12 



THE PROPERTIES OF SOLUTIONS. 



[CH. I. 



The precipitation is greatest in tube 5. 



The concentration of hydrogen ions (see p. 19) can be calculated 

 approximately from the following formula, no allowance being made 

 for the acidity of the casein. 



. K (acetic acid in mols. per litre) 

 a (sodium acetate mols. per litre) 

 (H) = Hydrogen ions in grams per litre. 

 K = dissociation constant of acetic acid = 1-85 x io~ 5 . 



a = dissociation constant of sodium acetate. 0-87 for o-oi N. 



0-79 for o-i N. 



The theoretical basis for the formula is given on p. 19. 

 Thus in tube 5, 



(H) = 1-85 x io- 5 x io- 2 



_ = 2-13 x io~ 5 . 



0-87 x io~ 2 



Below are the (H) and PH (see p. 16) of the various tubes. 



Still finer adjustments of the reaction can be obtained by suit- 

 ably varying the concentration of acetic acid. The (H) can be 

 calculated from the formula. 



