124 



Dr. T. E. Thorpe on the 



[Dec. 16, 



the succeeding drops of bromine disappear with far less rapidity, a fact 

 which evidently indicates that the substitution of the first atom of bromine 

 is more easily effected than that of the second. After standing for about 

 forty-eight hours, the liquid was shaken with a dilute solution of caustic 

 soda, and then repeatedly washed with water, dried over calcium chloride, 

 and submitted to fractional distillation. 



The liquid commenced to boil at about 145°, and a comparatively large 

 quantity passed over between 150° aud 160° ; a still larger fraction distilled 

 over between 1 70° and 1 80° ; but the greater portion came over between 1 80° 

 and 190°, after which the temperature rapidly rose, and the residue in the 

 flask became nearly solid, owing to the formation of a mixture of metastyrol 

 and styrolbromide. Throughout the process of distillation large quantities 

 of hydrobromic acid were evolved, and the portion boiling between 150° 

 and 160° was found by the characteristic bromine reaction to consist mainly 

 of styrol, 



C 8 H 9 Br=C 8 H 8 +HBr. 

 An analysis of the portion boiling between 180°-190° showed it to contain 

 very nearly the theoretical amount of bromine calculated for 



C 8 H 9 Br. 



0*9742 grm. substance gave 0 95 1 0 grm. silver bromide, and 0'0082 

 grm. silver 



Found. Calculated. 

 Bromine 42*1%. 43*2%. 



This compound is very unstable ; on renewed distillation it invariably 

 commences to boil at about 140°, and unless the distillation is very rapidly 

 conducted, a large proportion is transformed into styrol and hydrobromic 

 acid. So easily is this decomposition effected, that on exposing 4 or 5 

 grms. of the liquid in a sealed tube to a temperature of about 200° for a 

 few minutes, it is almost entirely converted into metastyrol, and on open- 

 ing the tube torrents of hydrobromic acid are evolved. The formation of 

 styrol may, however, be almost entirely avoided by conducting the distil- 

 lation in a partial vacuum ; and for this purpose the water-pump of Bunsen 

 may be very conveniently applied. The accompanying figure shows the 

 disposition of the apparatus employed for this purpose ; as it may here- 

 after be found useful in operations of a like nature, the following descrip- 

 tion of its arrangement may not be superfluous : — The apparatus may 

 easily be adapted to the process of fractional distillation in vacuo ; by a 

 slight modification it is possible to change the receiver without disturbing 

 the partial vacuum in the remaining parts of the apparatus. 



A represents the flask from which the liquid is distilled ; it is fitted 

 with a good cork pierced with two holes, into one of which fits a thermo- 

 meter, and into the other a piece of thermometer tubing (B), one end of 

 which nearly reaches to the bottom of the flask, and is drawn out into a 

 fine capillary tube ; to the other end a screw-clamp is fixed by means of a 

 short piece of caoutchouc tubing. The object of this capillary tube is to 



