turnsole, and lime water; if it catches fire, and has a fœtid smell, it is sulphurated hydrogen gass; if it extinguishes the taper, reddens turnsole, and precipitates lime water, it is the carbonic acid; lastly, if it maintains combustion without taking fire, is without smell, and alters neither turnsole nor lime water, it is atmospheric air. It may happen that this fluid may be purer than the air of the atmosphere: in this case its degrees of purity may be judged by the manner in which it maintains combustion, or by mixing it with nitrous or hydrogen gass, in the eudiometers of Fontana and Volta. The process used in obtaining gase ous matters contained in waters is entirely modern. A moistened bladder was formerly used, which was adapted to the neck of a bottle filled with mineral water: the fluid was agitated, and by the swelling of the bladder, an estimate was made of the quantity of gass contained in the water. This method is now known to be fallacious, because water cannot give out all its gass but by ebullition, and because the sides of the moistened bladder alter and decompose the elastic fluid obtained. It is scarcely necessary to remark, that the phenomena exhibited by the water, during the escape of the gass, must be carefully examined, and that a less quantity of water may be exposed to distillation, in proportion as its taste and sparkling indicate that it contains a larger quantity of gass.

Such is the method recommended by modern chemists to obtain the elastic fluids combined with waters: it must be observed, 1. That this process cannot be depended on, with regard to acidulous waters, unless the pressure of the atmosphere, and the state of compression of the elastic fluid under the glass vessels, be more accurately accounted for: and as this is not easily done, the absorption of carbonic acid by lime water, proposed by Gioanetti, appears to be preferable. 2. Though it has been recommended by Bergman to obtain sulphurated hydrogen gass from sulphureous waters, it does not answer, because the heat of ebulition decomposes the gass, and it is likewise decomposed by the mercury, which is converted into ethiops, as soon as it comes in contact with this elastic fluid: for this reason, litharge should be used to absorb this gass in the cold, and to deprive sulphureous waters of their sulphur.

Examination of Mineral Waters by Evaporation. Evaporation is generally considered as the most certain method of obtaining all the principles of mi. neral waters. We have before observed, and here repeat, that the experiments of Venel and Cornette

show, that long continued ebullition may deco pose saline matters dissolved in water, and that reason we have advised the examination them by re-agents, employed in greater prop tions; yet evaporation may afford much infor ation, when used, together with the analysis re-agents, which ought always to be considered one of the principal methods of examining ›

ters.

The intention of evaporation being to coll the fixed principles contained in a mineral wa it is obvious, that in order to know the nature: proportion of these principles, a considera quantity of the water must be evaporated, and much the more, in proportion as the princip appear to exist in smaller quantities. When water is thought to contain a large quantity saline matter, about twenty pounds must be e porated: if, on the contrary, it appears to but a very small quantity in solution, it wil necessary to evaporate a much larger quant It is sometimes requisite to perform this opera with several hundred pounds. The nature form of the vessels in which waters are expo for evaporation, is not a matter of indifferer those of metal, excepting silver, are altered, water; vessels of glass, of a certain magnitude, very subject to be broken; but those of gla smooth pottery are the most convenient, tho the cracks in the glaze sometimes cause an sorption of saline matter; vessels of ung ed porcelain, called biscuit, would doubt be the most convenient, but their price i considerable obstacle. Chemists have prop different methods of evaporating mineral wat some have directed distillation to dryness, in c. vessels, in order to prevent foreign substan which float in the atmosphere, from mixing w the residue; but this method is excessively te ous others have advised evaporation by a ger heat, never carried to ebullition, because they s posed that this last heat alters the fixed princip and carries a portion of them. This was the c nion of Venel and Bergman. Monnet, on the c trary, directs the water to be boiled, because motion prevents the reception of foreign mat contained in the atmosphere. Bergman ave this inconvenience, by directing the vessel to covered, and a hole left in the middle of the co for the vapours to pass out: this last met greatly retards the evaporation, because it di nishes the surface of the fluid. At the commer ment, the heat used must be sufficient to repel dust; but the greatest difference in the manipu tion of this experiment consists in some wri directing that the substances deposited should separated, as the evaporation proceeds, in or to obtain each pure and by itself; others, on contrary, direct the operation to be carried on dryness. We are of the opinion of Bergman, t this last method is the most expeditious and c tain; because, notwithstanding the care wh may be taken, in the first method, to separate different substances which are deposited or cr tallized, they are never obtained pure, and m always be examined by a subsequent analys and the method is besides inaccurate, on acco of the frequent filtrations, and the loss it occasio Lastly, it is very embarrassing, and renders evaporation much longer. Mineral waters m therefore be evaporated to dryness, in open gl vessels, on the water-bath, or still more adva tageously in glass retorts, on a sand-bath.

Various phænomena are observed during this Operation; if the water be acidulous, it emits bubbles, as soon as the heat first begins to act; in proportion as the carbonic acid is disengaged, a pellicle is formed, with a deposition of calcareous earth, and carbonat of iron. These first pellicles are succeeded by the crystallization of sulphat of lime; and lastly, the muriats of potash and soda crystallize in tubes at the surface, but the deliquescent are not obtained but by evaporation to dryness.

The residue must then be weighed, and put into a small phial, with three or four times its weight of alkohol: the whole being agitated, and suffered to subside for some hours, must be filtrated, and the alkohol preserved separate. The residue on which the spirit has not acted must be dried in a gentle beat, or in the open air; when perfectly dry it must be weighed, and the loss of weight will show what quantity of calcareous or magnesian muriat was contained, because these salts are very soluble in alkohol. We shall presently speak of the method of ascertaining the presence of these two salts in the spirituous fluid.

The residue, after treatment with alkohol, and drying, must be agitated with eight times its weight of cold distilled water, and filtered. After some hours standing, the residue is to be dried a second time, and boiled half an hour in four or five hundred times its weight of distilled water; this last residue, after filtration, consists of that which cold or boiling water is insufficient to dissolve. The first water contains neutral salts, such as sulphat of soda, or of magnesia; the muriat of soda, or potash and the fixed alkalis, especially soda united with carbonic acid: the large quantity of boiling water scarcely contains any substance but sulphat of lime. There are therefore four substances to be examined, after these different operations on the matter obtained by evaporatoa. 1. The residue insoluble in alkohol, and in water of different temperatures. 2. The salts dissolved in alkohol. 3. The salts dissolved in cold water. 4, and lastly, Those dissolved in boiling water. We shall now proceed to the experiments necessary to ascertain the nature of these different substances.

1. The residue which has resisted the action of the alkohol and water may be composed of calcareous earth, of carbonat of magnesia and iron, of atomine, and of quartz. These two last substances are seldom found in waters, but the three first are very common; the brown, or more or less deep yellow colour, indicates the presence of iron. If the residue be of a white grey, it does not contain this metal. When iron is present, Bergman directs it to be moistened, and exposed to the air til it rusts; in which state vinegar does not act on it. In order to explain the methods of separating these different substances, we will suppose an insoluble residue to consist of the five substances here mentioned; it must first be moistened, and exposed to the rays of the sun; and when the iron is perfectly rusted, the residue must be digested in distilled vinegar. This acid dissolves the lime and magnesia, and by evaporation affords the calcareous acetit, distinguishable from the acetit of magnesia, by its not attracting the humidity of the air. They may consequently be separated by deliquescence, or by pouring sulphuric acid into their solution. The latter forms sulphat of lime, which precipitates; but if the magnesian acetit be present, the sulphat of magnesia, composed of mags

nesia united with the sulphuric acid, will remain in solution, and may be contained by a well conducted evaporation. To ascertain the quantity of magnesia and calcareous earths contained in this residue, suiphat of lime is first to be precipitated: and the sulphat of magnesia, formed by the sulphuric acid poured into the acetous solution, nust then be precipitated by carbonat of potash. The quantities of these precipitates are known by weighing. When the chalk and magnesia of the residue are thus separated, the iron, the alumine, and the quartz remain. The iron and the alumine are dissolved by pure muriatic acid, from which the former is precipitated from prussiat of lime, and the latter by carbonat of potash. Thes - precipitates must likewise be weighed. The matter which remains after the separation of the alumine and iron is usually quartorse; its quantity may be known by weighing, and its habitudes by fusion of the blow-pipe with carbonat of soda. Such are the most accurate processes, recommended by Bergman, for examining the insoluble residue of

waters.

2. The alkohol used in washing the solid residue of mineral waters must be evaporated to dryness. Bergman advises treating it with sulphuric acid diluted with water, in the same manner as the acetous solution before spoken of; but it must be observed, that this process serves only to exhibit the bases of these salts. To determine the acid, which is ordinarily united with magnesia or lime, and sometimes with both, a few drops of concentrated sulphuric acid must be poured on, which excites au effervescence, and disengages the muriatic gass, known by its smell and white vapour, when the salt under examination contains that acid. This may likewise be known by dissolving the whole residue in water, and adding a few drops of the nitric solution of silver. The nature of the base, which, as we have observed, is either lime, magnesia, or both together, is known by the name of the sulphuric acid, by a similar process with that alreacy explained respect. ing the acetous solution.

3. The water used in washing the first residue of the mineral water, performed as before directed, with eight times its weight of cold distilled water, contains neutral alkaline salts, such as sulphat of soda, muriats, or marine salts, carbonat of potash, and of soda, and sulphat of magnesia: a small quantity of sulphat of iron is sometimes found. These salts never exist altogether in waters: the sulphat of soda, and the carbonat of potash, are very seldom found; but marine salt is frequently met with, together with carbonat of soda. The sulphat of magnesia is likewise frequently met with, and some waters even contain it in considerable quantities. When the first washing of the residue of a mineral water contains only one kind of neutral salt, it may easily be obtained by crystallization, and its nature ascertained from its form, taste, and the action of fire, as well as that of the re-agents: but this case is very rare, for it is much more usual to find many salts united in this lixivium. They must therefore be separated, if practicable, by slow evaporation; but as this method does not always perfectly succeed, however carefully this evaporation be conducted, it will be necessary to re-examine the salts obtained at the different periods of the evaporation. Carbonat of soda is usually deposited confusedly with the muriatic salts, but they may be separated by a process, pointed out by M. Gioanetti,

It consists in washing this mixed salt with distilled vinegar; for this acid dissolves the carbonat of soda. The mixture must then be dried, and washed a second time with alkohol, which takes up the acetit of soda, without acting on marine salt. The spirituous solution being evaporated to dryness, and the residue calcined, the vinegar becomes decomposed and burns. Soda alone remains, whose quantity may be then accurately determined.

4. The water used in the quantity of four or five hundred times the weight of the residuum of the mineral water contains only sulphat of lime. This may be ascertained by pure caustic ammoniac, which ocasions no change, while caustic potash precipitates it abundantly. By evaporation to dryness, the quantity of earthy salt contained in the water may be accurately ascertained. Artificial Mineral Waters.-The numerous processes we have prescribed for examining the residues of mineral waters by evaporation serve to ascertain, with the greatest precision, all the several matters held in solution in these fluids. Another process remains to be made to prove the success of the analysis, viz. That of imitating nature in the way of synthesis, by dissolving in pure water the different substances obtained by the analysis of mineral water which has been examined. If the artificial mineral water has the same taste, the same weight, and exhibits the same phænomena with re-agents as the natural mineral water, it is the most complete, and the most certain proof that the analysis has been well made. This artificial combination has likewise the advantage of being procured in all places at pleasure, and at a trifling expence; and is even in some cases superior to the natural mineral waters, for their whole properties may be changed by carriage, and other circumstances. The most celebrated chemists are of opinion, that it is possible to imitate mineral waters. Macquer has observed, that since the discovery of the carbonic acid, and the property it is found to possess of

rendering many substances soluble in water, it is much more easy to prepare artificial mineral waters. Bergman has described the method of composing waters which perfectly imitate that of Spa, Sheltzer, Pyrmont, &c. He likewise informs us, that they are used with great success in Sweden, and that he himself has experienced their good effects. Duchanoy has published a work, in which he has given a number of processes for imitating all the mineral waters usually employed in medicine. We may therefore hope, that chemistry may render the most essential service to the art of healing, by affording valuable medicines, whose activity may be increased or diminished at pleasure.

In order to present the reader, under one point of view, with the most conspicuous features in the composition of the mineral waters of this and some other countries, the following synoptical table is subjoined, from Dr. Saunders' work on this subject.

The reader will please to observe, that under the head of Neutral Purging Salts are included the sulphats of soda and magnesia, and the muriats of lime, soda, and magnesia. The power which the earthy muriats may possess of acting on the intestinal canal is not quite ascertained, but from their great solubility, and from analogy with salts, with similar component parts, we may conclude that this forms a principal part of their operation.

The reader will likewise observe, that where the spaces are left blank, it signifies that we are ignorant whether any of the substance at the head of the column is contained in the water; that the word none implies a certainty of the absence of that substance; and the term uncertain means that the substance is contained, but that the quantity is not known.

For the several mineral waters, consult their respective heads, as MALVERN, MOFFAT, SPA WATERS, &c.

[graphic]

4 SYNOPTICAL TABLE, sheaving the Composition of MINERAL WATERS.

Contained in an English wine pint of 28.875 cubic inches.

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* That is, 2.94 contained in the sulphat of iron, (this salt when crystallized containing 28 per cent. of oxyd of iron, according to Kirwan) and 1.875 additional of oxyd of iron.

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