428 DETERMINATION OF THE FREEZING-POINT DEPRESSIONS 



thoroughly cleaned and rinsed with the solution. The inner 

 freezing-tube was then filled up to a mark on its side this mark 

 being about 2mm. above the highest position reached by the 

 stirrer. The cork bearing the thermometer wa= put in its place, 

 the tubes were then placed in a mixture cf snow and salt, and 

 the solution kept continually stirred until its temperature fell to 

 3C. below its freezing-point. They were then placed in position 

 in the protection bath, and the stirring was begun. When the 

 mercury, which rose very slowly, arrived at .1 degree below the 

 freezing-point, an ice-crystal was introduced through the holes 

 in the corks. After the mercury became stationary, the tapping 

 of the electric hammer was begun and lasted for half a minute. 

 The stirring was then stopped, the light put into position, and a 

 reading made with the microscope. The stirring was then begun 

 again and after a few minutes a second reading made. With my 

 apparatus, I found no difficulty whatever in getting the mercury 

 to remain stationary for at least five minutes. In cases where 

 more than one observation was made on the same solution, the 

 mean value was taken. As it was only the depressions that I 

 wanted, I found the freezing-point of water immediately before 

 or immediately after the above determination. The water used 

 was of the same degree of purity as that used in making up the 

 solutions. Other conditions, such as the introduction of the ice- 

 crystal, were kept the same in both cases. If the barometer was 

 varying rapidly, the freezing-point of water was taken immedi- 

 ately before and after that of the solution, and the mean taken. 



The depression is the difference between the freezing-point 

 of water and that of the solution under consideration. I found 

 by experiments performed on different days, that of a series of 

 depressions, a single value varied from the mean value by not 

 more than .0005 degree. As this would be large for dilute 

 solutions, I was unable to deal with solutions of greater dilution 

 than I have used. 



To correct for the change in concentration, due to the intro- 

 duction of an ice-crystal .1 degree below the freezing-point, I 

 made use of Raoult's method* for determining the depression 



Ztechr. f. phys. chem., 27 6i3, 1899. 



