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The solubility in the system NaCl3(C 2 H 5 ) 2 NH3H 2 O at 50oC was studied. The shape of the solubility isotherm was analyzed.The NaCl3(C 2 H 5 ) 2 NH3H 2 O system at 50oC, which determines the preparation conditions of a saturated solution of sodium chloride (mass fraction of NaCl is 26% [133]) and diethylamine, has not been described in the literature. The phase equilibria in the NaCl3 (C 2 H 5 ) 2 NH3H 2 O system are known only for 10, 20, and 30oC [1,2].The main method of studying solubility is the modified method of residue [335]. In the modified method, we used the compositions of the saturated solution and initial reaction mixture, instead of residue, to calculate the composition of the equilibrium solid phase. The mass ratio of the components in the initial mixture samples was chosen so that the compositions were heterogeneous and the mass ratios of the solid to liquid phase did not exceed 2 : 5. When studying the monotectic region, in which two liquid phases and NaCl crystals coexist, we used the halfsum of the contents of the system components in the upper and lower liquid phases. Equilibration was judged by constancy in three measurements of the refractive index of the liquid phase, which is a physical property of a medium that can be determined readily and accurately. The measurements were performed on an RL1 refractometer in 30-min intervals. The measurements started after thermostating for 3 h at 50 + 0.1oC.The Na + ions were determined by the flame photometry on a Zeiss photometer and an F-30 digital recorder. Practically, the determination was performed as follows: Three different weighed portions, sampled after the thermostating, were placed into 0.1 dm 3 volumetric flasks, and distilled water was added to the mark. Then the flame intensity was determined with samples from all the three flasks. After that, the intensity of 335 reference solutions was measured. We used reference NaCl solutions of the concentrations from 0.0001 to 0.1 mol dm 33 , prepared from reference samples.The concentration of the Na + ions was determined from the linear dependence of the flame intensity on the logarithm of the concentration. The molal concentrations of the sodium ions (mol kg 31 ) in the weighed portions were calculated by the formula: c Na + VR [Na + ] = ÄÄÄÄÄÄ, (1) m where c Na + is the molar concentration of a sodium cation in the volumetric flask, as determined by the linear interpolation (mol dm 33 ); V, flask volume (ml); R, dilution of the solution; and m, mass of the weighed portion m (g). The unknown quantity was determined as the mean of the three obtained values.The content of the chloride ions was determined by argentometric titration [4,5]. The equivalent point was determined from the functional dependence of the silver electrode potential on the amount of the AgNO 3 solution added. A glass electrode was the reference. The test solution was acidified with an 85% H 3 PO 4 solution (1 ml). The potential of the silver electrode in the course of the titration was measured with an EV-74 pH meter.The ...

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