As is evident from the figure, addition of B raises the melting point of A, and, in accordance with the rule previously given, the concentration of B in the mixed crystals will be greater than in the solution. This is represented in the figure by the dotted curve AD. On the other hand, addition of A lowers the melting point of B, and the two curves BC and BE are obtained for the liquid and solid phases respectively. At the temperature of the line CDE the liquid solution of the composition represented by C is in equilibrium with the two different mixed crystals represented by D and E. At this temperature, therefore, the _tc_-curve for the solid phase exhibits a discontinuity; and, since the solid phase undergoes change at this point, the freezing-point curve must show a break (p. 111). [Illustration: FIG. 54.] Example.--Curves of the form given in Fig. 54 I. have been found experimentally in the case of silver nitrate and sodium nitrate.[274] The following table contains the numerical data, which are also represented graphically in Fig. 55:-- {191} ----------------------------------------------------- Molecules NaNO_{3} | Freezing point. | Melting point. per cent. | | ----------------------------------------------------- 0 | 208.6° | 208.6° 8 | 211.4° | 210° 15.06 | 215° | 212° 19.46 | 217.2° | 214.8° 21.9 | 222° | 215° 26 | 228.4° | 216.5° 29.7 | 234.8° | 217.5° 36.2 | 244.4° | 217.5° 47.3 | 259.4° | 237.6° 58.9 | 272° | 257° 72 | 284° | 274° 100 | 308° | 308° ----------------------------------------------------- The temperature of the transition point is 217.5°; at this point the liquid contains 19.5, and the two conjugate solid solutions 26 and 38 molecules of sodium nitrate per cent. respectively. [Illustration: FIG. 55.] [Illustration: FIG. 56.] (_b_) _The freezing-point curve exhibits a eutectic point_ (Curve II., Fig. 54). {192} In this case the freezing point of each of the components is lowered by the addition of the other, until at last a point is reached at which the liquid solution solidifies to a mixture or conglomerate of two mixed crystals. Examples.--Curves belonging to this class have been obtained in the case of potassium and thallium nitrates[275] and of naphthalene and monochloracetic acid.[276] The data for the latter are given in the following table and represented in Fig. 56:--