If aerial acid be the means of the solution of the earth, it will separate in boiling; but more certainly by acetite of lead. The metal is precipitated, and the earth suspended by the acetous acid. As the lead would also be precipitated by a sulphat, a little more acid should be added, which will redissolve the lead if an earth has occasioned the separation. The nature of the saline neutrals can only be with certainty ascertained by evaporation and the form of their crystals. If nitre be contained in water, after a considerable evaporation, the smell of the acid may be detected on the addition of some sulphuric acid.

As copper can be discovered by the taste, we need only notice the means of distinguishing iron; though this also shows strong marks of its presence by the ochery depositions on the banks of its streams and the astringency of its taste. A ready and convenient test is, however, the calcareous prussiat, prepared by boiling lime water a little while on Prussian blue: it must be kept in well stopped phials from the light. The tincture and infusion of galls are equally useful; but a little alkali must be previously added, as an excess of acid, should there be such, will prevent the change of colour. Mr. Kirwan, in his excellent treatise on mi-"neral waters, has added a list of ' associated,' and another of 'incompatible' salts, chiefly, he remarks, for the assistance of geologists. We think a short abstract of this part of his work will be equally useful to the medical chemist. Aerated lime and selenite most frequently accompany each other; and aerated magnesia is always accompanied with aerated lime, but not vice versa. Aerated soda is generally accompanied with Glauber and common salt, but not vice versa. Epsom salt is commonly accompanied by Glauber or selenite, or both, but not vice versa. Vitriol of alum and iron are commonly associated. Common salt, unless with soda, is always attended with selenite; and the latter, very generally diffused-, accompanies all salts except soda when in any remarkable proportion Muriated magnesia is most commonly found with sea salt, but not vice versa, often with Epsom salt. Muriated lime is almost always accompanied with common salt. Ep-som and common salt decompose each otherwhen some degrees below the freezing point, producing Glauber and muriated magnesia; but in a higher temperature they react on each other.

Many salts found in mineral waters are incompatible, capable of decomposing each other; or, if simple, of decomposing some of the compound salts. This however appears to be prevented by the large proportion of the menstruum.

Aerated alkalis are incompatible with earthy or metallic salts; uncombined vitriolic acid with earthy nitrats, or muriats, or aerated earths; alkaline sulphats with earthy nitrats or muriats; Glauber with sylvian; vitriolated tartar with nitrated soda; vitriolated ammonia with nitre and sylvian; Epsom salt with nitrated or muriated lime; alum with nitrated or muriated lime, or magnesia; nitrated lime with sylvian, sal ammoniac, muriated barytes, or magnesia; nitrated magnesia with sylvian and muriated barytes; muriated magnesia with nitrated soda and lime.

From these few hints the nature of any mineral water may be ascertained with sufficient accuracy, and we shall now proceed with some account of the impregnations of mineral waters, and their medicinal powers. In this place it is unnecessary to be minute in giving the contents of each; it is the object of the chemist, rather than the physician. In a medical view we shall class the most noted mineral waters under their proper heads, and then consider the virtues of each class.

I. Waters with very inconsiderable or no impregnation.

Cold. Malvern; Holywell; Plombieres. Warm. Bristol; Matlock; Buxton.

II. Aerial, acidulous, sparkling.

1. United with alkali: Seltzer; Clifton and Tilbury in England; Carolina in Bohemia; Mont d'or and Bourbon Larchambault in France.

2. United with steel: Tunbridge, Spa, Pyrmont.

Boussan, and Pougue in France.

3. -----------------Steel, hot: Bath.

4. -----------------Steel and salts: Cheltenham and

Scarborough.

5.--------------------------------------------Hot: Vichy.

Carlsbad.

III

Saline, simply with one or more neutral salts.

Sea-water; Sedlitz and Seidschutz in Bohemia; Epsom; Balaruc and Bagnere in France.

IV. Sulphureous.

1. Cold: Harrowgate; Moffat.

2. Hot: Aix; Borset; Bareges and Dax in

France; Baden in Germany. V. Bituminous: Driburg, and some of the springs ok.

Pyrmont. VI. Metallic.

1. Vitriolated chalybeate: Hartfel. It forms a problem of no little difficulty to explain, why waters with impregnations so slight and inconsiderable should ever have become famous as medicinal. It has furnished arguments for the sceptic, and refined considerations for the pathologist. If water so pure be ever useful, might we not attribute the whole to the element alone ? and, having obtained this ' vantage ground,' may we not suppose that all the advantages of mineral waters are derived from dilution, added to changes of air and scene, absence from the distractions of business, or what would revive the recollection of distressing scenes or events ? The argument has been drawn out with much care, decked with delusive colourings, and supported by facts, which might at least occasion hesitation. Those who have indulged in excess of every kind, in indulgences the most exhausting, would certainly be benefited by a water diet, accompanied with regular hours, with exercise in free air, with tranquillity and cheerful conversation: men, whose midnight hours have been irritated by study and anxiety, would find the surest balm in calm repose; those who have never sought rest, but in fevers from wine, and 'rude wasseling,' must feel peculiar comfort in the calm of temperance and cheerfulness: men who have burnt under the torrid zone, and whose fluids are highly animalized by scorching heat, will find the cooling streams soothing and salutary. These representations may be allowed, yet they will not prove all that they are designed to show. Crowds of hectic patients seek, and often seek in vain, relief in the pure springs of Bristol; yet, had they not been advantageous, crowds would never have resorted to them. Pathology steps in to our aid, and attempts to show that medicines in a form highly attenuated may produce effects to which in a grosser state they were unequal; that the peculiar appropriate effects of every medicine are attained only in a suitable dose; and that, beyond this, each is indiscriminately stimulant. To reasonings of this kind, on either side, we need no reply; but we must have recourse to experience, which tells us. in language not to be misunderstood, that waters of a given class are highly efficacious in their appropriate diseases, let the immediate cause be what it may. If we were to give our own opinion, it would be limited and discriminated. We see striking effects of acidulous, of sulphurated, of saline, and chalybeate waters; but for this reason, must we deny them to the purer kinds ? We know that the effects we perceive are not in proportion to the doses of the active ingredient swallowed; may we not then suppose, that ingredients apparently less active may have effect in the same form? In reality, we would not give them all the merit assigned, or deny wholly their powers. We believe the purest waters have been useful; and are convinced that those which possess the more active ingredients, have been highly salutary.