644 Mr. A. F. Dtifton on the Separation 



In the experiments described above, the column was lagged 

 with cotton-wool to reduce the loss of heat, so that the liquid 

 condensed was not sufficient to " flood " the column and to 

 obstruct the upward flow of vapour. Experiments were 

 made to determine the effect of further reduction in the 

 amount of heat lost. The amount of lagging was increased 

 until the maximum rate of heating to yield pure benzene 

 was 151 calories per minute. In an experiment with a heat 

 supply of 158 calories per minute the distillate contained a 

 trace of toluene. For 151 calories per minute the thermal 

 efficiency was 38 per cent. With a heat supply of 143 

 calories per minute it was 25 per cent. These experiments 

 show that the thermal efficiency is reduced if loss of heat in 

 the column be unduly prevented. 



A. shorter column, 25 cm. in length, was constructed with 

 a bore of 0*3 cm. at the top and 0*7 cm. at the bottom, the 

 wire for the spiral being the same throughout. With this 

 column it was necessary to reduce the rate of heating as the 

 proportion of benzene in the mixture diminished. Table VI. 

 shows the results obtained in an experiment with this column. 

 The thermal efficiency for a mixture containing 75 per cent. 

 of benzene was over 70 per cent., and for mixtures con- 

 taining more than 50 per cent, of benzene the column was 

 more efficient than the 105 cm. column. 









Table VI. 









Time 



minutes. 



c.c. 

 collected. 



c.c. 

 per 

 min. 



Mixture 



per cent, of 



benzene. 



Temp. 



°C. 



Calories 



per 



min. 



Thermal 

 efficiency 

 per cent. 







00 





80 





1055 





10 



4-6 



0-54 



78 



79-7 



105'5 



78 



20 



9-9 



0-44 



75 



80-2 



935 



72 



30 



13-7 



0-375 



72 



80-2 



88-5 



66 



40 



17-25 



0335 



70 



801 



84-5 



62 



50 



20-5 



0-32 



66 



80-2 



84-5 



61 



60 



236 



9-29 



62 



80-25 



84-5 



57 



70 



26-25 



0-235 



58 



80-2 



77-5 



52 



80 



28-4 



0-195 



54 



80-2 



75 



47 



90 



30-2 



0185 



50 



80-2 



73 



46 



100 



31-8 



0-145 



45 



80-2 



69 



41 



no 



33-05 



0105 



41 



80-2 



675 



32 



120 



33-9 



0-06 



38 



80-3 



63 



20 



