160 PROCEEDINGS OF SECTION B. 
NOTE ON EMPLOYMENT OF RAOULT’S METHOD 
FOR MOLECULAR WEIGHT DETERMINATION 
IN ELEMENTARY SCIENCE CLASSES. 
By Prof. EasterFieLp, M.A., Ph.D., and Jamzs Bes, M.A. 
[A bstract.] 
THE cryoscopic method is one of the most rapid of the 
many methods for the approximate determination of mole- 
cular weight. The necessity for employing delicate ther- 
mometers has, however, been generally held as deterrent 
to the employment of the method amongst elementary 
students. 
It is, however, evident that if, in applying the well-known 
w x 100 
formula,— D=K Sx M 
(in which D = observed depression; M = mol. weight 
sought; W = weight of dissolved solid; S = weight of sol- 
vent; K = a constant for the particular solvent), the 
depression might be measured on a common thermometer 
if a solvent were taken with a high depression constant and 
the dissolved substanee were of sufficiently low molecular 
weight. Thus, the molecular weight of water is 18, the 
constant for phenol 72°,sothat 1 per cent. of water depresses 
the m.p. of phenol nearly 4°, and since degrees on a com- 
mon thermometer can easily be assessed to fifths, good 
values can be obtained with the simplest apparatus, viz., 
common thermometer, brass-wire stirrer, and test tube. It 
is important in the case of water in phenol that the con- 
centration shall not exceed 1-5 per cent, since at higher 
concentration molecular association takes place with extra- 
ordinary rapidity. 
