The phase rule and its applications . r. physikal. Chem., 1899, 30. 446. 2 See in this connection the volume in this series on Electro-chemistry,by Dr< R. A. Lehfeldt. APPENDIX 343 for determining the transition point of a salt, when we bear inmind that at the transition point the solubility of the two formsbecomes identical. Thus, for example, the transition point of zincsulphate heptahydrate into hcxahydrate could be determined in thefollowing manner. Tube A (Fig. 134 contains, say, a saturatedsolution of the heptahydrate along with some of the solid salt ; tubeB, a saturated solution of
The phase rule and its applications . r. physikal. Chem., 1899, 30. 446. 2 See in this connection the volume in this series on Electro-chemistry,by Dr< R. A. Lehfeldt. APPENDIX 343 for determining the transition point of a salt, when we bear inmind that at the transition point the solubility of the two formsbecomes identical. Thus, for example, the transition point of zincsulphate heptahydrate into hcxahydrate could be determined in thefollowing manner. Tube A (Fig. 134 contains, say, a saturatedsolution of the heptahydrate along with some of the solid salt ; tubeB, a saturated solution of the hcxahydrate along with the solid tube C is a connecting tube bent downwards so as to preventthe mixing of the solutions by convection currents. ZZ are two zincelectrodes immersed in the solution ; the cell is placed in a ther-mostat and the zinc electrodes connected with a , now, at temperatures below the transition point the solubilityof the hcxahydrate (the metastable form) is greater than that of the. Fig. 134 heptahydrate, a current will be produced, flowing in the cell fromheptahydrate to hexahydrate. As the temperature is raisedtowards the transition point, the solubilities of the two hydratesalso approach, and the current produced will therefore becomeweaker, because the of the cell becomes less ; and when thetransition point is attained, the becomes zero, and the currentceases. K the temperature is raised above this, the solubility of theheptahydrate becomes greater than that of the hexahydrate, and acurrent will again be produced, but in the opposite direction. Bynoting the temperature, therefore, at which the current ceases, or becomes zero, the transition temperature can be the case just described, the electrodes consisted of the samemetal as was contained in the salt. But in some cases, sodiumsulphate, electrodes of the metal contained in the salt cannot beemployed. Nevertheless, the above e
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