POTASSIUM, RUBIDIUM, AND CESIUM. 



1.2 



I.I 



1.0 

 0.9 



0.8 

 0.7 



0.6 



0.5 

 0.4 



0.3 

 0.2 

 0.1 



A 



100 



200 



300 



400 



500 



600 



Fig. 4. Type of Plot for Calculation. 

 A, Mercury. B, Sodium. C, Oil. 



Having thus either clean bars of metal, or glass tubes containing bright 

 metal and oil, the determination of the compressibility was a simple matter. 

 The bars were immersed in oil and the tubes were immersed in mercury in 

 the glass jacket; and each was compressed with weighed additions or 

 removals of mercury as before. The results are given in the table. 



The pressure interval from 100 to 500 kg. per square centimeter was 

 used throughout the calculation of the results. Later a table is given show- 

 ing in some cases the values of the compressibilities for shorter intervals, 

 but these can not claim great accuracy. The calculation may be performed 

 with the help of the equation given in the previous paper; but it is more 

 simply performed in this special case in the following manner: 



In the first place, the difference between the weight of mercury added for 

 400 kg. per square centimeter when the oil and alkali metal were in the 



