[137] _Ibid._, 1898, 27. 585. [138] See W. Guertler, _Zeitschr. anorgan. Chem._, 1904, 40. 268; Tammann, _Zeitschr. Elektrochem._, 1904, 10. 532. [139] E. von Pickardt, _Zeitschr. physikal. Chem._, 1902, 42. 17. [140] _Zeitschr. physikal. Chem._, 1904, 48. 467. [141] M. Padoa, _Accad. Lincei, Atti_, 1904, 13. 329. [142] Deville, _Compt. rend._, 1852, 34. 561; Payen, _ibid._, 1852, 34. 508; Debray, _ibid._, 1858, 46. 576. It has also been found by Jaffé (_Zeitschr. physikal. Chem._, 1903, 43. 465) that when spontaneous crystallization from solution occurs, the less stable form always separates first when purification has been carried sufficiently far. [143] Brauns, _Neues Jahrbuch für Mineralogie_, 1899, 13. (Beilage Band) 84. [144] _Lehrbuch_, II. 2. 445. See also _Principles of Inorganic Chemistry_, 2nd edit., p. 210 ff. [145] Schaum and Schönbeck, _Annalen der Physik_, 1902 [4], 8. 652. See also Chr. Füchtbauer, _Zeitschr. physikal. Chem._, 1904, 48. 549. [146] Ramsay and Young, _Phil. Trans._, 1886, 177. 87. [147] See volume in this series on _Chemical Dynamics_, by Dr. J. W. Mellor. [148] Isambert, _Compt. rend._, 1881, 92. 919; 1882, 94. 958; 1883, 96. 643. Walker and Lumsden, _Jour. Chem. Soc._, 1897, 71. 428. [149] _Compt. rend._, 1867, 64. 603. [150] _Compt. rend._, 1883, 102. 1243. [151] _Compt. rend._, 1868, 66, 1259. [152] Horstmann, _Ber._, 1876, 9. 749. [153] _Loc. cit._ [154] For the reasons for choosing anhydrous salt and water instead of salt hydrate and water as components, see p. 14. [155] See Ostwald, _Lehrbuch_, II. 2. 527. [156] Ostwald, _Lehrbuch_, II. 2. 538. [157] _Zeitschr. physikal. Chem._, 1889, 4. 43. [158] _Ber._, 1876, 9. 749. [159] See, for example, van't Hoff, _Lectures on Theoretical and Physical Chemistry_, I. p. 62 (Arnold). [160] _Jour. Chem. Soc._, 1877, 32. 395. [161] Hoitsema, _Zeitschr. physikal. Chem._, 1895, 17. 1. [162] _Zeitschr. physikal. Chem._, 1887, 1. 5; 1895, 17. 52. [163] It is important to powder the salt, since otherwise the dehydration of the hydrate and the production of equilibrium occurs with comparatively great tardiness. [164] A chemical individual is a substance which persists as a phase of constant composition when the conditions of temperature, pressure, and composition of the other phases present, undergo continuous alteration within certain limits--the limits of existence of the substance (Wald, _Zeitschr. physikal. Chem._, 1897, 24. 648). [165] Van't Hoff, _Zeitschr. physikal. Chem._, 1890, 5. 323; Ostwald, _Lehrbuch_, I. 606.