The phase rule and its applications . se of the octahedron, would yield a diagramsuch as is shown in Fig. 123. The projection of the edges ofthe octahedron form two axes at right angles and give rise tofour quadrants similar to those employed for the representationof ternary solutions (p. 276). Here, the point a represent- aternary solution saturated with respect to B and C ; and #P,quaternary solutions in equilibrium with the same two salts assolid phases. Such a diagram represents the conditions ofequilibrium only for one definite temperature, and corresponds,therefore, to the isothermal dia
The phase rule and its applications . se of the octahedron, would yield a diagramsuch as is shown in Fig. 123. The projection of the edges ofthe octahedron form two axes at right angles and give rise tofour quadrants similar to those employed for the representationof ternary solutions (p. 276). Here, the point a represent- aternary solution saturated with respect to B and C ; and #P,quaternary solutions in equilibrium with the same two salts assolid phases. Such a diagram represents the conditions ofequilibrium only for one definite temperature, and corresponds,therefore, to the isothermal diagrams for ternary systems(p. 276). In such a diagram, since the temperature and1 Lowenherz, Zeitschr. physikal. Chem., 1894, 13. 464. 320 THE PHASE RULE pressure are constant (vessels open to the air), a surface willrepresent a solution in equilibrium with only one solid phase;a line, a solution with two solid phases, and a point, one inequilibrium with three solid phases. Example.—As an example of the complete isothermal FanSO, mi. Fig. 124. diagram, there may be given one representing the equilibria inthe system composed of water and the reciprocal salt-pairsodium sulphate—potassium chloride for the temperature o°(Fig. 124).1 The amounts of the different salts are measuredalong the four axes, and the composition of the solution is 1 Meyerhoffer and Saunders, Zeitschr. physikal Chem., 1899, 28. 479. SYSTEMS OF FOlR COMPONENTS 321 expressed in equivalent gram-molecules per 1000 gram-mole-cules of The outline of this figure represents four ternary solutionsin which the component salts have a common acid or basicconstituent; viz. sodium chloride—sodium sulphate, sodiumsulphate—potassium sulphate, potassium sulphate—potassiumchloride, potassium chloride—sodium chloride. These foursets of curves are therefore similar to those discussed in theprevious chapter. In the case of sodium and potassium sul-phate, a double salt, glascrite [K3Na(S04)2] is
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