SOLUTIONS 



179 



the freezing-point by the same number of degrees, and that 

 when equal quantities of different substances were dissolved 

 there was a simple relation of some kind among their molecular 

 weights. But it was only after a long series of experiments that 

 Raoult succeeded in establishing his important generalisations. 



When known quantities of the same substance are successively 

 dissolved in the same portion of a solvent on which it has no 

 chemical action, there is a progressive lowering of the freezing- 

 point of the solution, which is proportional to the weight of 

 substance dissolved in a constant weight of the solvent. But it 

 is not possible to carry the process very far, as deviations from 

 this rule occur when strong solutions are used. But the relation 

 of the depression produced by a small quantity of the substance 

 to its molecular weight enabled Raoult to arrive at an important 

 conclusion. 



The following are some of his experimental results : 



