The effect upon the system of each one of these substances, or combination of them, when occurring in water is the same as when given in ordinary prescriptions, but there is a point beyond which chemistry has not penetrated; for instance, a glass of some mineral waters, containing but a few grains of solid matter in solution will often produce a quicker and more powerful effect when taken than twice the amount of the solid constituents, shown to be present by analysis, prepared artificially by the apothecary. The reason of the efficacy of some mineral waters may be in unrecognized combustion of known elements or the presence of substances as yet beyond the power of chemistry to detect. Four of these common substances mentioned above have a characteristic taste, and as they are all found in nearly every well, it follows that these waters must have _some_ taste. This, as already stated, is a fact. We, who are accustomed by constant use to one particular well, fail to recognize any taste at all, while a stranger will often detect it at once. Distilled pure water tastes “flat” and very disagreeable to us, because we miss the salts and gases, which distillation has removed. A chemist will often work in an atmosphere filled with noxious and powerfully smelling gases, but will not be able to perceive them, though a stranger would not only notice them at once, but with great difficulty endure them. The mineral constituents in well or river water will average five to thirty grains per gallon; while they vary in amount, as shown from analysis from one-twentieth to twenty thousand grains per gallon.[2] Waters containing much lime or magnesia, are called “hard,” and are the only kind found in some sections of our country. Besides the common mineral constituents of water, there are others, which have been occasionally detected, such as arsenic, barium, strontium, lithium, bromine, iodine, fluorine, zinc, copper, lead, silver, antimony, nickel, cobalt, &c., &c. It will be noticed that many of these are poisonous, but nature suffers their presence, in minute quantities only,—except in rare instances,—while the localities having metallic elements in their waters are few and chiefly among mines and ore-beds. These substances rarely occur in our wells and springs and hence they need no particular consideration here, though, if present, only analysis is a safe means of detection. Where water contains a large amount of mineral matter, it has a decided effect upon the digestive organs, and, after shorter or longer use, tends to produce diseases, such as dyspepsia, constipation, gravel, &c., &c. But waters with a large enough amount of mineral matter to give them a decided taste, are called “mineral waters” and are used rather as medicine, than as a habitual means of slaking thirst.