4 BULLETIN 454, U. S. DEPARTMENT OF AGRICULTURE. 
Table II. — Yield of peppermint oil from the fresh and from the dry herb at various dates 
of distillation and stages of growth during five successive years. 
[All yields of oil calculated on the basis of fresh herb.] 
Description 
1908 
1909 
1910 1911 
1912 
Iyer- 
of material. 
Date. 
Yield. 
Date. 
Yield. 
Date. 
Yield. Date. 
Yield. 
Date. 
Yield. 
age. 
Fresh herb: 
Budding 
Flowering.. 
Fruiting 
Dry herb: 
Budding. . . 
Julv 22 
Aug. 21 
Sept. 25 
P.ct. 
0.23 
.20 
.10 
July 14 
July 24 
Aug. 10 
July 19 
July 26 
Aug. 19 
P.ct. 
0.13 
.12 
.17 
.080 
.042 
.052 
July 28 
Aug. 16 
Sept. 16 
Aug. 5 
Sept. 8 
Sept. 27 
P.ct. 
0.10 
.13 
.10 
.070 
.022 
.04S 
July 17 
Aug. 17 
Sept. 18 
Aug. 15 
Sept. 11 
Oct. 2 
P.ct. 
0.12 
.09 
.13 
.050 
.088 
.040 
Aug. 5 
Sept. 21 
Oct. 5 
P.ct. 
0.09 
.12 
.07 
P.ct. 
0.134 
. 132 
.114 
. 0M 
Flowering . . 
. 050 
Fruiting 
! 
.046 
The average percentage of moisture in the budding, flowering, and 
fruiting plants during the years 1909, 1910, and 1911 was 78.2, 74.2, 
and 69 per cent, respectively. The yield of oils obtained from the 
dried plants is lower in every case than from the fresh material. 
The general average yield is approximately 50 per cent lower than 
the yield obtained from the fresh herb at the same stage of growth. 
It appears, therefore, that prolonged drying of the herb before dis- 
tillation is decidedly detrimental to the yield of oil obtainable. 
In an experiment to determine what effect drying the plant has on 
the yield and constants of the oil, Todd 2 states that no loss of oil 
results when the plant is dried before distillation and that the color 
and solubility of the oil from the dried plants are superior to those 
from the fresh plants. The specific gravity, however, is slightly higher. 
From the general averages during the three successive stages of 
growth of the plants, it appears that the yield of oil tends to decrease 
as the plant matures. 
Information regarding the distribution of the oil in the plant was 
obtained by distilhng separately the leaves and the tops of the plants 
at the three successive stages of growth and comparing these results 
with those recorded for the whole fresh herb. The results of these 
experiments are shown in Table III. 
Table III. — Comparison of yields of peppermint oil from the fresh leaves, from the tops, 
and from the whole fresh herb at different stages of growth during three successive years. 
Parts of plant and stage of growth. 
Yield of oil (per cent). 
1909 
1911 Average. 
Whole herb: 
Budding.. 
Flowering. 
Fruiting... 
Leayes: 
Budding.. 
Flowering. 
Fruiting... 
Tops: 
Budding.. 
Flowering. 
Fruiting... 
0.13 
.12 
.17 
.20 
.27 
.13 
.20 
.16 
.19 
0.10 
.13 
.10 
.15 
.25 
.10 
.12 
0.12 
.09 
.13 
.26 
.39 
.15 
.22 
.42 
.19 
0.116 
.113 
.133 
.203 
.303 
.120 
.173 
.233 
.153 
i Todd, A. M. An experiment with peppermint plants. In Amer. Drug., y. 15, no. 9, p. 161. 
1886. 
