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}  The  Rotatory  Power  of  Volatile  Oils.  3 1 1 
sassafras  oil,  the  Safrol  C10H10O2  whose  chemical  constitution  is  still 
unknown,  but  may  bear  some  relation  to  Anethol  C10Hl2O,  and  Eugenoi 
C10H12  02.  Mustard  oil  and  oil  of  bitter  almonds  do  not  rotate  at 
all,  the  other  six  oils  only  in  a  slight  degree  on  account  of  containing 
traces  of  other  volatile  oils,  probably  Carbohydrogens. 
The  addition  of  oils  able  to  turn  the  plane  of  polarization  may  be 
easily  detected  in  oils  which  do  not  affect  polarized  light.  We  must 
declare  mustard  oil  or  oil  of  bitter  almonds  as  impure,  which  shows 
only  the  least  rotating  power,  and  also  oil  of  anise,  staranise,  gaultheria^ 
cloves,  rose,  sassafras,  cinnamon,  which,  in  the  tube  of  Wild's  Polar- 
istrobometer  of  50  millimeters  length,  would  indicate  more  than  a  few 
degrees.  But  the  possibility  of  an  adulteration  is  not  excluded,  although 
the  samples  of  these  oils  may  not  show  any  rotating  power.  If 
there  were  a  cheap  ethereal  oil  which  would  not  affect  the  plane  of 
polarization,  it  would  be  an  excellent  means  in  the  hand  of  aix 
adulterator  for  diluting  the  more  expensive  oils.  Such  an  oil  is  scarcely 
to  be  found  in  nature,  but  may  be  easily  prepared. 
The  American  oil  of  turpentine,  of  Pinus  australis  or  Pinus  Taeda^. 
and  the  oil  of  Abies  excelsa,  turn  to  the  right  ;  the  French  oil  of  tur- 
pentine of  Pinus  maritima  (Pinus  Pinaster)  and  of  other  species,, 
strongly  to  the  left.  By  preparing  a  mixture  of  such  two  oils,  acting 
in  opposite  direction,  it  would  be  comparatively  easy  to  obtain  an  oil 
without  effect  on  polarized  light.  Oil  of  turpentine  is  by  no  means 
the  only  one  possessing  such  properties.  Sainte-Claire  Deville  found 
oil  of  elemi  to  have  a  left  rotation  ;  the  author  observed  a  right  one  in 
oil  of  Manila  elemi.  Carvol  from  caraway  turns  to  the  right,  from 
crisped  mint  to  the  left.  Some  camphors,  gums,  sugars,  organic  acids 
and  alkaloids  are  cited  as  compounds,  either  chemically  identical  or 
closelv  related,  and  still  of  very  different  optical  behavior. 
Mixtures  in  which  the  rotatory  power  of  one  substance  is  neutralized 
by  the  opposite  action  of  another  accompanying  body,  are  to  be  ex- 
pected in  nature,  and  in  fact,  present.  Very  probably  changes  are 
naturally  produced  by  various  unknown  causes. 
In  turpentines  we  find  very  often  constituents  of  opposite  rotating 
power.  Venice  turpentine,  for  instance,  if  diluted  with  aceton  or 
benzin,  turns  to  the  right  ;  the  oil  distilled  from  it  to  the  left,  and 
the  remaining  resin  to  the  right.  Canada  balsam  and  Strassburg  tur- 
pentine have  a  similar  behavior.    It  is  therefore  to  be  assumed  that 
