[230] Gibbs, _Trans. Conn. Acad._, 3. 155; Saurel, _Journ. Phys. Chem._, 1901, 5. 35. [231] In the case of the fusion of a compound of two components with formation of a liquid phase of the same composition, the temperature is a maximum; in the case of liquid mixtures of constant boiling-point, the temperature may be a minimum (p. 105). [232] Roozeboom, _Zeitschr. physikal. Chem._, 1892, 10. 477. The formula of ferric chloride has been doubled, in order to avoid fractions in the expression of the water of crystallization. [233] Roozeboom, _Zeitschr. physikal. Chem._, 1892, 10. 477. [234] A similar series of hydrates is formed by zinc chloride and water (Dietz and Mylius, _Zeitschr. anorg. Chem._, 1905, 44. 209). [235] Meyerhoffer, _Ber._, 1897, 30. 1810. [236] Walden, _Ber._, 1899, 32. 2863. [237] _Zeitschr. physikal. Chem._, 1903, 42. 432. [238] This composition was also confirmed by measurements of the vapour pressure (cf. p. 90). [239] Since all substances are no doubt volatile to a certain extent at some temperature, it is to be understood here that the substances are appreciably volatile at the temperature of the experiment. [240] For a general discussion of the partial pressures in a system of two components, see Bancroft, _Journ. Physical Chem._, 1899, 3. 1. [241] _Zeitschr. physikal. Chem._, 1889, 3. 11; _Rec. trav. chim. Pays-Bas_, 1888, 7. 152. [242] The composition of a solution is represented symbolically by placing a double wavy line between the symbols of the components, and indicating the number of atoms present in the ordinary manner: thus, I [wavy] Cl_{_x_} represents a solution containing _x_ atoms of chlorine to one atom of iodine (Roozeboom, _Zeitschr. physikal. Chem._, 1888, 2. 450). [243] Since iodine monochloride in the liquid state is only very slightly dissociated, the bend at C is very sharp (see p. 147, footnote). See also the investigation of the system pyridine and methyl iodide (Aten, _Versl. Konink. Akad. Wetensch. Amsterdam_, 1905, 13. 462). [244] This upper branch of the curve is not shown in the figure, as the ordinate corresponding to 30° would be very great. [245] Stortenbeker, _Zeitschr. physikal. Chem._, 1889, 3. 22. [246] Ramsay and Young, _Journ. Chem. Soc._, 1886, 49. 458. [247] Van't Hoff, _Lectures on Physical Chemistry_, I. p. 77 (Arnold). [248] This is different from what we found in the case of non-volatile solutes (p. 126). In the present case, the _partial pressure_ of the iodine in the vapour will be lowered by addition of chlorine, but the _total pressure_ is increased. [249] The diminution of volume is supposed to be carried out at constant temperature. The pressure and the composition of the phases must, therefore, remain unchanged, and only the relative amounts of these can undergo alteration.