Carbonic Acid Sources

CARBONIC ACID SOURCES. Carbonic acid can be present in water in free and semi-bound states (bound carbonic acid, when free CO₂ is present, converts to semi-bound bicarbonate ion HCO₃). CO₂ is a component of almost all mineral waters, because water saturated with carbonic acid acquires the property of dissolving substances insoluble in ordinary water. James called CO₂ the 'passport of mineral waters'. However, not every water containing CO₂ can be called carbonic. For inclusion in the class of carbonic waters in the narrow sense, the mineral water must satisfy three basic requirements: 1) the amount of free CO₂ must exceed 1 g per 1 kg of water (or 507.2 cm³ at 0° and 700 mm pressure); 2) the dry residue of the water must be less than 1 g per 1 kg; 3) the water must not contain substances whose presence, even in small amounts, would require classifying this water in another category (e.g., 0.03 or more of iron ions). Many carbonic acid sources contain significantly larger amounts of free CO₂: for example, in the water of the Grosser Sprudel source in Naugheim there is 3.9 g of free CO₂ or, converted to volume relations, 2,247 cm³ of CO₂ at the temperature of the source water 29°. A high content of free CO₂ is also characteristic of some sources in Siberia (Darasun from 2.9 to 4.0 g). Carbonic waters are used as medicinal and table waters, as well as for carbonic baths (see).