“The carcass of a dead animal, thrown into a river or pond, and confined there, so as not to be borne off bodily, gradually wastes away, and, in a longer or shorter time, the main part of the carcass has disappeared. What has become of it? A part has been converted into gaseous products of decomposition, as the offensive odors observed during the decay will testify; but another portion has been carried off by the stream as soluble nitrogenous organic matter. This nitrogenous matter would be detected a short distance away, with greater or less ease, according to the volume of water present; but in a stream of large size, or in a lake at no very great distance from the source of contamination, it would be impossible to discover any offensive matter. There is a limit to the delicacy of our tests: there is a point beyond which, at the present, we are not able to go. At the present time, a chemical analysis alone is not sufficient to determine the desirability of a given water-supply.”--(Rivers Pollution Commission, 1874.) “The action of a float, upon or near the surface of the water, is no indication of the movement, back and forth, of the sewage in suspension. Portions of fresh sewage, it is true, will float, but after maceration the sewage has a specific gravity of about 1.325, and will sink, in still water, or very slow currents, at the rate of one foot per minute; but in a current of 170 feet a minute, it will not sink, but remain in suspension.”--(J. W. Adams, C. E., Water Supply Commission of Philadelphia, 1874.) “This evidence, taken in connection with our own investigations, appear to us, conclusively, to prove: “1st. That there is, at certain times, in human excreta, some material capable of producing disease, of a very fatal character, in human subjects. “2d. That this morbific matter can be detected only by its specific action upon human subject, and can not be distinguished, either by chemical or microscopical analysis, even in the concentrated excreta, much less in water mixed with the excreta. “3d. That, inasmuch as the organic matters of sewage are oxidized and destroyed with extreme slowness in running water, there is great probability that morbific matter will escape destruction and be conveyed to great distances in rivers and streams.”--(Rivers Pollution Commission, 1874.) “Carbonates of calcium and lime produce temporary hardness; while sulphate of lime and calcium and salts of magnesium produce permanent hardness. “Temporary hardness is objectionable for culinary and manufacturing purposes, and excessive hardness is productive of disease known as gravel. Magnesium salts are especially objectionable, because they cause diarrhœa and dyspepsia. Goitre, or swelling of the glands and cretinism, a kind of insanity, are charged to this impurity.