To make these observations more intelligible we may mention a few instances of known waters, with their place in the scale. In Keswick the water is under half of hardness; in Lancaster it is le i • and in Manchester, 2°. The water of the Dee at Aberdeen. which is used for the supply of the town, is if of hardness. The water of loch Katrine is of great purity, having only two grains of solid matter of all kinds in the gallon, and 1° of hardness. The waters of the Welsh mountains, from which it has been proposed to supply London, have on an ayerage less than 2°. The river Clyde, which formerly supplied Glasgow, is and may also be reckoned a soft water. The Thames at London, as well as the New river, is about 14°, while many of the tributaries of the Thames rise as high as 16°; but being all chalk-waters, they may be materially softened by boiling. Springs from the chalk commonly range from 16° to 18°; but par ticular springs arc to be met with in some parts of the world four or five times as hard, from the presence of bicarbonate of lime. The water of the treasury pump in London has from 50° to 60° of hardness. In many parts of the continent hard waters abound; but the testing of waters has not been so much attended to there as in this country.
The evidence laid before the royal commission above referred to went to prove that there is no reason whatever to suppose that the hardness of the Thames water, which averages about 15°, would be in the least degree prejudicial to health. It appears that the hardness of springs is generally considerable; and that surface-waters may be col-, lected in a state that is to be considered soft Lead in effects have frequently arisen from the contamination of water with lead, derived from leaden pipes and cisterns. Some kinds of water are known to act powerfully on a leaden surface, and others scarcely at all; but the qualities and circumstances on which the action depends have never been satisfactorily determined. Distilled water, and soft lake and river waters in general, act most decidedly, but by na means in proportion to their softness. The presence of air in the water seems one essen tial condition; light also increases the action, as does the presence of vegetable matter; it has been observed that when leaves drop by chance into a lead cistern, the spots where they lie become visibly corroded. The water of lobli Katrine, according to extensive' sets of expriments by distinguished chemists, is allowed to have an intense action* on lead under certain circumstances—viz., "1st, If the lead be bright and highly polished; and 2d, If the lead and water be freely exposed to the access of air." But it "does not
exert any noxious action on lead when the metal is in its ordinarily dull state." The coating formed on the surface of the metal is held to protect it from further chemical action. Still there are opposing facts to show that this protective action is not always to be relied on; and that water that has passed through any considerable length of lead pipe, or stood for sonic time in a short one, or in a cistern, should never be used without care; a ninth part of a grain of lead per gallon has been known to derange the health of a whole community. Dr. Clark made the unexpected discovery that sand-filters com pletely separate the lead.
Organic contamination of water by vegetable and animal substances takes place in various ways. The most obvious and abundant source of this class of ingredients is the sewage and refuse of towns; and next in order may be ranked the con tact with soils rich in organic matter. Among organic impurities may be classed offen sive gases, such as carbureted, sulphureted, and phosphureted hydrogen; vegetable fibers in a state of rottenness; putrefying products of the vegetable or animal kingdoms; starch, muscular fiber, etc.; urea and ammoniacal products; vegetable forms—algae, confervce, fungi, etc.; animalcules—infusoria, entomostracem, annelidm or worms, etc. Water falling on a growing soil, and running off the surface to lie in stagnant ponds, is in very favorable circumstances for being tainted with vegetable and animal life. Water-plants will spriug up and feed numerous tribes of animalcules, and each pool will be a constant scene of vitality. In such a state the water is usually unfit for chinking; the palate instantly discerns a disagreeable taint, and no one will use it who can do bet ter. The surface-water of a district overgrown with peat-moss has usually a peaty flavor, as well as a dark and dirty color. The infusion of peat does not breed animal cules, being a strong antiseptic; but it is an objectionable ingredient nevertheless. Very slow filtration has been found to remove the color of the infusion in some degree, but not entirely. Lime removes the peat most effectually, but there is both expense and risk in applying it. It is perhaps doubtful whether any specific unwholesomeness can be justly attributed to peat-water; but it is unpalatable, and the use of it is shunned by the inhabitants of peaty districts, and even by cattle. The presence of peat in the lands used as collecting-grounds for surface-water—and it is generally such worthless tracts that are so employed—is a disadvantage attending that mode of supply.