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 cm. 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 



- 10C. (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, i. 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. 



