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Natural waters containing special constituents not present (except in traces) in ordinary water are known as mineral waters. They are of several kinds:- Acidulous waters contain dissolved carbon dioxide, together with alkali bicarbonates, and common salt. The carbon dioxide may be liberated with effervescence when the water is slightly warmed, e.g., Apollinaris and Seltzer (i.e., Selters) waters. Some acidulous waters contain sulphuric acid, probably derived from the oxidation of sulphur dioxide or iron pyrites.
- Chalybeate, or ferruginous waters, containing ferrous bicarbonate. On exposure to air, such water deposits brownish-red ferric hydroxide. E.g., Pyrmont water.
- Hepatic waters (Latin hepar, liver), contain hydrogen sulphide, H2S, and alkali sulphide, e.g., Na2S. They smell of hydrogen sulphide, and on exposure to air deposit sulphur: 2H2S + O2 = 2H2O + 2S. Harrogate water is of this type.
- Alkaline waters, e.g., Vichy water, contain sodium bicarbonate, NaHCO3, and sometimes lithium bicarbonate, LiHCO3, which are supposed to be beneficial in the treatment of gout.
- Bitter waters contain various dissolved salts. E.g., Marienbad water (sodium sulphate); Epsom water (magnesium sulphate); Friedrichshall and Hunyadi-Janos waters (sodium and magnesium sulphates)
- Siliceous water contains dissolved silica and alkali silicates. Such waters, e.g., of the geysers of Iceland, New Zealand, and Yellowstone Park (America), are usually almost boiling, and deposit masses of siliceous sinter at the mouth of the geyser.
- Iodine water contains dissolved iodides, and occurs at Woodhall Spa (Lincoln), and in Central Europe.
- Hot springs occur in various places, e.g., Buxton (28°) and Bath (47°). They often contain dissolved gas, including helium, and traces of radium emanation.
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