[343] The influence of pressure on the transition point in the case of tachydrite has been determined by van't Hoff, Kenrick, and Dawson (Zeitschr. physikal. Chem., 1901, 39. 27, 34; van't Hoff, Zur Bildung der ozeanischen Salzablagerungen, I. p. 66—Brunswick, 1905). This salt is formed from magnesium chloride and calcium chloride at 22°, in accordance with the equation—
2MgCl2.6H2O + CaCl2.6H2O = Mg2CaCl6.12H2O + 6H2O
Increase of pressure raises the transition point, because the formation of tachydrite is accompanied by increase of volume; the elevation being 0.016° for an increase of pressure of 1 atm. The number calculated from the theoretical formula (p. [57]) is 0.013° for 1 atm.
If one calculates the influence of the pressure of sea-water on the temperature of formation of tachydrite (which is of interest on account of the natural occurrence of this salt), it is found that a depth of water of 1500 metres, exerting a pressure of 180 atm., would alter the temperature of formation of tachydrite by only 3°. The effect is, therefore, comparatively unimportant.
[344] Roozeboom, Zeitschr. physical. Chem., 1887, 1. 227.
[345] Zeitschr. physical. Chem., 1887, 1. 227.
[346] Van't Hoff and Müller, Ber., 1898, 31. 2206.
[347] Van't Hoff and van Deventer, Zeitschr. physikal. Chem., 1887, 1. 165.
[348] For a full discussion of the solubility relations of sodium ammonium racemate, see van't Hoff, Bildung und Spaltung von Doppelsalzen, p. 81.
[349] Annales chim. phys., 1848 [3], 24. 442.