POTASSIUM, RUBIDIUM, AND CESIUM. 25 



In conclusion, the authors acknowledge with pleasure their indebtedness 

 to the Carnegie Institution of Washington for the pecuniary aid which 

 made this research possible. 



SUMMARY. 



The compressibilities of the alkali metals were successfully studied by 

 the new method of Richards and Stull, slightly altered to suit the new 

 conditions. The pressure being expressed in megabars, they were found 

 to be : 0.0000088 for lithium, 0.0000154 for sodium, 0.0000315 for potas- 

 sium, 0.00004 for rubidium, and 0.000061 for caesium, between pressures 

 of 100 and 500 megabars. 



These numbers are almost proportional to the respective atomic volumes. 



The greater the compressibility, the greater was found to be its decrease 

 with increasing pressure. 



