28 MORRIS LOEB 



for normal pressure, and the boiling-point is, of course, 

 capable of most exact determination. The method has been 

 elaborated by Beckmann, 1 while the reader will remember 

 a recent paper by Wiley on this subject, which does not, how- 

 ever, give sufficient details, as Beckmann's paper had al- 

 ready been announced. 



The latter 's apparatus consists of a vessel of about 100 cc. 

 capacity, having a rounded bottom and three necks. Of these, 

 the central one connects with a Soxhlet condenser, the second 

 carries a Beckmann thermometer, whose bulb is completely 

 submerged, and the third neck serves for the introduction of 

 the substance. 



Steady boiling is assured by filling the vessel to a certain 

 height with beads or garnets, and by sealing platinum wires 

 into the bottom to promote conduction. The pure solvent is 

 first raised to the boiling-point, its temperature noted, and 

 the weighed substance is thereupon introduced. As soon as 

 the thermometer has become constant, the rise is noted; a 

 fresh quantity of substance may then be introduced, and 

 the observation repeated. The formula for the molecular 

 elevation of the boiling-point is precisely like that found by 

 van 't Hoff for the freezing-point, 



0.02 T 2 

 t = > 



W 



with the exception that here T means the boiling-point of the 

 pure liquid and W its heat of vaporization. The constant t 

 being found by calculation or experiment, whenever we deter- 

 mine that for p grams of substance to 100 grams of solvent 

 there is an elevation e, the molecular weight of the sub- 

 stance being M , 



M^ 

 e 



1 Z. physik. Chem. t, 532 (1880). 



