A survey of reported compositions along the saturation curve (sat), and compositions of coexisting phases in equilibrium (eq.) for the system 1-butanol-toluene-water is given in Table 77.

Saturation curve The system 1-butanol-toluene-water forms a miscibility gap of type 2. Two binary systems, 1-butanol-water and toluene-water, are partially miscible. The data of these systems were compiled and critically evaluated in previously published SDS volumes, Refs. 4 and 5, respectively. The recommended values of mutual solubility at 298.2 K are x'₂=0.9972, x"₂=0.000 104 for toluene-water system⁴ and x'₁=0.488, x"₁=0.0191 for 1-butanol-water.⁵ The saturation curve for the organic-rich phase was measured by Fuoss¹ by the conductance method; the water-rich phase was assumed to be toluene free. Shanahan² measured only the saturation curve at 293 K. Letcher and Siswana reported both saturation and equilibrium results at 298 K. Each of these reported measurements was made at a different temperature and therefore no recommendation can be made. However, all these data are consistent with one another. All three data sets are treated as tentative. The maximum 1-butanol concentration was observed in the organic-rich branch of the saturation curve at each reported temperatures, in the area of x₁=0.54±0.01 and x₂=0.11±0.02. The saturation mixtures of the water-rich branch contained undetectably small amounts of toluene; the water-rich phase was reported as a binary 1-butanol-water mixture by both Refs. 1 and 3. The temperature of 298 K was chosen for graphical presentation and therefore only experimental data of Letcher and Siswana³ are shown in Figure 41 . The binary data reported with ternary data sets are in agreement with the previously recommended binary solubility data.

Phases in equilibrium Compositions of coexisting phases in equilibrium for the ternary 1-butanol-toluene-water system were reported in Refs. 1 and 3, at 303 and 298 K respectively, and cover the whole range of the miscibility gap. The tie lines are consistent within each data set, but the data sets are inconsistent with one another because tie lines cross. It is unlikely that a temperature difference of 5 K gives such large changes in phase composition e.g., water-rich phase x₁=0.007 in equilibrium with organic-rich phase x₁=0.341, x₂=0.570 at T/K=298, Ref. 3; and water-rich phase x₁=0.0063 in equilibrium with organic-rich phase x₁=0.0609, x₂=0.9291 at T/K=303, Ref. 1. Both equilibrium data sets are treated as tentative. The experimental tie lines at 298 K by Letcher and Siswana, Ref. 3, are presented in Figure 41 .