[250] At point _b_ the ratio of chlorine to iodine in the solution is less than in the monochloride, so that by the separation of this the excess of chlorine yielded by the condensation of the vapour is removed. [251] Roozeboom, _Rec. trav. chim. Pays-Bas_, 1884, 3. 29; 1885, 4. 65; _Zeitschr. physikal. Chem._, 1888, 2. 450. [252] Two curves "enclose" a field when they form with one another an angle less than two right angles. [253] Roozeboom, _Zeitschr. physikal. Chem._, _loc. cit._ [254] Van't Hoff, _Zeitschr. physikal. Chem._, 1890, 5. 323. [255] Bancroft has proposed to restrict the term "occlusion" to the formation of solid solutions, and to apply "adsorption" only to effects which are primarily due to surface tension. Such a distinction, however, would probably be very difficult to carry through, for although adsorption may, in large measure, be due to surface tension, the behaviour of adsorbed substances is similar to that of substances existing in solid solutions. [256] Tammann, _Wied. Annalen_, 1897, 63. 16; _Zeitschr. physikal. Chem._, 1898, 27. 323. [257] See, for example, Chappuis, _Wied. Annalen_, 1881, 12. 161; Joulin, _Annal. chim. phys._, 1881, [5], 22. 398; Kayser, _Wied. Annalen_, 1881, 12. 526. [258] Hoitsema, _Zeitschr. physikal. Chem._, 1895, 17. 1. [259] _Annales chim. phys._, 1874, [5], 2. 279. [260] Hoitsema, _Zeitschr. physikal. Chem._, 1895, 17. 1; Dewar, _Phil. Mag._, 1874, [4], 47, 324, 342; Mond, Ramsay and Shields, _Proc. Royal Soc._, 1897, 62. 290. [261] _Loc. cit._ [262] It is noteworthy that the form of curve obtained for hydrogen and palladium bears a striking resemblance to that for the dehydration of colloids containing absorbed water, _e.g._ silicic acid (_vide_ van Bemmelen, _Zeitschr. anorg. Chem._, 1897-1900. Cf. Zacharias, _Zeitschr. physikal. Chem._, 1902, 39. 480). [263] _Zeitschr. physikal. Chem._, 1890, 5. 322. [264] Küster, _Zeitschr. physikal. Chem._, 1895, 17. 367. Bodländer, _Neues Jahrbuch f. Mineralogie_, 1898-99, Beilage Band, 12. 92. [265] Bruni and Padoa, _Atti Accad. Lincei_, 1902 [5], 11. 1; 565. [266] Roozeboom, _Zeitschr. physikal. Chem._, 1899, 30. 385; Bruni, _Rend. Accad. Lincei_, 1898, 2. 138, 347. For a general account of "solid solutions" the reader is referred to Bruni, "_Ueber feste Lösungen_" (Ahrens'sche Sammlung), and to Bodländer, _loc. cit._ For the formation and transformation of liquid mixed crystals, see A. C. de Kock, _Zeitschr. physikal. Chem._, 1904, 48. 129. [267] In discussing the various systems which may be obtained here, Roozeboom (_loc. cit._) made use of the variation of the thermodynamic potential (p. 29) with the concentration. In spite of the advantages which such a treatment affords, the temperature-concentration diagram has been adopted as being more readily understood and as more suitable for an elementary discussion of the subject. [268] These curves are also called the "liquidus" and the "solidus" curve respectively.