THE NEW THEORY OF SOLUTIONS. 



171 



the vapour-pressure curve of the solution, and F' will corre- 

 spond to a temperature t which is the freezing-point of the 

 solution, for at F' the vapour-pressures of solution and solid 

 solvent are the same. It is evident from the diagram that 

 / is less than / ; consequently it follows from the fact that 

 the vapour-pressure of a solvent is diminished by the 

 presence of a dissolved substance that the freezing-point 

 is also diminished. The lowering of the freezing-point, 

 t' — t or AT, has been found to obey the following laws. 



Influence of concentration. — The freezing-points of in- 

 different solutions have only been investigated within com- 

 paratively recent times, although more than one hundred 

 years ago James Blagden communicated to the Royal 



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Society a series of observations on the freezing-points of 

 aqueous solutions of simple and mixed salts, and announced 

 the law, to which, however, there were exceptions, that the 

 lowering of the freezing-point of the solvent was propor- 

 tional to the amount of dissolved substance present in the 

 solution. In 1882 Raoult began to employ solvents other 

 than water. For solutions containing not more than 

 1 gram-molecule of substance in 1000 gr. of solvent, he 

 found Blagdeiis law to be approximately true. Subsequent 

 investigation by Raoult himself, and by other observers, 

 in particular the extensive measurements by Beckmann and 

 Eykman, have proved that, in general, even in dilute solu- 

 tions, Blagden's law is not strictly obeyed. If, as before, 



