Salt-carbon dioxide baths in which a precipitate is not formed even at elevated temperatures are produced by dissolving a minor proportion of a water-soluble colloid in tap water and mixing the solution with an alkali-metal bicarbonate.  The term "Salt" is defined as sodium chloride, alkali-metal bicarbonate, and those normally present in tap water capable of entering into precipitation reaction with alkali-metal bicarbonates.  The amount of colloid required may be reduced by adding sodium chloride and/or treating the colloid polution with carbon dioxide prior to the addition of the alkali-metal bicarbonate.  A hot clear common salt-sodium bicarbonate sol may be prepared with the water soluble colloid additive and the tap water containing the carbon dioxide may be added to produce the required bath.  Examples of colloids are gelatina alba; carbohydrates e.g. dextrin; alginates or alginic acid esters having a molecular weight between 8,800 and 176,000 e.g. sodium alginate; cellulose ethers e.g. the sodium salt of cellulose glycoalic acid ether which contains about 7 per cent. of fixed sodium, has a degree of polymerization of about 250, a molecular weight of about 54,000, a viscosity in 2 per cent. solution at 20 DEG C. of about 25 centipoise (Höppler) and in which there is one etherized side chain for each cellobiose part and on an average one additional side chain of the same type attached to every third or fourth cellabiose part; polyacrylic acid or a sodium salt thereof having a pH about 6,5, specific viscosity of about 170 and molecular weight of about 95,000 or of pH 3,0, specific viscosity of about 30 and a molecular weight of about 30,000.ALSO:Salt-carbon dioxide baths in which a precipitate is not formed even at elevated temperatures, are produced by dissolving a minor proportion of a water-soluble colloid in tap water and mixing the solution with an alkali metal bicarbonate in the amount necessary to produce the desired therapeutic effect.  The term "salt" is defined as sodium chloride, alkali metal bicarbonates and those normally present in tap water capable of entering into precipitation reaction with alkali metal bicarbonates.  The amount of colloid required may be reduced by adding sodium chloride and/or treating the colloid solution with carbon dioxide prior to the addition of the alkali metal bicarbonate.  A hot clear common salt-sodium bicarbonate sol may be prepared with the water-soluble colloid additive and the tap water containing the carbon dioxide may be added to produce the required bath. Examples of colloids are gelatina alba; carbohydrates, e.g. dextrin; alginates or alginic acid esters having a molecular weight between 8,800 and 176,000, e.g. sodium alginate; cellulose ethers e.g. the sodium salt of cellulose glycolic acid ether which contains about 7 per cent of fixed sodium, has a degree of polymerization of about 250, a molecular weight of about 54,000, a viscosity in 2 per cent solution at 20 DEG C. of about 25 centipoise (Höppler) and in which there is one etherized side chain for each cellobiose part and on an average one additional side chain of the same type attached to every third or fourth cellobiose part; polyacrylic acid or a sodium salt thereof having a pH about 6.5, specific viscosity of about 170, and molecular weight of about 95,000, or of pH 3.0, specific viscosity of about 30 and a molecular weight of about 30,000.