10 PREFACE 



The appended laboratory work has been drawn from the 

 manual in use in my classes for the last five years. Much of 

 the material has, of course, been drawn from other manuals. 



I wish to acknowledge suggestions and corrections in the 

 laboratory directions from various colleagues, particularly Dr. 

 F. B. Kingsbury. I wish also to express my thanks to Dr. W. 

 H. Hunter, who kindly volunteered to read the manuscript of 

 the theoretical portion. 



C. J. V. PETTIBONE. 



Minneapolis, Minn. 



