10 
BULLETIN 454, U. S. DEPARTMENT OF AGRICULTURE. 
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 
80 per 
cent 
alcohol. 
Free 
acid 
(as 
acetic). 
Ester 
(mon- 
th yl 
ace- 
tate). 
Menthol. 
I 
Free. Total. 
1 
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. 
a0. 9231 
a . 9242 
a. 9250 
o 
-9.4 
-6.5 
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 1\ 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 less in the 
stems, which accounts for the lower ester content of the oil distilled 
from the whole plant. 
