[BARNES] DEPRESSION OF THE FREEZING-POINT 48 
The hammer (#) of an electric bell, covered with a piece of rubber 
tubing and supported on a frame over the freezing-point apparatus, was 
used for tapping the thermometer (7). A current from an Edison- 
Lalande cell had sufficient strength to give rapid and vigorous blows. 
The following method of Raoult’s' was employed for determining 
the elevation above the temperature of the protection bath, of the con- 
vergence temperature of this apparatus, 2.e., the temperature finally 
assumed by a solution which is being stirred and has no ice in it, when it 
comes into thermal equilibrium with the protection-bath. The freezing- 
point of water was first obtained. The ice formed in this observation 
was then melted and the freezing-tubes containing the water returned to 
the protection-bath and the stirring begun. With the protection-bath 
kept constantly at 0°, the temperature of the water in the freezing tubes 
at first fell rapidly, then more slowly, till it remained constant at about 
0-04°. This experiment was repeated with solutions of electrolytes 
giving the same result, and thus the convergence temperature was shown 
to be 0-04 degree above the temperature of the protection-bath. In all 
experiments, therefore, the temperature of the protection-bath was ad- 
justed so as to be 0-04 degree below the freezing-point of the solution. 
It was also found with water that the protection-bath required to be this 
same amount (0-04 degree) below the freezing-point, in order that the 
value of the freezing-point, with a very small quantity of ice present, 
might agree with that obtained with a large amount of ice. 
The method of carrying out an observation of the freezing-point was 
as follows: The inner freezing tube was filled up to a mark on the glass 
with the solution at about 0°, the thermometer and cork brought into 
position and the inner tube placed in the outer. These tubes were then 
brought into the freezing bath where they remained until the temperature 
was lowered with constant stirring to about 0:3 degree below the freezing- 
point of the solution, this point having been approximately determined by a 
preliminary experiment. Then the tubes were quickly removed to the 
protection bath which was at the required temperature (0°04 degree 
below the freezing-point of the solution), and the stirring started. After 
ten minutes time, in which the solution had risen to within 0-1 degree of 
its freezing-point, a small crystal of ice was introduced through a glass 
tube in the cork. As the particles of ice gradually formed throughout 
the solution the mercury in the thermometer gradually rose, and in 
about a minute assumed a fixed position. The tapping was then begun 
and continued for half a minute, when both it and the stirring were 
stopped, the microscope and incandescent lamp brought into position and 
a reading made, After again stirring and tapping, the thermometer was 
read again, this reading acting as a check upon the former. Care was 
taken to keep the protection-bath constant at the required tempera- 


1 Ztschr. f. phys. Chem. 27, 636, 1898. 
