120 REPORTS ON THE STATE OF SCIENCE.—1912. 
As the acetic acid is diluted, the rate of hydrolysis increases roughly 
proportionally to the amount of water in the medium. It is remarkable 
that pure acetic anhydride should be such a curiously unfavourable 
medium for its own reaction with water. 
(iii) Effect of Catalysts.—In aqueous solution alkalis are very power- 
ful catalysts of the hydrolysis. Acids have, on the other hand, but a 
very feeble effect. Such slightly hydrolysed salts as sodium acetate 
occupy an intermediate position. 
In anhydrous media acids produce a great acceleration of the 
reaction, but the effect diminishes as the proportion of water in the 
medium decreases. 
Tasce III. 
. Concentration) Concentra- /Tempera-| Speed of Hydro- / 
Medium | of HeSO4 | tionof Ac,O} ture lysis | 
~ — — — - | zx — | | 
Glacial acetic acid . . — 00804 | 16 12% in 24 hrs. | 
ky:=0°00042 | 
0:002M — 0-077 16 52% in 10 mins. 
90 per cent. acetic acid — 00815 16 k, =0-0028 
0-0166M@ | 0:0807 16 0-016 
01M | 0-091 15 0-076 
50 per cent. acetic acid — 0083 , 15 0-016 | 
| 0:034M = 00835 15 0:03 
With regard to the nature and concentration of the acid, it is to be 
noted that :— 
(i) In 90 and 95 per cent. acetic acid molecular quantities of acids 
are equivalent in accelerating effect. 
(ii) In 50 per cent. acetic acid equivalent quantities of acids produce 
equal effects. 
(iii) At intermediate compositions of the medium there is no simple 
relation. 
(iv) When the effect can be measured as in 90 per cent. acetic acid, 
the rate of hydrolysis is found to he proportional to the concentration of 
the catalyst. 
These relations indicate that the unionised acid is the effective 
catalyst in media containing 90 per cent. acetic acid and upwards, but 
that the ionised acid is the catalyst in media containing 50 per cent. 
acetic acid. 
Nitric Acid as Catalyst.—In its relation to the hydrolysis of acetic 
anhydride, nitric acid occupies a unique position. Whilst in 50 per cent. 
acetic acid its effectiveness is identical with that of other acids; as the 
proportion of water in the medium decreases, its relative activity steadily 
falls off, until in glacial acetic acid it is, compared with sulphuric acid, 
infinitesimal, 
