8 BULLETIN 454, U. S. DEPARTMENT OF AGRICULTURE. 
the oil from the fruiting plant in 1908, which contains 53.55 per cent 
of total menthol, and in the oils from the flowering plant in 1909 
and the budding plant in 1910, which contain, respectively, 52.09 
and 56.85 per cent of total menthol. 
In comparing the oils from the dry herb with those from the fresh 
herb it will readily be observed that the content of free acetic acid 
is uniformly higher in the oil from the dry plants. It is interesting 
to note that in practically every instance the ester content is also 
higher than in the oils from the fresh plants. It would appear, 
therefore, that during the drying process there occurs a chemical 
change which is favorable to esterincation. Notwithstanding the 
higher content of esters, the odor of the oils was decidedly inferior. 
This is attributed to the presence of certain volatile substances 
formed during drying, which distilled over with the oils and imparted 
an objectionable herby odor to them. 
The free menthol and the total menthol content of the various oils 
from both the dry and the fresh plants appears to be similarly affected, 
as the percentage of both free and total menthol is uniformly high. 
It is, however, doubtful whether the increased content of ester and 
menthol in the dry plants would warrant the drying of the plants 
before distillation, since, as previously noted, a considerable percent- 
age of oil is lost when the plants are dried. 
The distillation of peppermint oil from plants in a fresh condition at 
different periods of growth up to the time of flowering has been 
reported by Charabot, 1 who finds that the density and rotation 
diminish during vegetation. The plant is richest in menthol at the 
appearance of vegetation and lowest in the combined menthol, or 
esters. As the growth of the plant progresses, the percentage of the 
combined menthol, or esters, increases. 
A study was made of the physical and chemical properties of the 
oils distilled separately from the fresh leaves and flowering tops, and 
for comparison the results are presented with those obtained for the 
oils from the whole fresh herb, as shown in Table V. 
The general characters of the oils from the leaves and tops at the 
successive stages of growth are very similar to those of the oils from 
the entire herb. The specific gravity and rotation of the oils from 
the leaves and the tops are higher in nearly every case than the same 
constants of the oils from the entire herb. The refractive indexes are 
variable, while the solubiiitv in SO per cent alcohol is less in most 
cases than that of the oils from the whole herb. These constant 
differences in specific gravity, rotation, and solubility apparently 
denote a difference in the composition of the oils from the leaves and 
tops as compared with that from the whole herb. 
'- Charabot, Eugene. Rechercb.es sur les migrations et les metamorphoses des composes terpeni- 
ques dans la menthe poivr^e. In Bui. Soc. Chim. Paris, s. 3, t. 23, p. 466-474. 1900. 
