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 was 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 
-3°C. 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. Ifthe 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 
* Ztschr. f. phys. chem., 27 643, 1899. 
