3«2 



SCIENCE PROGRESS. 



Such is the theory of concentrated solutions which evi- 

 dently goes some way to explain the facts illustrated by the 

 preceding examples. These show that, in general, the 

 properties of strong solutions deviate from those of ideal 

 solutions just as the properties of compressed gases deviate 

 from those of gases at small concentrations ; and further, 

 that the deviations are if anything less marked in the 

 former case, when the comparison is made under conditions 

 which according to the gaseous analogy are similar. 



ASSOCIATED SOLUTIONS. 



Molecular weights in associated solutions. — -To this 

 general rule there exists a well-marked series of exceptions, 

 which are comprised under the heading of associated solu- 

 tions. The peculiarities of these solutions have mainly been 

 brought to light by determinations of the freezing-point and 

 boiling-point, and were discovered by Raoult. The large 

 number of measurements of the molecular lowering of the 

 freezing-point, published by him in 1884, proved that in 

 solvents such as water, formic acid, and acetic acid, all in- 

 different substances gave what he termed " normal " values; 

 but they also showed that certain compounds, like the fatty 

 alcohols, the fatty acids, etc., when dissolved in solvents 

 like benzene, nitrobenzene, or ethylene dibromide, gave 

 lowerings which were abnormally small. Here are some 

 of the molecular lowerings he obtained calculated from the 

 theoretical molecular w T eights by the formula M'AT/^-. 



The " normal " value for benzene was 49, hence Raoult 

 came to the conclusion that hydroxy-compounds when dis- 



