OF ARTS AND SCIENCES. 



209 



mean time needed to bromir equivalent weights of the substances for 

 each temperature is given. Jn calculating these means, the times of 

 several experiments were used, in which the amount of benzylbromide 

 was not determined ; mauy of them, therefore, depend on a much larger 

 number of observations than the mean amounts given in Table III. 



TABLE IV. 



Although the method of adding the bromine used by us made great 

 differences of rate, under the same conditions, possible, so that all these 

 results must be taken with some caution, it is evident that the rate 

 increases rapidly, and apparently regularly, with the temperature, 

 showing no especially large increase between 81°-100° and 110°-114°, 

 as was the case with the per cent. This rapid increase in the rate 

 suggests the following objection to the results obtained in studying 

 the effect of temperature on the amount of benzylbromide formed ; the 

 small percentages of benzylbromide obtained below 100° may have 

 been due to loss of bromine from running the experiment too fast, as 

 the secondary products were not studied ; and therefore it is possible 

 that they were the unaltered original substance, and not formed from 

 this by substitution of bromine in the ring ; this view is supported by 

 the larger per cent (72) obtained in Experiment I., where the time 

 was 45 minutes longer than in II. ; but, on the other hand, it is hardly 

 possible that nearly 5 grs. of bromine could have escaped without giv- 

 ing a perceptible color to about the same quantity of hydrobromic acid, 

 and great pains were taken in every experiment to regulate the addi- 

 tion of the bromine so that the escaping fumes should be perfectly 

 colorless. Even if the amounts of benzylbromide obtained below 

 100° are rejected on this account, our statement that there is a decided 

 change in the action at 111° still holds good, as in that case the time 

 necessary to take up the bromine below 100° must be greatly increased, 

 and therefore the differences in rate between 87°-100° and 110°- 

 114° would become as great in proportion to the differences between 

 vol. xv. (n. s. vii.) 14 



