For our present purpose it is sufficient to pick out only some of the equilibria which have been studied, and which are represented in the model (Fig. 119). In this case use has been made of the triangular method of representation, so that the surface of the model lies within the prism. [Illustration: FIG. 119.] This model shows the three surfaces, A, B, and C, which represent the conditions for the stable existence of the salts B_{1-1-1}, S_{10}, and S_{3} in contact with solution at different {300} temperatures. The front surface of the model represents the temperature 9°, and the farther end the temperature 75.5°. The dotted curve represents the isotherm for 20°. The prominences between the surfaces represent, of course, solutions which are saturated in respect of two solid phases. Thus, for example, _pabc_ represents solutions in equilibrium with B_{1-1-1} and S_{10}; and the ridge _qdc_, solutions in equilibrium with S_{10} and S_{3}. The point _b_, which lies at 75.5°, is the point of maximum temperature for S_{10}. If the temperature is raised above this point, S_{10} decomposes into the basic salt B_{1-1-1} and solution. This point is therefore analogous to the point M in the carnallite model, at which this salt decomposes into potassium chloride and solution (p. 284); or to the point at which the salt 2FeCl_{3},2HCl,12H_{2}O decomposes into 2FeCl_{3},12H_{2}O and solution (p. 294). The curve _pab_ has been followed to the temperature of 72° (point _c_). The end of the model is incomplete, but it is probable that in the neighbourhood of the point _c_ there exists a quintuple point at which the basic salt B_{1-2-2} appears. In the neighbourhood of _e_ also there probably exists another quintuple point at which S_{4} is formed. These systems have, however, not been studied. The following tables give some of the numerical data:-- ISOTHERM FOR 20°.