Protocarbonate of iron, or ferrous carbonate, is contained in a large number of mineral waters, in amount varying from mere traces to several grains in 16 oz. The most used and the most successful contain between 0.3 to 0.9 gr., with free carbonic acid.

It is a truism that minute quantities of iron taken at mineral springs, with the advantages of change, pure air, and often an elevated situation, produce effects as good as, or better than, can be obtained from medicinal doses administered in the ordinary manner. If 0.5 gr. be taken as an average proportion in 16 oz., then only this amount, representing but 0.14 gr. of metallic iron, is taken with each pint; but when once the condition has begun to improve, the iron contained in food is better assimilated, so that improvement is continued by natural processes. A few cubic inches of carbonic acid suffice to keep the iron salt in solution (Fre-senius), but on exposure to air part of the acid escapes, oxygen is absorbed, and hydrated ferric oxide is deposited. A chalybeate water will keep for some time if not shaken, and it may be heated up to 87° F. without much deposit of iron. A few waters contain sulphate or per-chloride.

Of alkaline waters, Gieshubel, Ems, Salzbrunn, Bilin, Luhatschowitz, Apollinaris - of alkaline saline springs, Carlsbad, Marienbad, Tarasp, Franzenbad - and of more markedly saline waters, Kissingen, Wiesbaden, Baden-Baden, Soden, Kreuznach, Rehme, Hall, Adelheidsquelle, and Harrogate, may all be mentioned as slightly chalybeate, and at almost all the great Spas there are some pure stronger chalybeates for use besides the saline; but among those frequented specially for the iron waters we may refer to the following:The Kniebis baths in the Badish Black Forest, twelve hundred to nineteen hundred feet above the sea, with beautiful scenery and quiet bath life.

Bocklet, near Kissingen, six hundred and twenty feet above sea-level, has a mild climate and a rich saline chalybeate water.

Driburg, near Paderborn, six hundred and thirty-three feet elevation, is situated in a pleasant valley, and has a fresh climate.

Konigsworth, near Marienbad, two thousand feet above the sea, in a sheltered position on the southern slope of a mountain, has a pure fresh climate recommended for chronic pneumonic and phthisical tendencies. The springs contain from 0.4 to 0.6 gr. of iron bicarbonate, 5 to 6 gr. of salts, and 30 cub. in. carbonic acid.

St. Moritz, in the Upper Engadine, a day's drive from the Coire station, situated in an Alpine valley, rich in vegetation, and five thousand four hundred feet above the sea, has become justly popular, for the air is very refreshing and agreeable even to delicate subjects, especially to those of sluggish circulation and unexcitable nervous system. It is clear and dry, and though dew falls, there is little fog or mist. For a winter residence it is also recommended. The springs contain 0.18 to 0.25 gr. of iron, with a little soda and lime and much carbonic acid (31 to 37 cub. in.), so that the baths are somewhat gaseous: temperature, 39° to 41° F. Santa Catarina, in Upper Italy, near Bormio, is even higher in situation (five thousand six hundred), and in waters and surroundings, and scenery, much resembles St. Moritz.

Pyrmont, in the principality of Waldeck, situated in a deep valley four hundred feet above the sea-level, with a healthy, mild climate, and extensive, somewhat old-fashioned arrangements, was formerly the most celebrated of iron Spas. It has one of the stronger compound springs, containing 0.57 of the mineral with lime, magnesia, and free carbonic acid (29 cub. in). There are also salt springs and baths.

Schwalbach, a clean, long-stretching town, on a sloping, sheltered plateau of the Taunus range is nine hundred feet above the sea. It is easily reached from Wiesbaden. It has pure fresh air, excellent arrangements, and strong iron springs, the Stahlbrunnen containing 0.64 gr., the Weinbrunnen 0.44 gr., the Paulinenbrunnen 0.51 gr., with lime, magnesia, soda, and much carbonic acid (40 to 50 cub. in.): temperature, 47° to 50° F.

Spa, in Belgium, one thousand feet above the sea, beautifully placed among the Ardennes forests, at the foot of a lofty wooded mountain, which shelters it on the north, is one of the most frequented iron springs on the Continent at any time from May till September; afterward the climate is apt to be wet and cold. The Pouhon spring contains 0.37 gr. of iron, with only 3 gr. of salines and 8 cub. in. carbonic acid. The Bari-sart has more gas and less iron.

At Harrogate, the Muspratt spring contains perchloride of iron with salines - an unusual and effective combination. The Tewit contains 0.135 gr. of carbonate, with a little saline.

Tunbridge Wells, about thirty miles south of London, three hundred feet above the sea, with healthy climate and beautiful environs, has a pure but weak spring, used formerly much more than it is at present. It contains about 1/4 gr. of iron oxide in the pint, but little carbonic acid, so that it is not sparkling. It might be taken with advantage in Apollinaris water.

At Brighton there is a spring, now but little used, which contains sulphate of iron in small amount, and at Malvern, Bournemouth, Sandown, and many other health-resorts there are chalybeates more or less available.