fixed air dissolved in it, when under the pressure which it receives whilst under ground, than when it is only under the pressure of the atmosphere. It is a higher degree of charging with fixed air, produced artificially, which causes the sparkling and effervescence of sodawater. The water in some springs in Germany, which are charged almost to the same extent, is carefully preserved in bottles, and meets with an extensive sale, as a much esteemed and wholesome beverage. The Seltzer and Fackenger waters are of this description. Besides the carbonic acid on which the sparkling appearance and briskness of the water of the most-esteemed springs depend, water, as it passes through the earth, becomes charged with other principles; which, as they are capable of complete solution, may render the water very impure, without altering its transparency. It is on the presence or absence of these admixtures that the hardness or softness of spring-water depends. These principles dissolved in spring-water, on which its hardness depends, are very various, according to the nature of the ground through which it has filtered. Sometimes it is merely carbonate of lime, which is seldom of much consequence to the health of those who drink it. The greater portion of it may be separated by boiling, which drives off the carbonic acid, and causes the earthy particles to collect at the bottom and sides of the vessel, in the form of fur. Sometimes the springwater is rendered hard by holding in solution sulphate of lime, otherwise called "selenite, or gypsum." This is not so easily separated from the water as carbonate of lime; and it seems at times to produce a disturbing effect on the stomach and bowels of those who drink it, especially when they commence the use of it. This observation is almost invariably made by those who

visit Paris, the water of which city appears to be contaminated with this salt. There are many springs whose waters are charged with earthy and metallic salts, which are much more sensible to the taste, and more disagreeable in their effects, than those which I have just mentioned. For example, some springs contain common salt; others Glauber-salt, Epsom-salt, or saltpetre, carbonate of iron, or green or blue vitriol. The first of these, though useless for drink or washing, are often of great value, in furnishing large quantities of the finest salt. The others are seldom turned to any useful purpose, except where their ingredients exist in such proportions as to render them applicable to medicine; and in this way, some of these impure springs have obtained a well-merited reputation.

The great importance of good springs of water has been felt and acknowledged from the earliest periods. Some of the most ancient settlements of the human race appear to have been determined by them. This has been particularly the case in and near the torrid zone, where the want of water is most severely felt, and where its scarcity is most likely to occur. I need only refer to the early records of sacred history, for the confirmation of this remark. In like manner, the inconvenience of bad water has been so severely felt, that it has been handed down by history, by tradition, and by the names of the places in which it occurs. Its striking influence on the murmuring Israelites at Meribah, and the signal miracle which effected their deliverance, must be familiar to every one.

RIVER-WATER, like spring-water, must be very much influenced by the nature of the country through which the water passes. As far as the principles which it has received are concerned, what I have stated

with respect to spring-waters will suffice here. There are, however, some particulars with regard to riverwater generally which must not be passed over. By the constant exposure of a large surface to the air, and also by motion, it loses most of its carbonic acid: hence, it is not only much flatter to the taste than spring-water, but it also contains less of the earthy carbonates in solution. It contains, however, more dissolved atmospheric air; and is therefore more adapted to preserve the life of fish, and other aquatic animals. Some of these are of almost microscopic size, and become one of the sources of impurity in river-water, which often holds both living and dead animal and vegetable matter in a state of suspension. Besides these matters, finely levigated, earthy particles are often suspended in river-water, and deprive it of its transparency. From any of these it may be easily separated, by rest, boiling, and filtration. River-water is at times contaminated by the reflux of the sea. When the admixture of salt-water is considerable, it is rendered wholly unfit for dietetic purposes; but when only slightly brackish, it has, for some of them, been preferred to fresh; as, for example, for the brewing of beer destined for long keeping :-this supposed superiority is, however, very doubtful

STAGNANT WATER.-This, as it exists in small lakes, pools, ditches and marshes, is, in general, very untit for purposes of diet, from the large quantity of living and decomposed animal and vegetable matter which it contains. It is also very liable to be contaminated with carburetted and sulphuretted hydrogen gases, which contribute to confer upon it an offensive odour. The pernicious effects of this water are not to be attributed to it solely as an article of diet: it often produces

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injurious or even fatal effects on the health of those who live near it, by contaminating the air which they breathe hence the prime importance of draining, not only large tracts of flooded land, but also small collections of stagnant waters, especially when situated near dwelling-houses. Water, when nearly or quite stagnant, sometimes becomes strongly impregnated with the mineral and vegetable substances with which it may be in contact. It is said that the valuable properties of Peruvian bark, in curing ague, were discovered in consequence of these having been imparted to water in which trees producing this bark had lain : and water in or near copper-mines sometimes becomes so charged with salts of copper, that it is a lucrative process to separate the copper from them. A good supply of water is of such vital importance to the existence of human society, that wherever mankind have settled for any length of time, and this has been wanting, either constantly or at times, they have taken measures to provide it, by tanks, aqueducts, and water-pipes. Some of the former are amongst the most remarkable works of human labour; but in modern times they have given way to the more convenient use of pipes, which improved knowledge in hydrostatics has generally introduced. The water supplied to communities by means of pipes has been supposed to be contaminated by the materials of which these pipes are composed. This idea, although not altogether groundless, has probably been much overrated. The iron pipes which are used for the larger conduits are but little acted upon, when filled with water, and excluded from the air; and the lead which is used for the smaller pipes seldom exhibits any considerable change, even after the lapse of several years.

Nevertheless, I cannot omit this opportunity of recommending a very simple expedient, which completely removes even the very trifling risk which is supposed to attend the use of lead: this consists in having the leaden pipes lined and covered by an extremely thin coating of tin, which is supposed to render them not only more wholesome, but more durable*.

Before I quit the subject of water, I must not omit to notice a very important method of purifying rain-, river- and stagnant-water, by means of filtration through charcoal. It has been employed upon a large scale, and with great advantage, in Paris; and it is coming into use in this country. Some bakers have very laudably employed it, for the purification of water used in making bread.

Next to plain water, I must mention, as little more than mere diluents, those drinks which consist principally of water; to which some other materials are added, for the purpose of communicating flavour, or perhaps rendering it a little more grateful to the stomach. In different countries, different materials, according to the different productions of the soil or taste of the inhabitants, are employed for this purpose.

TOAST-AND-WATER.-The simplest addition which is made to water, for the purpose of producing a light and agreeable beverage, is imparting to it the taste and colour of a piece of toasted bread. Its only advantage over simple water, for which it may at any time be substituted, seems to be, that, in consequence of the slight flavour which it receives, the disagreeable flatness which plain water, after standing awhile, always acquires, is not perceived. In some cases,

*Leaden pipes of this description are manufactured by my friend John Warner, of Jewin Crescent. See Note (9).