This, being derived from the conflux of numerous springs with rain water, unless in the immediate vicinity of a large town, generally possesses considerable purity; that the proportion of its saline contents should be small, is easily explained by the precipitation which must necessarily take place from the union of different solutions: it is, however, liable to hold in suspension particles of earthy matter, which impair its transparency, and sometimes its salubrity; it may also, in the neighbourhood of a city, hold dissolved, as well as suspended, a considerable proportion of animal and vegetable matter: this is unquestionably the case in the water supplied from the Thames by the Grand Junction Water Company; the discovery of the polluted source from whence this water flows into our houses, has lately filled the inhabitants with just alarm1. There exists a popular belief, that the water of the Thames is peculiarly adapted for the brewery of porter; it is only necessary to observe, that such water is never used in the London breweries. The vapid taste of river, when compared with spring, water, depends upon the loss of carbonic acid, from its long exposure.

It is well known that Thames water, by rest, undergoes a species of fermentation, and becomes free from organic matter, but Dr. Bos-tock has shewn that by the same process the saline contents are increased fourfold: the greatest proportionate increase being in the muriates, which are nearly twelve times more in the purified than in the ordinary state of the Thames water; the carbonate of lime is between two or three times as abundant as before, and the sulphate of lime between five and six times. So that the process of spontaneous depuration actually converts a soft. into a hard water. The source of these saline matters would appear to be the animal substances so copiously deposited in the Thames.

4. Well Water

Well Water is essentially the same as spring water, being derived from the same source; it is, however, more liable to impurity from its stagnation, or slow infiltration': hence our old wells furnish much purer water than those which are more recent, as the soluble particles are gradually washed away. Mr. Dalton observes, that the more any spring is drawn from, the softer the water will become.