FREEZING-POINT APPARATUS. 177 



the solutions which come in contact with it. The foil was selected as thin 

 as was consistent with rigidity, so as to produce as narrow a band of separa- 

 tion between the two transmitted portions of the main incident-beam as 

 possible. With this same object in view, the least bit of cement was used 

 to make the lower surfaces of the glass ends of the upper compartment 

 adhere to the platinum. The two boxes were made separate and distinct, 

 so as to facilitate washing, drying, etc. The lower compartment was made 

 wider than the upper, so that when the latter was resting in position on top 

 of the former it was a simple matter to pour a given solution into the lower 

 compartment until it came into contact with, and wet the entire under 

 surface of the platinum. Consequently, the liquids were as close together 

 as the thickness of the platinum (0.061 mm.), and their spectra appeared 

 sufficiently close together in the field of view of the telescope to admit of 

 accurate and easy comparisons. 



A suitable stand for this apparatus was fitted with leveling screws, which 

 enabled the experimenter to adjust the cell so that the plane of the plati- 

 num partition contained the axis of the incident-beam, at the same time 

 that the ends of the cell were perpendicular to this line. 



FREEZING-POINT APPARATUS. 



This system was of the improved Beckmann type, which can be found 

 described in so many places that mere reference to it here is quite sufficient. 

 The thermometer used with this apparatus was also of the Beckmann type. 

 The smallest spaces on the stem of the thermometer signified 0.02 C., and 

 the total range of scale was 12. 



For temperatures lower than 10 or 11 below zero, two alcohol thermom- 

 eters were employed. These instruments are graduated in one-half degrees, 

 and the lowest temperatures which they could register were, respectively, 

 55 and 82.5 below the standard freezing-point of water. 



With the Beckmann apparatus a mixture of ice, water, and sodium chlo- 

 ride was used as the refrigerating agent. With the alcohol thermometers 

 a suitable mixture of solid carbon dioxide and ethyl alcohol was employed. 



CONDUCTIVITY APPARATUS. 



The usual combination of a Wheatstone slide-bridge, with a small induc- 

 tion coil and telephone receiver, was used. The conductivity cell was of 

 the U-tube pattern,* since most of the solutions were too concentrated to 

 give sharp tone minima in cells of less ohmic resistance. All of the measure- 

 ments for this system were made at zero degrees. All necessary precautions 

 were taken to obtain reliable data. 



* Jones and Getman: Ztschr. phys. Chera., 49, 389 (1904). 



