146 ON THE DEPRESSION OF THE FREEZING-POINT 
protection bath was of thick brass wire with two rings, one for 
the upper aud the other for the lower portion. Both these 
stirrers were worked mechanically by means of one of Henrici’s 
hot air motors placed at a distance of about 3 metres from the 
freezing-point apparatus. By means of a light belt this motor 
turned a small wooden wheel placed over the protection bath, 
A connecting-rod connected this wheel to a slider on a vertical 
guiding rod; and to this slider also were attached the two 
stirrers. Any range of stroke could be obtained by varying the 
distance of the connecting-rod from the centre of the wheel. 
As about 70 cc. of solution were used,a stroke of 11 cm. was 
required to cause the ring of the stirrer in the freezing-tube just 
to touch the bottom of the tube and reach to within 4 em. of 
the surface of the solution. Thus all solutions were throughout 
uniformly stirred, and as the stroke of the engine was quite 
constant every solution was stirred in exactly the same manner. 
Another glass vessel of the same dimensions as the protection 
bath contained salt water and ice at a temperature of about 
— 10°C. (called the freezing bath). The purpose of this bath 
was to reduce the solution in the freezing-tube to about 0.3 
degree below the freezing-point. 
The hammer of a common 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. A 
current from an Edison-Lalande cell had sufficient strength to 
give rapid and vigorous blows. 
The following method of 1 Raoult’s was employed for deter- 
mining the elevation above the temperature of the protection 
bath, of the convergence temperature of this apparatus, 7. 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 
1 Ztschr. f. Phys. Chem., 27, 636, 1898, 
