AUTHOR'S PREFACE TO THE ENGLISH TRANSLATION 



It was not without hesitation that I yielded to the urging of my 

 American friends and of the pubhshers in consenting to have this 

 monograph appear in an Enghsh translation, for a number of signifi- 

 cant advances have been made in this field since the appearance of 

 the original German edition. I finally decided to make at least par- 

 tial amends by pointing out in a number of addenda within the text 

 the most significant of these recent advances in our science. It is 

 hoped that these will suffice to call the reader's attention to them and 

 to direct him to the original sources for further details and study. 

 The subjects which are especially noted in these addenda are: the 

 recent contributions to the activity theory of ionization by G. N, 

 Lewis, Bjerrum, and Debye; the modification of the theory concern- 

 ing the dissociation of the ampholytes by Bjerrum; the theory of 

 oxidation-reduction potentials. The latter is sufficiently developed 

 in the new text to give the reader a basis for understanding the appli- 

 cation of this theory to the use of the quinhydrone electrode, and to 

 prepare him for the more recent studies in this field, particularly those 

 of W. M. Clark. 



I wish to express my gratitude to Dr. W. A. Perlzweig for his 

 painstaking and careful work on this translation. 



L. MiCHAELIS. 



Baltimore, June 1926. 



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