In conclusion, it is my pleasant duty to express my sincere thanks 

 to the Board of Trustees of the Groningen University Fund and 

 to the Directors of the Utrecht Society for Science and Arts, who 

 by their support have rendered possible the publication of this 

 volume in its present form at such an unfavorable time; as well as 

 to the publisher for the care he has bestowed on the printing, and 

 the attractive garb he has given to the book. 



F. M. JAEGER. 

 Groningen, Holland, May 1917. 



Laboratory for Inorganic and Physical Chemistry 

 of the University. 



