Van Name and Maryott — Chlorination of Benzene. 163 



of about 500 cc capacity and 7 cm internal diameter, fitted with a 

 rubber stopper carrying the electrodes, thermometer, stirrer, 

 inlet and outlet tubes for the chlorine, and a coiled glass 

 tube for water circulation. The bottle was supported in a 

 thermostat stirred by a motor and kept at the desired temper- 

 ature, 10°, by means of an automatically regulated flow of cold 

 water. Water from the thermostat was kept circulating 

 through the glass coil above mentioned by a rotary-pump, 

 which helped greatly in maintaining a constant temperature 

 within the cell. The glass stirrer, of the shape obtained by 

 twisting a flat strip into a spiral, was driven by a separate 

 motor. To prevent escape of chlorine from the cell at the 

 point of entrance of the stirrer stem, the latter turned in a trap, 

 made on the principle of the well-known mercury seal, but 

 filled with glacial acetic acid. The electrodes were round rods 

 of Acheson graphite, the anode having a wetted surface of 

 about 4:0 cm2 at the beginning of an experiment, decreasing with 

 the volume of liquid to about 20 cm2 at the end. 



Chlorine was drawn from a pressure cylinder of the liquid 

 element and washed by passing through acetic acid. Before 

 entering the reaction mixture the gas also passed through 

 a Drechsel bottle supported in the thermostat and containing 

 solution of the same composition as the reaction mixture, thus 

 minimizing the chances of distillation to or from the cell with 

 the gas current. 



In beginning an experiment a weighed amount of benzene 

 was diluted to a known volume by means of a solution of 

 lithium chloride and glacial acetic acid, previously saturated 

 with chlorine. A measured volume of this liquid was placed 

 in the cell, the stirrer and gas current started, and the reaction 

 allowed to proceed until the free passage of chlorine showed 

 that saturation was complete. Samples for analysis were then 

 withdrawn from the cell by means of an exhausted bottle into 

 a 10 cc pipette with stopcock, from which they were run into 

 aqueous sulphurous acid and analyzed as described on 

 page 156. This process was repeated every two hours. 

 Two samples were always taken for duplicate analyses for total 

 chlorine, and extra samples when addition chlorine was also 

 to be determined. The ratio of addition to substitution chlorine 

 seemed at first to be nearly constant, as observed in a similar 

 instance by Slator,* but our later work proved that in this case 

 the constancy is not complete. 



From this ratio and the other results of analysis the loss in 

 concentration of the benzene during each time interval was 

 calculated on the assumption that its products are exclusively 

 monochlorbenzene and benzene hexachloride.f As already 



* Zeitschr. f . physikal. Chemie, xlv, 524, 1903. 



f This assumption is supported by the work of Slator, loc. cit. 



