Abstract: A method for producing anhydrous alkali metal carbonates by mixing sodium bicarbonate with a stoichiometric equivalent of an alkaline metal hydroxide in an aqueous solution which reacts in an exothermic reaction to produce a thermally stable alkaline compound of the bicarbonate and hydroxide used, free of other compounds. On dehydrating, without the need of higher temperatures of calcination, one yields an anhydrous alkali metal carbonate or a mixed alkali metal carbonate depending on whether the alkali metal hydroxide used is not sodium but some other member of the alkali metal family. The active element on hydration of these mixed alkali metal carbonates is the alkali metal of the hydroxide used with the sodium bicarbonate to produce the anhydrous mixed alkali metal carbonate.