20 HYDROGEN ION CONCENTRATION 



(By kw the value of is understood, where H2O is 



[H2OJ 



assumed to be proportional to the partial pressure of the water- 

 vapor in an aqueous alcoholic solution.) In a unimolar alcoholic 

 solution, which contains 4.6 per cent alcohol, the value of kw is 

 not easily distinguishable from that of kw for pure water. 



For all "watery" phases in living tissues the usual value of k^ 

 (that of pure water) is assumed. This value, however, may not be 

 applied to such "lipoid" phases as cell membranes, nerve fibers, etc. 



It has been stated recently by R. Keller^^ that colloidal aqueous 

 solutions, especially those of proteins, have a distinctly smaller 

 dissociation constant than pure water. The reason why this highly 

 important problem has not been accurately solved long ago lies in 

 the technical difficulties of determining the dielectric constant in 

 such well conducting fluids as aqueous solutions. If Keller's state- 

 ment is confirmed, then it will have an important bearing upon the 

 calculation of dissociation constants and of ionic equilibria. The 

 quantitative estimation of these values will not be considered for 

 the time being. 



6. The influence of dissolved electrolytes upon the state of dis- 

 sociation of water 



An electrolyte dissolved in water breaks up more or less com- 

 pletely into its ions. If one of these ionic species is the H-ion, 

 then the concentration of the hydrogen ions of the water is in- 

 creased a certain number of times. But since equation (3) on page 

 12 must remain unclianged, it follows that the concentration of 

 OH-ions must decrease the same number of times. If the dissolved 

 electrolyte yields to the aqueous solution OH-ions then the exactly 

 reverse effect occurs. An electrolyte which yields only ions other 

 than H- or OH-ions has no effect on the dissociation of the water. 

 H-ions are given off by acids and acid salts; OH-ions are produced 

 by bases and basic salts; electrolytes which yield neither of these 

 are the true neutral salts, (as NaCl, for example). 



It follows, therefore, that while every aqueous solution must 

 contain H+ or OH" ions it may react either acid, neutral or alkaline. 

 A neutral solution is characterized by the fact that it contains equal 



" R. Keller, KoUoid-Zeitschr. 29, 193 (1921). 



