OF ARTS AND SCIENCES. 247 



this point can be settled only by a new series of observations with a 

 more accurate method. If this is assumed to be true, the mean of the 

 numbers given in the meta column will represent the rate at which 

 the metabrombenzylbromide is attacked, in comparison with that for 

 the para compound taken as 100. This mean is 77; that is, about 

 three quarters as much bromine is removed from the meta as from the 

 para compound in the same length of time. 



The numbers given in the ortho column show much more serious 

 deviations, the maximum difference amounting to twenty per cent ; 

 but, as I observed that these numbers increased essentially with the 

 time during which the specimen had stood exposed to the air of a 

 desiccator, the experiments having been tried in the following order, — 

 10 minutes, 55 % ; 5 minutes, 64 % ; 20 minutes, 58 % ; 30 minutes, 

 75 %, — I was led to the conclusion that the substance was undergo- 

 ing decomposition, which afterwards was proved to be tlie case by the 

 following analyses : I. made before, II. and III. after, the series of 

 experiments. 



I. 0.2375 grm. of orthobrombenzylbromide gave, by the method 



of Carius, 0.3565 grm. AgBr. 

 II. 0.2950 grm. of substance gave 0.3705 grm. AgBr. 

 III. 0.4100 grm. of substance gave 0.5210 grm. AgBr. 



Calculated for CjHgBrj. 



Bromine 64.00 



The complete study of this decomposition must be postponed till a 

 future paper. I can only say here, that no appreciable amount of 

 free hydrobromic acid could be detected in the substance analyzed 

 above, and that I have often found crystals of orthobrombenzoic acid 

 in specimens of orthobrombenzylbromide which had stood exposed to 

 dry air for several months. Whatever may be the nature of the 

 change, it is evident that the ortho numbers are of no value ; and no 

 attempt was made to correct them by new experiments, because such 

 an unstable substance as the orthobrombenzylbromide is entirely unlit 

 for work of this sort. 



I will add a number of other comparisons, which were made by less 

 accurate processes during the elaboration of the method. They are 

 given as in Table II., the amount of bromine removed from the para 



* As tliese experiments were made before the orthobrombenzylbromide was 

 obtained in the solid state, 1 had no criterion of its purity except the analysis. 



