122 REPORTS ON THE STATE OF SCIENCE.—1912. 
The third component, H*, OH’, or HX, may exert its influence by 
forming a reacting ionic or non-ionised complex with one or other of the 
two reagents. 
In aqueous solution the choice lies between (i), (ii), or (iv). Strong 
acids have a feeble, whilst bases and even such a slightly hydrolysed 
salt as sodium acetate have a powerful, catalytic effect. These relations 
suggest that in aqueous solutions hydroxyl ions play the predominant 
part. In that case traces of acids by decreasing the concentration of 
the hydroxyl ion should have a great retarding influence. It is true 
that acetic acid does slightly retard the hydrolysis, but we have not 
found any such effect with sulphuric. Hence, although hydroxyl ions 
are powerful catalysts, it may be concluded that in pure water the 
hydrolysis mainly follows equation (i) and is non-catalytic. 
In relatively anhydrous media, reaction (ili) obviously predominates. 
The reaction is very slow in the absence of acids; molecular quantities 
of acids are equally effective, and the speed is a linear function of the 
concentration of the acid. 
In media such as 50 per cent. acetic acid or acetone, the catalytic 
effect is now due to the hydrogen ions (equation ii) for equivalent quan- 
tities of acids are now of equal influence; but inasmuch as the rate of 
hydrolysis is considerable in the absence of an acid catalyst, the reaction 
also follows equation (1). 
In media with less than 50 per cent. of water the catalvtic effect of 
acids follows both equations (ii) and (iii). 
It is worthy of note that the velocity factor of the reaction is not 
independent of the initial concentration of the acetic anhydride, the value 
falling as the initial concentration increases. This fact was observed 
and commented on by Rivett and Sidgwick, and is deducible from 
Lumiére and Barbier’s results for aqueous solution. In our measure- 
ments the same fact is obvious both in aqueous and in 80 per cent. acetic 
acid. Thus for the initial concentration 0°486 and 0°269 molecule the 
value of HK” is 0'074 and 0°084, respectively, in aqueous solution; in 
80 per cent. acetic acid, ki” is 0°0047 and 0°0056 for the initial con- 
centrations 0°1625 and 0°0813 molecule respectively. When log k 
is plotted against log c (the concentration) for a series of values of c (be- 
tween 0°1169 and 0°3947), selected from Rivett and Sidgwick’s measure- 
ments, approximately a straight line is obtained. Burke and Donnan °® 
have observed a similar phenomenon in the reaction of silver nitrate and 
alkyl iodides, except that that value of k increases with increase of the 
concentration (of the silver nitrate). Here also log k& and log ¢ are 
linearly related, and hence the variation is expressed by the exponential 
law, k = Ke". 
III. Some Properties of Acetic Anhydride. 
(With Marian Jonzs, B.Sc.) 
Both our own experience and a study of the literature show that the 
complete separation of acetic acid and acetic anhydride, and hence the 
_preparation of pure acetic anhydride is no simple matter. Fractionation 
9 Trans. Chem. Soc., 1904, 85, 555. 
