| Point. | Solid phases. | Composition of solution in gram-mols. per 1000 gram-mols. water. | |||
| NaHCO3 | NaCl | NH4HCO3 | NH4Cl | ||
| — | NaHCO3 | 1.08 | — | — | — |
| — | NaCl | — | 6.12 | — | — |
| — | NH4HCO3 | — | — | 2.36 | — |
| — | NH4Cl | — | — | — | 6.64 |
| I. | NaHCO3; NaCl | 0.12 | 6.06 | — | — |
| II. | NaCl; NH4Cl | — | 4.55 | — | 3.72 |
| III. | NH4Cl; NH4HCO3 | — | — | 0.81 | 6.40 |
| IV. | NaHCO3; NH4HCO3 | 0.71 | — | 2.16 | — |
| P1 | NaHCO3; NH4HCO3; NH4Cl | 0.93 | 0.51 | — | 6.28 |
| P2 | NaHCO3; NaCl; NH4Cl | 0.18 | 4.44 | — | 3.73 |
With reference to the solution represented by the point P1, it may be remarked that it is an incongruently saturated solution (p. [279]). If sodium chloride is added to this solution, the composition of the latter undergoes change; and if a sufficient amount of the salt is added, the solution P2 is obtained.
Turning now to the practical application of the data so obtained, consider first what is the influence of concentration on the yield of soda. Since the reaction consists essentially in a double decomposition between sodium chloride and ammonium bicarbonate, then, after the deposition of the sodium bicarbonate, we obtain a solution containing sodium chloride, ammonium chloride, and sodium bicarbonate. In order to ascertain to what extent the sodium chloride has been converted into solid sodium bicarbonate, it is necessary to examine the composition of the solution which is obtained
with definite amounts of sodium chloride and ammonium bicarbonate.
Consider, in the first place, the solutions represented by the curve P2P1. With the help of this curve we can state the conditions under which a solution, saturated for ammonium chloride, is obtained, after deposition of sodium bicarbonate. In the following table the composition of the solutions is given which are obtained with different initial amounts of sodium chloride and ammonium bicarbonate. The last two columns give the percentage amount of the sodium used, which is deposited as solid sodium bicarbonate (UNa); and likewise the percentage amount of ammonium bicarbonate which is usefully converted into sodium bicarbonate, that is to say, the amount of the radical HCO3 deposited (UNH4):—
| Point. | Initial composition of the solutions: grams of salt to 1000 grams of water. | Composition of solutions obtained: gram-equivalents per 1000 grams of water. | UNa per cent. | UNH4 per cent. | ||||
| NaCl | NH4HCO3 | HCO3 | Cl | Na | NH4 | |||
| P2 | 479 | 295 | 0.18 | 8.17 | 4.62 | 3.73 | 43.4 | 95.1 |
| — | 448 | 360 | 0.31 | 7.65 | 3.39 | 4.56 | 55.7 | 93.4 |
| — | 417 | 431 | 0.51 | 7.13 | 2.19 | 5.45 | 69.2 | 90.5 |
| P1 | 397 | 496 | 0.92 | 6.79 | 1.44 | 6.28 | 78.8 | 85.1 |
This table shows that the greater the excess of sodium chloride, the greater is the percentage utilization of ammonia (Point P2); and the more the amount of sodium chloride decreases, the greater is the percentage amount of sodium chloride converted into bicarbonate. In the latter case, however, the percentage utilization of the ammonium bicarbonate decreases; that is to say, less sodium bicarbonate is deposited, or more of it remains in solution.
Consider, in the same manner, the relations for solutions represented by the curve P2IV, which gives the composition of solutions saturated with respect to sodium bicarbonate and ammonium bicarbonate. In this case we obtain the following results:—