386 
Current  Literature. 
Am.  Jour.  Pharm. 
Aug.,  19 1 7. 
Factors  Affecting  the  Yield  and  Quality  of  Peppermint  Oil. 
The  effect  on  the  yield  and  quality  of  peppermint  oil  of  cultural 
and  climatic  conditions  is  discussed  in  professional  paper  No.  454, 
by  Frank  Rabak,  chemical  biologist,  Bureau  of  Plant  Industry. 
This  bulletin,  recently  published  by  the  U.  S.  Department  of  Agri- 
culture, is  based  on  experiments  in  raising  and  distilling  peppermint 
plants  conducted  from  1908  to  1912.  Conditions  of  soil  and  climate, 
the  author  finds,  are  influential  factors  in  the  formation  of  oil  and  its 
constituents  in  the  peppermint  plant.  Light  sandy  or  loamy  soil  ap- 
peared to  be  most  favorable  for  the  production  of  an  oil  of  high 
quality. 
Distillation  experiments  were  conducted  with  a  view  to  deter- 
mining the  effect  on  oil  yield  of  drying  the  plants  previously  to 
putting  them  in  the  stills.  It  was  found  that  the  yield  of  oil  from 
fresh  plants  apparently  decreases  as  the  plant  matures.  Drying  the 
plants  before  distillation  results  in  a  considerable  loss  of  oil.  The 
largest  proportion  of  oil  is  found  in  the  leaves  and  flowering  tops. 
In  experiments  in  distilling  plants  and  parts  of  plants  at  different 
times  of  growth,  the  author  found  that  the  percentage  of  esters  in  the 
oil,  which  give  the  oil  its  fragrant  minty  odor,  increases  as  the  plants 
approach  maturity.  The  menthol  content  of  the  oil  bears  a  close 
relationship  to  the  ester  content.  The  free  acidity  and  ester  content 
of  the  oil  distilled  from  dry  plants  is  considerably  higher  than  in  the 
oil  from  fresh  plants.  The  drying  of  the  plants  causes  conditions 
favorable  to  making  esters,  while  the  percentage  of  free  and  total 
menthol  in  oil  produced  from  dried  plants  is  also  uniformly  high. 
It  was  found  also  that  the  formation  of  esters  and  menthol  takes 
place  most  readily  in  the  leaves  and  tops  of  the  plants. 
In  another  test  it  was  found  that  the  effect  of  shade  upon  the 
peppermint  plant  is  to  decrease  the  making  of  esters  and  the  for- 
mation of  menthol.  Experiments  with  plants  allowed  to  freeze  indi- 
cate that  frost  noticeably  increases  esterification  and  the  formation 
of  menthol. 
