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 esterification. 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 solubility in 80 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. Recherches sur les migrations et les metamorphoses des composes terpeni- 

 ques dans la menthe poivre"e. In Bui. Soc. Chim. Paris, s. 3, t. 23, p. 466-474. 1900. 



