vi PREFACE 



Professor F. G. Donnan, of the University of London, an- 

 nounced in 1910 an ingenious theory of equilibria which are 

 established when two solutions of electrolytes are separated by a 

 membrane which is permeable to all except one ion. This theory 

 was successfully applied by Procter and Wilson to the explana- 

 tion of the influence of electrolytes on the swelling of gelatin. It 

 will be shown in this volume that Donnan's theory of membrane 

 equilibria furnishes a quantitative and mathematical explanation 

 not only of swelling but of the colloidal behavior of protein solu- 

 tions in general ; namely, electrical charges, osmotic pressure, vis- 

 cosity, and stability of suspensions. Such an application of 

 Donnan's theory would have been impossible without the stoichio- 

 metrical proof that proteins form true ionizable salts with acids 

 and alkalies. What was at first believed to be a new type of chem- 

 istry, namely colloid chemistry, with laws different from those of 

 general chemistry, now seems to have been only an unrecognized 

 equilibrium condition of classical chemistry; at least as far as 

 the proteins are concerned. This does not detract from the 

 importance of colloidal behavior for physiological and technical 

 problems, but it completely changes the theoretical treatment of 

 the subject. 



Any rival theory which is intended to replace the Donnan theory 

 must be able to accomplish at least as much as the Donnan 

 theory, i.e., it must give a quantitative, mathematical, and 

 rationalistic explanation of the curves expressing the influence 

 of hydrogen ion concentration, valency of ions, and concentration 

 of electrolytes on colloidal behavior; and it must explain these 

 curves not for one property alone but for all the properties, 

 electrical charges, osmotic pressure, swelling, viscosity, and 

 stability of solution, since all these properties are affected by 

 electrolytes in a similar way. 



The contents of the book are divided into two parts, one fur- 

 nishing the proof of the stoichiometrical character of the reactions 

 of proteins, the second developing a mathematical and quantita- 

 tive theory of colloidal behavior on the basis of Donnan's theory 

 of membrane equilibria. 



The theory of colloidal behavior, as outlined in this book, can 

 only be considered as a first approximation. Finer methods of 

 experimentation will have to be introduced, many minor dis- 



