Abstract: The raw material NH₄HCO₃ and NaCl in the production of sodium carbonate accordingto the double decompositionNH₄HCO₃+ NaCl→NaHCO₃ + NH₄Cl (2)are plentiful in China. The main difficulty of the process technologically is the separatingNH₄Cl from the mother solotion I. In this paper the method of adding a middle salt,NH₄NO₃ or (NH₄)₂SO₄, has been studied. The middle salts can not change the place of thesaturated pointes of the reciprocal system in the dry-salt diagram evidently,but can prolongthe waiting time for crystallization of NaHCO₃ in the mother solution Ⅱ. The effect ofNH₄NO₃ is much better than that of (NH₄)₂SO₄.In adding NH₄NO₃, the waiting time isprolonged enough to separate tbe crystalline of NH₄Cl and the process of the fomula (2) become practicable.

Key words: Sodium carbonate, Middle salt, Ammonium bicarbonate, Double decomposition