38 Report of Schimmel § Co. April/October 1917. 



Rabak further tried to form an estimate in what manner shading had any effect 

 on the production of peppermint oil and on its qualities. For this purpose he not 

 only planted peppermint on a bed on which the intensity of light was reduced about 

 50 percent, but also on one of the same size which remained unshaded 1 ). 



The oil yield was about the same; on the whole the oils from both beds showed 

 little difference. Oil from plants grown in the shade contained rather less acid, 

 menthyl acetate, free menthol, and total menthol than oil from plants reared in full 

 daylight. Accordingly it appears that the formation of esters as well as of menthol 

 is retarded by shading. The properties of the oils were the following: — 



Oil from herb grown in full daylight: d 2S o 0.9233 and 0.9273; « D — 11.4° and 



— 14.6°; n D23 o 1.4722 and n D22 o 1.4820; acid content (calculated as acetic acid) 0.03 and 

 0.20 percent.; ester content (calculated as menthyl acetate) 11.67 and 13.79 percent; 

 free menthol 30.94 and 34.11 percent; total menthol 40.13 and 44.97 per cent. 



Oil produced from shade-grown plants: d 23 o 0.9192 and 0.9343; « D — 4.48 and 



— 6.8°; n D23 o 1.4708 and n D22 o 1.4724; acid content (calculated as above) and 

 0.07 per cent; menthyl acetate 10.96 and 13.08 per cent; free menthol 24.43 and 

 31.20 percent; total menthol 33.07 and 41.50 percent. 



Finally, Rabak also mentions the effect of frost on the quality of the peppermint 

 oil. Oil from frozen plants smells pleasanter and more flowery, probably owing to the 

 high menthol and ester content; hence it is also comparatively easily soluble and may 

 perhaps contain less terpenes 2 ). 



The oil produced from frozen plants showed the following properties: — d 2 4o 0.9107 

 and d 23 o 0.9155; « D — 33 and — 23°; n D230 1.4580 and n D25 o 1.4592; acid content (calculated 

 as above) 0.09 per cent.; menthyl acetate 40.66 and 24.3 per cent.; free menthol 28.93 

 and 40.7 per cent; total menthol 60.97 and 67.8 per cent. 



Rabak's statements concerning the oil yields from dry and fresh plants are partly 

 at variance with the observations of other scientists and with the results of practical 

 experience 3 ). We will not omit to mention, however, that comparative experiments 

 on the decline of the yield in volatile oil during the process of drying plants are 

 exceedingly difficult, especially in the case of such containing much water. Losses 

 up to 50 per cent of oil during drying, as Rabak mentions, may well be caused by 

 inappropriate treatment of the herb during the drying process. Before the fact was 

 known that fresh material for distillation easily retains part of the oil, scientists even 

 imagined that the oil content increased during drying, till exhaustive distillation tests 

 proved that this idea was altogether erroneous. Fresh distillation material produces, 

 when completely distilled, a yield in oil differing little or not at all from that produced 

 by the same initial substance when distilled in a highly faded state, calculated on fresh 

 plants, on the condition that the drying process is performed in an appropriate manner. 

 The realisation of the fact that fresh plants can only be distilled completely with much 

 loss of time and steam, owing to repeated interruption of the distillation process, in 

 order to enable the contents of the still to get dry, has lead to the result that in 

 practice*) peppermint plants are almost invariably distilled in a highly faded or dry 

 state, whereby the highest yield in oil is obtained with the least expense. 



x ) H. J. Henderson obtained, on'ilVe contrary, from plants on sunny sites 0.409 per cent, of oil and from 

 plants on damp, shady spots only 0.1 per cent, of oil. (Gildemeister und Hoffmann, Die atherischen Ole, 

 2 nd ed., vol. Ill, p. 578.) — 2 ) A similar effect has also been obseryed in the case of bergamot mint oil (Mentha 

 citrata, Ehrh.), the product obtained from frozen herb containing much more Iinalyl acetate than otherwise. 

 (Gildemeister und Hoffmann, Die atherischen Ole, 2 nd ed., vol. Ill, p. 590.) — 3 ) v. Rechenberg, Theorie der Ge- 

 winnung und Trennung der atherischen Ole durch Destination, p. 278 and 279. — 4 ) Comp. preceding note, p. 461. 



