32 



PHYSICAL CHEMISTRY 



Table of Osmotic Pressures in Atmospheres for Depression of the 



Freezing Point. 



The solution to be frozen is poured into a test tube having 

 a double bored cork. This tube is sometimes provided with a 

 side neck through which a small crystal of ice may be dropped 

 to start the freezing as soon as the temperature reaches the 

 freezing point and thus prevent undercooling. The test tube 

 is fitted into a larger test tube and the space between them left 

 full of air or filled with alcohol to prevent the condensation of 

 moisture which would obscure observation. The freezing mix- 

 ture is usually crushed ice or snow and salt, but this interferes 

 with observation, and ether through which air is sucked is prefer- 

 able. 



The determination of the freezing point is as follows. About 

 22 cc of the solution is poured into a test tube, and the bulb of 

 the thermometer and a platinum stirrer lowered into it through 

 separate holes in the stopper. The test tube is cooled nearly to 



