10 



BULLETIN 454, U. S. DEPABTMENT OF AGBICULTTTBE- 



Table V. — Comparison of the physical properties and the chemical composition of pepper- 

 mint oils distilled from the fresh leaves, from the tops, and from the entire fresh herb at 

 the various stages of growth — Continued. 





Physical properties. 



Chemical composition (per 

 cent). 



Year and descrip- 

 tion of material. 



Color, odor, and taste. 



Specific 

 gravity. 



Rota- 

 tion, 

 50 mm. 

 tube. 



Refrac- 

 tion. 



Solubil- 

 ity in 

 SO per 

 cent 



alcohol. 



Free 

 acid 



(as 

 acetic). 



Ester 

 (men- 

 thyl 

 ace- 

 tate). 



Menthol. 





Free. 



Total. 



1910. 



Flowering stage — 

 Continued. 

 Leaves 



Tops 



Pale yellow; strong 

 minty odor; 

 slightly fatty, 

 bitter, pungent, 

 cooling taste. 



Pale yellow; frag- 

 rant, agreeable 

 odor; fatty, bitter, 

 pungent, cooling 

 taste. 



Yellowish green; 

 very fragrant flow- 

 ery odor; very 

 bitter, s 1 i g h tly 

 pungent taste. 



Golden yellow; 

 strong minty 

 odor; bitter, cool- 

 ing, slightly pun- 

 gent taste. 



Greenish yellow; 

 agreeable, flowery 

 odor; bitter, 

 slightly pungent, 

 cooling taste. 



aQ. 9231 

 a . 9212 



a . 9250 



-9.4 

 -6.5 



-7 



61.4753 

 61.4780 



61.4712 

 61. 4720 

 61. 4738 



Volumes. 

 c0. 7 



c.8 

 d.8 



1.90 

 1.43 



1.14 



4.80 

 3.30 



22.27 

 22.98 



20.86 

 43.40 

 28.29 



37.83 

 48.60 



12.7 



55.38 

 66.71 



Fruiting stage: 

 Herb 



29.14 







Tops 

























a At 24° C. 

 6 At 22° C. 



c Turbid in 11 volumes or more. 

 d Turbid in 2" volumes or more. 



During all the stages of growth the content of free acetic acid is 

 consistently higher in the oils from the leaves and tops than in the 

 oils from the whole herb. High acidity is usually accompanied by a 

 correspondingly high percentage of menthyl acetate. This is clearly 

 demonstrated by the oils from the leaves and tops at the flower- 

 ing and fruiting stages in 1910, when the percentage of acid varied 

 from 1.14 to 4.8 and the menthyl acetate from 20.86 to 43.4 per 

 cent. 



The ester content of the oils from both leaves and tops increases 

 as the plant matures, the fruiting stage producing the oils richest in 

 this constituent. The percentage of esters in the oils from the leaves 

 and tops is higher in nearly every instance than in the oil from the 

 whole fresh herb. It is very probable, therefore, that the esterifica- 

 tion of the acetic acid and menthol takes place most readily in these 

 parts of the plant. The formation of esters is no doubt loss in the 

 stems, which accounts for the lower ester content of the oil distilled 

 from the whole plant. 



