obstacle, when it pushes upwards, and welling out upon the surface, forms springs ; the water is therefore merely a modification of rain water. During its passage, however, it almost always takes up some soluble matters, which of course vary according to the nature of the soil. It is purest when it passes through sand or gravel; in a limestone region, it always contains more or less of the sulphate and carbonate of lime, and it generally contains a trace of common salt, and the usual proportions of air and carbonic acid gas. The presence of these is detected by subacetate of lead, which displays the smallest portion of carbonic acid or a carbonate, and nitrate of silver, which detects the muriates by the formation of muriate of silver. Water from melted ice is perfectly wholesome, and is drunk during the summer season, wherever the climate will admit of its being collected and preserved at a moderate expense. In this form, it is a luxury — almost a necessary — in the middle states of this country more particularly, " where," Dr. Dunglison remarks, " there is not a tavern on the road, on the eastern side of the Blue Ridge, that does not furnish ice to the traveller in any abundance." When sea-water freezes, the ice does not contain the salts. Consequently, when melted, it affords fresh water, and accord * The air in ice and snow water contains 34.8 per cent, of oxygen, while that in rain water contains but 32 per cent. 34 134 ing to the voyagers in high northern and southern latitudes, the water has been found sweet, soft, and wholesome. River Water. This is a mixture of rain and spring water, and when deprived of the matters which it frequently holds in suspension, is generally of consider- able purity. Mountain streams, which generally issue from siliceous rocks, and run over stony or pebbly beds, are, for the most part, comparatively pure and soft.. The river water of New-England, and the other hilly portions of the United States,, is usually of this description, though in the time of floods, and after heavy rains, they contain much sedimentary matter. River water gradually deposits much of its earthy salts as it flows, and becomes purer by exposure ; it there- fore generally contains less calcareous matter than spring water; its specific gravity is less, and its taste more vapid. It, however, more or less partakes of the nature of the soil over which it flows ; consequently some rivers, whose waters were pure and excellent at their source, lose these properties before they mingle with the sea. The water of the Thames, for example, in England, which is originally very soft and pure, becomes so loaded with animal and vege- table matter from the towns and villages on its banks, that after being kept a month or two in a closed cask, on opening it, a quantity of sulphuretted hydrogen gas, of the most offensive odor escapes, and the water is so black and nauseous as to be unfit for use. But on racking it off, it clears, depositing a quantity of slimy mud, and becomes remarkably clear, sweet and palatable. As the matters deposited in such rivers are merely mingled with the body of the water, which is too large, and too changing, to admit of any permanent taint from solution, filtration, or even the natural deposition of the ingredients fits them for every domestic and medicinal purpose. The following Table shows the solid contents of the Thames water* London, and of the Croton water t in the city of New-York. * Report from the Select Committee of the House of Lords, appointed to inquire into the supply of water to the Metropolis, p. 91, 1840. Analysis by R. Phillips, Esq. t Analysis, by Dr. J. R. Chilton, of New-York. 135 QUANTITY OF WATER. 1 Gallon = 10 lbs. Avoirdupois, at 62° Fah., or 70, grs. Avoirdupois. THAMES WATER. CROTON WATER. Brentford. Source of the Grand Junc- tion Water Works Com- pany. Chelsea. Source of the Chelsea Wa- ter WorkB Company. At its source CrotonLake In the City of New-York as it issues from the pipes. Carbonate of Lime,. ----„- Sulphate of Lime, > Chloride of Sodium, J Oxide of Iron, 1 Silica, 1 Magnesia, Carbonaceous Matter, J Chloride of Magnesium, ) Chloride of Calcium, / Carbonate of Magnesia, - - - - - Solid matter held in solution, -'-'--' Total solid matter, Grains. 16-000 3-400 very minute portions. Grains. 16-500 2-900 Ditto. Grains. 1-42 •00 •34 •86 •70 Grains. 1-52 •44 •46 •90 •84 19-400 0-368 19-400 0-238 2-98 •34 3-70 •46 19-768 19-638 3-32 416 Schuylkill Water. In 100 parts gr. in 1 gall. Analysis of the Croton and Schuylkill waters, by J. C