372 
Proceedings of Royal Society of Edinburgh. [sess. 
examined, the apparent lowering of the freezing point will he too 
great by 0*0003° if the room temperature is taken at 15°. This 
value was obtained from direct experiment with an exposed stem 
of 4°. The above error is only of importance however where 
absolute values of the freezing-point depressions are desired. Tor 
relative values even on different days it is only the variation of 
this error caused by change of the room temperature that concerns 
us. Since the extreme variation of the room temperature during 
the whole course of our experiments was only 3°, this source of 
error falls out of account. 
The effect of pressure on the reading of our thermometer was 
unusually small, being considerably less than 0*0001° for 1 mm. of 
mercury. 
Since in each case the thermometer was in the same position 
with regard to the vessel, the pressure under which the freezing 
point of the solution was measured was somewhat higher than the 
pressure under which the freezing point of water was observed, the 
vessel in the former case containing more liquid. The maximum 
error from this source, however, was only 0*000 15°, by which the 
depression would be too small. On only one day was the change 
in* the atmospheric pressure sufficiently great to affect the freezing- 
point depression perceptibly. 
The zero of our thermometer when in use varied very regularly. 
In no case did the zero change by as much as 0*001° in twenty-four 
hours. The maximum difference observed between the zero taken 
in the morning experiment and that taken in the afternoon was 
0*0003°, except on one occasion, when the thermometer accidentally 
received a sharp blow on the bulb, when the zero was found to have 
suddenly changed by 0*002°. 
Convergence temperature . — The convergence temperature in our 
apparatus was found to be about +0*04°, the temperature of the 
external bath being 0°. The maximum freezing-point depression 
which we observed was 0*19°, so that in the most unfavourable 
case the equilibrium temperature was 0*23° below the convergence 
temperature. By direct experiment we found that at — 0*25° the 
liquid in the Dewar vessel gained 0*16 gram-calories per minute, 
i.e ., enough heat to melt 2 milligrams of ice per minute or 0*12 
grams per hour. Since the quantity of solution employed was 120 
