8 



TEMPERA TURE 



FIG. 2. Percentage weight-steam temperature curve for 

 a mixture of two oils distilled through a dephlegmator. 



be obtained, which shows graphically what has happened during dis- 

 tillation. This curve shows that with the increase in the total per- 

 centage of oil distilled, the 

 boiling temperature grad- 

 ually rose, indicating that 

 the proportion of the 

 higher boiling oil increased 

 in the later fractions. It 

 also shows that the two 

 oils are mixed in the vari- 

 ous fractions in varying 

 proportions. 



If, however, the same 

 mixture is distilled through 

 a dephlegmator, the per- 

 centage weight-boiling 

 temperature curve will 

 take a form similar to that 

 shown in figure 2. In this 

 figure the curve shows that 

 during the first part of the distillation from a to Z> the temperature 

 remained nearly constant, from b to c the temperature rose rapidly, 

 while from c to d the temperature was again practically constant 

 and remained so until the end of the process. It is evident, there- 

 fore, that a curve which is 

 nearly vertical indicates 

 that the distillate during 

 that portion of the distilla- 

 tion consists of a nearly pure 

 substance, while a curve 

 which rises slowly toward 

 the right or is nearly hori- 

 zontal indicates that the 

 distillate is composed of two 

 or more substances. A com- 

 parison of figure 1 with fig- 

 ure 2 shows clearly the more 

 complete fractionation due 

 to dephlegmation, and also 

 shows that when dephleg- 

 mation is used the shape of 

 the curve gives a more accu- 

 rate picture of the composi- 

 tion of the mixture distilled. 



Figure 3 is the type of curve obtained when the oil distilled consists 

 chiefly of one substance with a relatively small admixture of higher 

 boiling substances. 



[Cir. 152] 



TEMPERA 

 FIG. 3. Percentage weight-steam temperature curve for 

 a nearly pure oil mixed with small quantities of higher 

 boiling substances distilled through a dephlegmator. 



