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^XL. On the Connexion between Freezing-points, Boiling- 

 points, and Solubilities. By Meyer Wildermax, Ph.D., 

 B.Sc. (Oxon.)*. 



A.TN Comptes Rendus, lxx. p. 1349 (1890), Guldberg gave 

 JL the connexion between the lowering of freezing-point 

 iind lowering of vapour-pressure of solutions. In a similar 

 manner van't Hoff and Roozeboom connected two vapour- 

 pressure curves meeting at one common point {the point of 

 transition) , belonging to two hydrates of the same salt, or to the 

 same substance in two different alio tropic states, &c. (see van't 

 Hoff's Studien zur chemischen Dynamik. translated by Ernst 

 Cohen, pp. 235, 247, also 226). In this paper the connexion 

 between the freezing-point, boiling-point, and solubility curves 

 will be considered. 



Le Chatelier and van't Hoff have deduced the following 

 thermodynamic equations for the solubility curve, which are 

 analogous to those of Clausius for the vapour-pressure curve: — 



jm = "nnFo where /> is the concentration, T the absolute 



ill Hi" 71 



temperature, q the heat of solution (Le ( Jhatelier) ; -jFp = r^- 2 , 



where p is the osmotic pressure of the solution (van't Hoff'). 

 Taking into further account the connexion between the con- 

 centration of the solution, G, and its osmotic pressure, p, we 



g dT = 2T* non-electrolytes, and -^- = ^p £or 



electrolytes, (A), where q is not independent of tem- 

 perature ; putting q = q + a,T, the above equations assume 

 the form 



dlgnC _, q + *T dlgnC_g + a,T 



dT 2T2 and dT ■ 2 . T2 ^ 



The considerations involved in the deduction of the above 

 equations show that they will, as a general rule, apply best 

 to dilute solutions, i. <?., of substances of small solubility, and 

 that they will require some modification when we pass to the 

 consideration of substances of greater solubility. Van't 

 Hoffj, in his illustration of the fact that q calculated and 

 observed gives satisfactory confirmation of his equation, 

 selected for this reason a number of substances of small 

 solubility and temperatures where the solubility was the 

 least. Le Chatelier further showed that from a consideration 



* Communicated by tlie Author, 

 t Studien zur chemischen Dynamik, p. -15. 

 Phil. Mag. S. 6. Vol. 5. No. '2S. April 1903. 2 E 



