[86] _Phil. Mag._, 1884 [5], 18. 210. See also Roozeboom, _Das Heterogene Gleichgewicht_, I. p. 177. [87] Brauns, _Neues Jahrbuch für Mineralogie_, 1900, 13. Beilage-Band, p. 39; Roozeboom, _Das Heterogene Gleichgewicht_, I. p. 181. [88] _Monatshefte_, 1888, 9. 435. [89] Gattermann, _Ber._, 1890, 53. 1738. [90] _Zeitschr. physikal. Chem._, 1889, 4. 468; _Annalen der Physik_, 1900 [4], 2. 649. [91] Quincke, _Annalen der Physik_, 1894 [3], 53. 613; Tammann, _Annalen der Physik_, 1901 [4], 4. 524; 1902, 8. 103; Rotarski, _ibid._, 4. 528. [92] _Annalen der Physik_, 1900 [4], 2. 649. [93] _Annalen der Physik_, 1902 [4], 8. 911. [94] See, more especially, O. Lehmann, _Annalen der Physik_, 1900 [4], 2. 649; Reinitzer, _Sitzungsber. kaiserl. Akad. zu Wien._, 1888, 94. (2), 719; 97. (1), 167; Gattermann, _loc. cit._; Schenck, _Zeitschr. physikal. Chem._, 1897, 23. 703; 1898, 25. 337; 27. 170; 1899, 28. 280; Schenck and Schneider, _ibid._, 1899, 29. 546; Abegg and Seitz, _ibid._, 1899, 29. 491; Hulett, _ibid._, 1899, 28. 629; Coehn, _Zeitschr. Elektrochem._, 1904, 10. 856: Bredig and Schukowsky, _ibid._, 3419. For a full account of the subject, the reader is referred to the work by Lehmann, _Flüssige Kristalle_ (Engelmann, 1904), or the smaller monograph by Schenck, _Kristallinische Flüssigkeiten und flüssige Kristalle_ (Engelmann, 1905). [95] A. C. de Kock, _Zeitschr. physikal. Chem._, 1904, 48. 129. [96] On account of the fact that all grades of rigidity have been realized between the ordinary solid and the liquid state, in the case both of crystalline and amorphous substances, it has been proposed to abandon the terms "solid" and "liquid," and to class bodies as "crystalline" or "amorphous," the passage from the one condition to the other being discontinuous; crystalline bodies possess a certain regular orientation of their molecules and a directive force, while in amorphous bodies these are wanting (see Lehmann, _Annalen der Physik_, 1900 [4], 2. 696). [97] Hulett, _loc. cit._ [98] Roozeboom, _Das Heterogene Gleichgewicht_, I. p. 144. See also Schenck, _Kristallinische Flüssigkeiten und flüssige Kristalle_, p. 8 (Engelmann, 1904). [99] The possible number of triple points in a one-component system is given by the expression (_n_(_n_ - 1)(_n_ - 2))/1.2.3, where _n_ is the number of phases (Riecke, _Zeitschr. physikal. Chem._, 1890, 6, 411). The number of triple points, therefore, increases very rapidly as the number of possible phases increases. [100] Duhem, _Zeitschr. physikal. Chem._, 1891, 8. 371. _Cf._ Roozeboom, _Das Heterogene Gleichgewicht_, p. 94 ff. [101] Roozeboom, _Das Heterogene Gleichgewicht_, I. p. 99. [102] Roozeboom, _Zeitschr. physikal. Chem._, 1888, 2. 474.