106 REPORTS ON THE STATE OF SCIENCE. 
A most excellent method has now been devised for determining the 
amount of unchanged aniline. This consists in stopping the reaction 
‘by adding anhydrous sodium acetate, equivalent to the acid catalyst, 
followed by some excess of an acetic acid solution of nitric acid. The 
aniline is rapidly and quantitatively converted into a nitroamine 
(Ortont; W. H. Gray*). The nitroamine is completely extracted 
from the diluted solution by shaking three times with chloroform, and 
its quantity measured by titration of its alcoholic solution with baryta. 
The composition of the system could also be checked by direct, estima- 
tion of the remaining acetic anhydride by the method devised by Orton 
and M. G. Edwards,* and amplified by Orton and Marian Jones.” 
The amount of anhydride found at a given period of the reaction corre- 
sponded well with that calculated from the initial concentration on 
the assumption that the loss of anhydride was solely due to acetylation. 
The accuracy and the refinements of this method of analysing the 
system are mainly due to the exhaustive experiments of Mr. W. H. 
Gray ® on the stability of nitric acid in acetic acid ‘solution and allied 
problems. The error in the estimation of the nitroamine in an acetic 
acid solution is not above + per cent., whilst the error in the determina- 
tion of the aniline by conversion into nitroamine falls below 1 per cent. 
The velocity coefficients for a reaction of the second order are re- 
markably constant, in spite of the canteens and intricate analyses 
by which they are obtained. 
Illustrations of the results are given in the following table :— 
Exp. A. Initial concentrations :—s- tribromoaniline, 0°04; acetic anhy- 
dride 0°04 x 3°83; H,SO,=M/363°8.  ~ 
Percentage aniline 
Time from mixing. acetylated. Kn. 
Min. 
41 17-52 0-031 
86 31:5 0-030 
146 48-14 0:031 
240 69-92 0-037 
Exp. B. s-tribromoaniline, 0°02; acetic anhydride, 0°02 x 7:08; 
H,SO,=M/363'8. 
Min. . 
66 38:19 0-053 
157 69-65 0-069 
283 90-05 0-064. 
Exp. C.  s-fribromoaniline, 0°02; acetic anhydride, 0:02 x 7:08; 
11,80,=M/727°6. 
Min. 
40 17-25 0-032 
87 28-55 0-026 
142 40:3 0-025 
240 61:3 0-028 
Since in the presence of sulphuric acid the anhydride is immediately 
4 Trans. Chem. Soc. 1902, 81, 490. 
5 Thesis submitted to the University of Wales, 1914. 
6 Trans. Chem. Soc. 1911, 99, 1181. 
7 Trans. Chem. Soc. 1912, 101, 1716. 
8 Loc. cit., and Analyst, 1912, 37, 303. 
