14 



WOOD TURPENTINES. 



the original and corrected data will not be given, but only the curves 

 obtained by plotting the corrected data ; the curves are sufficient to 

 give the complete interpretation of the results, and there are so many 

 distillations recorded that it would be prohibitive to use the space 

 required by the tabulated data. 



INTERPRETATION OF DISTILLATION CURVES. 



To interpret these curves properly it is necessary to understand the 

 behavior of a mixture of liquids on distillation, and a brief dis- 

 cussion of fractionation by distillation and of distillation curves will 



therefore be given, to be followed 

 by a discussion of the curves ob- 

 tained by the distillation of two 

 different turpentines. 



170 180 190 



BOILING POINT 



THEORETICAL BOILING-POINT CURVES. 



Let us assume a mixture of equal 

 quantities of two volatile liquids, A 

 and B, with boiling points 160 C. 

 and 200 C., respectively. If on 

 distilling this mixture a complete 

 separation of the two components 

 was obtained, then the distillation 

 curves formed by plotting the per- 

 centage of distillate against the 

 boiling point would be represented 

 by the vertical lines AX and BY 

 (fig. 3) ; that is, all of substance A 

 in pure condition would distill over 

 first and then the pure substance B. 



FKACTIONATION BY ORDINARY DISTILLATION. 



Such a complete separation is, 



FIG. 3. Curves illustrating theory * 



of fractional distillation. however, never obtained, because the 



boiling point of one liquid is al- 

 ways affected by the presence of another volatile liquid. In this 

 case some of the higher boiling substance B would distill over with 

 A long before the temperature of the distillation reaches 200, the 

 boiling point of B, and some of the lower boiling substance A would 

 be left in the flask even after the temperature had risen above 160 C. 

 When such a mixture is distilled from an ordinary distilling flask, 

 the distillation curve would therefore be more like curve I in figure 3. 

 This curve shows that the composition of the distillate gradually 

 changes throughout the distillation from pure A to pure B, the first 



