Chemical Activity of Free and Semi-Combined Water. 133 



Orton and M. Jones, in addition to studying the velocity of hydrolysis 

 of acetic anhydride in acetic acid and water, investigated the effect 

 of catalysts. It was found that acids are powerful catalysts of the 

 hydrolysis. The effect is most noticeable in media containing but 

 little water, and diminishes as the proportion of the water increases, 

 being least obvious in pure water. The value of the velocity factor is 

 a linear function of the concentration of the acid. Alkalis and hydro- 

 lyzed salts were also found to act as strong catalysts of the hydrolysis 

 in aqueous solutions. The following equations were given to represent 

 the mechanism of the hydrolysis: 



(I) AC 2 0+H,O = 

 (II) AC 2 0+HoO+H+ = 



(III) ACoO+HoO-hHX=2AcOH+HX 



(IV) AC 2 + H 2 + OH = 2AcOH+OH 



Any one of the four forms could predominate, according to the con- 

 ditions, medium, etc. In aqueous solutions the choice lies between 



(I), (II), and (IV). 



HYDROLYSIS OF SALTS. 



It is a well-known fact that certain salts, even though they contain 

 the strictly equivalent quantities of acid and base required for "neu- 

 trality," when dissolved in water are not neutral to indicators, but 

 react either acid or alkaline. This was first noticed by H. Rose, in 

 working with certain basic salts, but was not explained satisfactorily 

 until Arrhenius proposed his theory of electrolytic dissociation. In the 

 light of this theory acidity is due to the presence of an excess of hydro- 

 gen ions, while alkalinity is due to the presence of an excess of hydroxyl 

 ions. These ions can not be accounted for by the salts themselves; 

 therefore they must be accounted for by the water. 



Water must contain both hydrogen and hydroxyl ions. The ioniza- 

 tion constant of water can be calculated by the equation 



H+XOH- 

 H 2 



Since the active mass of the nonionized water is so great in comparison 

 with the active mass of the ions, it may be considered constant. We 

 then have H + XOH- = fc H 2 O, the value oik being 1.2X10-14 at 25. 

 This ionization is the same in all aqueous solutions. The value 

 A- H2 o, however, increases with rise in temperature. This increase is 

 mcst prcbably due to the breaking down of the associated molecules 

 into the simpler ones, which are more easily dissociated. Pure water 

 contains an equal nvmber of hydrogen and hydroxyl ions, and there- 

 fore must react neutral. Furthermore, this relation holds for any 

 neutral solution. To be acidic, a solution must contain an excess of 



