FREEZING-POINT METHOD. 7 



SOLUTIONS. 



The method of preparing the solutions varied somewhat according to 

 the substance employed, but, in general, it may be said that a solution of 

 two or three gram-molecular weights to the liter was first made, and from 

 this, by successive dilutions, the less concentrated solutions were obtained. 

 Wherever possible the mother-solution was made up by direct weighing. 

 When this was not the case the solution was standardized either by gravi- 

 metric or volumetric methods. Great care was taken to insure the accurate 

 standardization of the mother-solution, and the dilutions were made with 

 volumes large enough to minimize errors in burette readings and flask 

 adjustments. 



The water that was used as solvent was of a high degree of purity. The 

 ordinary tap-water was first distilled in the laboratory still, and then redis- 

 tilled from a dilute solution of chromic acid. This second distillate was 

 then distilled a third time according to the method of Jones and Mackay.* 

 The water thus obtained was preserved in a large bottle which had previously 

 been subjected to careful cleaning. The water showed an average conduc- 

 tivity of l.OxlQ- 6 - 



METHODS. 



FREEZING-POINT METHOD. 



The practical details of the freezing-point method may be set forth most 

 clearly by a description of the determination of the freezing-point of water, 

 by which the zero-point of the thermometer was established, prior to making 

 any measurements with solutions. 



The freezing-tube was filled to a depth of 5 cm. with pure distilled water, 

 and the thermometer and stirrer inserted. The tube was then placed in a 

 vessel containing ice and salt, and the stirrer agitated frequently until 

 ice separated. The tube was then removed and warmed until the ice just 

 melted. It was then placed in the freezing- jacket, which was surrounded 

 with finely crushed, dry ice, to which had been added just enough salt to 

 bring the temperature of the mixture a few degrees below the freezing-point 

 of the solvent. 



The stirrer was agitated from time to time until freezing began, when 

 the stirring was continued vigorously, and at the same time the electrical 

 hammer was set in action. The thermometer scale was illuminated by the 

 incandescent lamp, and the reading taken after the mercury column had 

 remained stationary for about thirty seconds. It was almost always found 

 that the solvent undercooled several degrees, and it was frequently neces- 

 sary to add a small fragment of ice to induce freezing. 



*Amer. Chem. Journ., 19, 83 (1897). 



