-8J-0 



60-0 



642 Mr. A. F. Dufton on the Separation 



purity of the distillate, a rise of one degree above the boiling- 

 point of benzene corresponding to 2*78 per cent, of toluene. 

 The thermometer was calibrated in position in the apparatus 

 by the distillation of pure benzene, the boiling-point, cor- 

 rected for atmospheric-pressure variation, being taken as 

 £0°-2 C. 



After some preliminary experiments, a series of four was 

 made in which the only variation was in the rate of heating. 

 In the first, with a heat supply of 170 calories per minute, 

 pure benzene was separated, and when 39'5 c.c. out of the 

 40*0 c.c. of benzene had been collected, the thermometer 

 fell and distillation ceased. At 178 calories per minute, in 

 the next experiment, a trace (0*5 per cent.) of toluene passed 

 over during part of the run. Distillation ceased when 

 39 "3 c.c. had been collected. With a heat supply of 

 193 calories per minute there was a little more toluene in 

 the distillate, and at 206 calories per minute still more. 



Fig. 3. 

 Effect of Excessive Heat Supply on Purity of Distillate. 







206 calories/min 







J 193 calories/min 



^/ 



■/ '^^^^ \v/\. '^ CALORIES /MIN 



""^ HO CALORlEs/lMIN "NA 



50 



100 



ilNUTES 



In these two experiments, after 40 c.c. had been distilled 

 the temperature rose suddenly and toluene began to pass 

 over. The temperature-time curves for the four experi- 

 ments are plotted in fig. 3. The experiments show that 

 for a given column there is an upper limit to the rate ol 

 heating, above which the distillate is not pure. 



