680 PRINCIPLES OF CHEMISTRY 



of potassium, rubidium, and csesium sparingly soluble, and the greater 

 the atomic weight of the metal the less soluble is the salt. In other 

 cases the reverse is observed the greater the atomic weight the more 

 soluble are the corresponding salts. The variation of properties with 

 the variation in atomic weights even shows itself in the metals them- 

 selves ; thus lithium volatilises with difficulty, whilst sodium is obtained 

 by distillation, potassium volatilises more, easily than sodium, and 

 rubidium and csesium as we have seen, are still more volatile. 



