The yield of carbonization of ammoniacal brines with respect to Na and K ions was examd. by studying four reciprocal salt pair systems (NaCl(or NaNO3)-NH3-CO2,-H2O, KCl(or KNO3)-NH3-CO2H2O) with urea added, 8.26, 12.52 and 18,26 mol/kg H2O, at 298, 303, 308 and 313 K. The urea effect, i.e. the increased yield of carbonization with respect to Na ions, was explained by the formation of double salts, (NH4ClCO)-C-.(NH)(2) and NH,NO3-CO(NH2)(2). The increase with respect to K ions, was due to the salting-out effect of KHCO3 and due to the increased concns. of NH4Cl and NH4NO3 in the equil. soln.