Identification of Organic Compounds. 45 



mercury on the thermometer scale is noted. The con- 

 denser of the tube A is then removed, a weighed amount 

 of the substance (w) under investigation (compressed, when 

 a solid, into a pastille) is added through the side tube, and 

 the condenser is then rapidly replaced. The solution of 

 this substance will raise the boiling point of the solvent 

 (after a momentary fall), and the mercury in the column 

 will finally rise. As soon as its position has become 

 constant, it is noted. The difference between this and that 

 of the pure solvent will give the elevation of the boiling 

 point e produced by dissolving W grammes of the substance 

 under investigation in w grammes of solvent. If 1c is the 

 molecular elevation of the solvent (that is, the theoretical rise 

 produced when a gramme molecular equivalent of a sub- 

 stance is dissolved in 100 grammes of the solvent, as 

 calculated by measuring the rise produced by the solution 

 of a given weight of a solute of known molecular weight 

 in a given weight of the solvent), then m, the molecular 

 weight, can be calculated from the formula 



m = k- X 100. 



