14 



BULLETIN 454, U. S. DEPARTMENT OF AGRICULTURE. 



the oil from the unfrozen plants, possibly because of the greater 

 proportion of menthol in the first-mentioned oil. 



The physical constants reveal marked differences in the rotation 

 and some differences in the solubility in 80 per cent alcohol. The 

 higher rotation of the oil from the frozen plants is attributable to 

 the presence of a greater quantity of the strongly levogyrate com- 

 pounds, menthol and menthyl acetate. 



Table VII. — Comparison of the yields, the physical properties, and the chemical compo- 

 sition of peppermint oils distilled from frozen and from unfrozen plants. 



Items of comparison. 



Frozen plants. 



Unfrozen plants. 



Frozen plants. 



Unfrozen plants. 



Physical properties: 

 Yield, .per cent. 

 Color 



Odor 



Taste 



Specific gravity. 



Rotation, in 50 

 mm. tube, de- 

 grees. 



Refraction 



Solubility in 80 

 per cent alco- 

 hol, volume. 

 Chemical composi- 

 tion (per cent):. 



Free acid (calcu- 

 lated as acetic 

 acid). 



Menthyl acetate. 



Free menthol . . 



Total menthol.. 



0.065 



Pale straw 



Mild, flowery, char- 

 acteristic minty. 



Bitter, pungent, 

 and exceedingly 

 cooling. 



0.9107, at 24° C 



-11.3 



1. 4592, at 25° C 



0.4; clear in excess. 



0.09 



24.3 



40. 7 



67.8 



0.07 



Pale yellowish 



green. 

 Strongly minty 



Pungent, slightly 

 bitter, cooling. 



0.9142, at 24° C.... 

 -8.43 



1.4689, at 22° C 



0.6; turbid in 1* 

 volumes or more. 



0.086. 



8.8 

 31.8 

 38.7 



0.11 



Dark golden yellow 



Flowery, not 

 strongly'minty. 



Bitter, " pungent, 

 and cooling. 



0.9155, at 23° C... 

 -16.5 



1.4580, at 23° C... 



0.6; faintly turbid 

 in 3| volumes or 

 more. 



40.66. 

 28.93. 

 60.97. 



vel- 



0. 077. 



Pale golden 



low. 

 Strongly minty. 



Bitter, slightly 

 pungent, cooling. 



0. 9180, at 23' 

 —11. 7. 



C. 



1.4621, at 23° C 

 0.5; turbid in 2h 

 volumes or more. 



0.12. 



31. 82. 

 9.99. 



35.06. 



The oils from the frozen plants, being readily soluble, remain more 

 or less clear when an excess of 80 per cent alcohol is added, whereas 

 the oils from the unfrozen plants become turbid in one and one-half 

 volumes or more of alcohol. In the oils from the frozen plants, 

 therefore, a higher content of the easily soluble menthol and menthyl 

 acetate, and possibly a lower content of the more or less insoluble 

 terpenes, may be expected. 



In discussing the chemical constants of the oils it is noted that the 

 quantity of free acids is nearly the same for all the oils. The ester 

 content of the oils from the frozen plants, when calculated as menthyl 

 acetate, was 34.3 in 1910 and 40.66 per cent in 1911, which is much 

 higher than the ester content of the oils from the unfrozen plants. 

 During both seasons the percentage of free menthol in the oils from 

 the frozen plants exceeded that in the oils from the unfrozen plants. 

 The total menthol content was also much higher in the oils from the 

 frozen plants than in that from the unfrozen plants. 



If, as in the ordinary esterification reactions, the formation of 

 esters in the plant takes place by the action of the organic acids upon 



