FREEZING-POINT APPARATUS. 



the ring was such that when wrapped with the smaller wire, it would just 

 touch the walls of the freezing-tube, and thus hinder the formation of an ice- 

 sheath. This device was found to give perfect satisfaction, and to be in 

 every sense superior to the ordinary glass stirrer. The platinum stirrer was 

 attached to a glass rod, which passed closely through a glass tube in the cork 

 of the freezing-tube. In this way the movement of the stirrer was guided, 

 and cramping prevented. 



The freezing-tube consisted of a large test-tube of 80 cc. capacity, sur- 

 rounded by a second glass tube, giving an air space between the two of about 

 a centimeter. This outer tube was 

 surrounded by the freezing mixture, 

 which was contained in a large bat- 

 tery-jar wrapped with felt to diminish 

 radiation. The freezing mixture was 

 varied to suit the conditions, the solu- 

 tions of lower concentrations freezing 

 with a mixture of salt and ice, while 

 those of greater concentrations often 

 required the use of crystallized calcium 

 chloride and ice. 



By means of a small electric ham- 

 mer, uniform and gentle blows were 

 delivered on the top of the thermome- 

 ter during the time of an observation, 

 thus overcoming the friction of the 

 mercury in the capillary. 



To facilitate the reading of the 

 thermometer, a small lens magnifying 

 several diameters was employed, and 



FIG. 1. 



more intense illumination of the thermometer scale was obtained by means 

 of a small incandescent lamp. A thermometer graduated to tenths served 

 to indicate the temperature of the freezing mixture, the effort being made 

 to keep this only a few degrees lower than the freezing temperature of the 

 solution under observation. 



CONDUCTIVITY APPARATUS. 



The conductivity measurements were made by the well-known Kohl- 

 rausch method, using the Wheatstone bridge, inductorium, and telephone. 

 Two types of cells were used. For the more dilute solutions the ordinary 



