To the sense of smelling, good water is free from odour. When saturated with the aerial acid, it exhales a suffocating, subtile vapour. Hepatic waters resemble in smell a stale egg, or the scourings of afoul gun; those impregnated with putrid extractive matter are distinguished by their fetor.

Waters may be considered as pure, in proportion to their want of taste: even in the purest, however, the experienced water drinker will discover a difference. The aerial acid gives an agreeable pungency. Bitterness shows an impregnation of Glauber's salt, nitre, vitriolated, nitrated, or muriated magnesia, nitrated or muriated lime. Lime and selenite are distinguished by a slight austerity; alum by a little stypticity; common salt by its saline taste; alkali by its urinous flavour; copper and iron by tastes peculiarly their own, and sufficiently known.

The quantity of foreign matter in medicinal waters is ascertained by their specific gravity, compared with that of water at the same temperature. The comparison should be made with distilled water, not in small quantities, for the difference is not easily ascertained; nor in large ones, as the greater weights are not minutely exact. Vessels which hold a quart or three pints form the proper mean. . The specific gravity is, however, only a test of the quantity of matter in waters without smell, for the hepatic waters are lighter than distilled. The water of Limmer and Rensdorf are instances of this kind, examined by Andria and Brock-man. The lightest water is that of Envie, near Turin, eight pounds of which contain about half a grain of lime: the heaviest, that of the Dead Sea, which, according to Lavoisier, contains 44.4 per cent. of common salt, muriated lime, and magnesia, so that it is evidently a salt lake, whose fluid contents are decreasing. These extremes are 1.0000 and 1.2403. If waters abound with aerial acid, their specific gravities do not give the proportion of solid matter with any accuracy at a temperature above 50°. A convenient rule, sufficiently accurate, is given by Mr. Kirwan to ascertain the solid contents by the specific gravity, which we shall transcribe. It consists in subtracting 1000 from the given specific gravity expressed in whole numbers, and multiplying the product by 1.4. This gives the weight of the salts in their most desiccated state, but that of fixed air is also included. The fixed air should of course be previously separated, and the water of crystallisation allowed for. We shall therefore add at the end a very convenient table from Kirwan, to which we shall often have occasion to refer.

Another method of estimating the medicinal from the sensible qualities of waters, is, an examination of their temperature. For this purpose, it will be of use to enquire whether the temperature is the same at all seasons, whether it follows the variations of the atmosphere, or the water freezes in winter; if warm waters deposit any sediment in cooling; of what this sediment consists; and whether their sensible qualities are diminished or destroyed after the deposition.

The situation of the waters must not be neglected. The character and elevation of the neighbouring country; the quantity of the water, and the occasional variations in this respect; its current; the number of its springs, and the quantity they furnish; the quantity and nature of their depositions; what sublimations are observable in their channels; whether they flow tranquilly or with ebullition; what vegetables and animals they support; are circumstances of real importance in ascertaining the nature of mineral waters.

It cannot form a part of our present object to engage in details of the various methods employed in the analysis of mineral waters; yet, as the medical practitioner is sometimes called on to determine on the propriety of using any water which has not been hitherto analysed, a few short rules may not be improper or misplaced; they are not designed to obtain an accurate analysis, but to form a general idea of the nature of any water offered to observation. The description of the sensible properties of the different kinds of mineral waters will lead to a general knowledge of their contents. The acidulous waters will tinge the juice of litmus red, but the colour will disappear by exposure to the air: they will also precipitate lime from lime water, which will be again dissolved if a small quantity only is added, or if the air be in excess. If a flaccid bladder be tied round the mouth of a bottle containing the water, and heat applied, the quantity of uncombined air may be measured by the quantity in the bladder.

The hydrogenated sulphur will tarnish silver, or, more readily, lead. A mark made on paper with acetite of lead or tartrite of bismuth is instantly blackened, without producing any furbidness. A sulphuret of either fixed alkali will indeed produce the same effect, but a decomposition ensues. When the sulphur is combined with the water by means of an alkali, it may be precipitated by the sulphuric or muriatic acid, and weighed; but some sulphur will still remain suspended. Either the sulphureous acid, or the strong red nitric acid, will precipitate what is left. Oxides of lead, quicksilver, and arsenic, by uniting with the hydrogen of the gas which keeps the remaining sulphur suspended, will have the same effect. By these means we can also separate the sulphur, dissolved by means of hydrogenous gas in water.

Alkalis, when uncombined or aerated only, are discovered by changing the colour of syrup of violets green. To ascertain whether this change is owing to the fixed or volatile alkali, some muriat of quicksilver must be added. The volatile attracts a large portion of the acid, and the rest is precipitated with the metal in the form of mercurius dulcis.

Acids are more easily discovered. The muriated barytes is decomposed by the sulphuric acid, forming an almost insoluble compound, and all its salts are thus at once discovered: an almost imperceptible particle of either forming a. precipitate. The muriatic acid can be as certainly discovered by a solution of nitrated silver with an excess of acid. Having ascertained the nature of the acid, if in the first instance an alkali is added, the lime, if the water contain a calcareous earth, is deposited; or argil, or magnesia, if these be its ingredients. If the precipitate be soluble in distilled vinegar, it is not argil; if, when dissolved, and sulphuric acid be added, no precipitation ensues, it is not calcareous, and consequently must be magnesia. The acid of sugar will at once show the existence of calcareous earth, for its attraction is very powerful and the compound insoluble.