208 



PROCEEDINGS OF THE AMERICAN ACADEMY 



column, under each substance, the differences between the percentages 

 at each temperature, and at that which immediately .follows it, are 

 given. 



TABLE III. 



From this it appears that the bromine begins to enter the side-chain 

 in considerable quantity at about the boiling-point of toluol (111 ), 

 and that after this the amount of benzylbromide formed increases 

 with the temperature, although to a much smaller extent, with the 

 exception of parabromtoluol, which is probably due to defects in the 

 process; in fact, the difference between 81°-100° and 110°-114° is 

 greater than that between the latter temperature and the boiling-point 

 of the substance, except in the case of the single series of observations 

 on parachlortoluol. 



Some experiments with paraiodtoluol cannot be directly compared 

 with the preceding, because we could find no satisfactory way of 

 removing the iodine set free during the addition of the bromine, and 

 were therefore obliged to content ourselves with weighing the crys- 

 tals of paraiodbenzylbromide formed. >Ve found, under these condi- 

 tions, that below 100° no crystals were formed; at about 111°, 18 per 

 cent of the calculated amount was obtained; at 135°, 42 per cent ; at 

 175°, 54 per cent; at 200°, 51 per cent. The low percentages are 

 partly accounted for by the solubility of the paraiodbenzylbromide in 

 the oily secondary products. A similar series with parachlortoluol 

 gave below 100° no crystals; at 111 , 89 per cent of very impure 

 crystals (apparently nearly one half parachlortoluol); at 135°, 98 per 

 cent of purer crystals ; at 1G0°, 89 per cent. These results confirm, in 

 a general way, those obtained by the more accurate method. 



Tltc effect of differences in temperature on the rate at which the bro- 

 mine is taken up will be seen from the following table, in which the 



