326 
ADULTERATION  OF  ESSENTIAL  OILS. 
some  other  oils,  so  that  this  reagent  may  serve  for  the  detection 
of  oils  free  from  oxygen,  especially  oil  of  turpentine,  in  those 
which  contain  oxygen.  Turpentine  cannot  be  detected  by  this 
means  in  oils  which  are  themselves  free  from  oxygen,  such  as 
oil  of  lemons,  oil  of  orange,  or  oil  of  juniper. 
A  fragment  of  nitroprusside  of  copper,  of  the  size  of  a  pin's 
head,  is  brought  in  contact  with  a  small  quantity  of  the  oil  to  be 
tested  in  a  test-tube  ;  it  is  heated  until  the  oil  begins  to  boil,  kept 
boiling  only  for  a  few  seconds,  and  then  allowed  to  settle.  If 
the  oil  be  an  oxygenated  oil  free  from  turpentine,  the  nitroprus- 
side of  copper  becomes  black,  brown  or  gray,  and  the  supernatant 
oil  changes  its  color  and  usually  appears  darker.  If  the  oil  con- 
tains turpentine,  the  deposit  is  of  a  fine  green,  or  bluish-green, 
and  the  supernatant  oil  colorless  or  slightly  yellow. 
The  above-mentioned  conditions  must  be  exactly  observed. 
If  necessary  the  lens  must  be  employed  to  ascertain  the  changes 
of  color,  for  even  the  color  of  nitroprusside  of  copper  treated 
with  oil  of  turpentine  is  different  and  more  intense  than  its 
original  color.  Sometimes  also  it  is  advisable  to  make  experi- 
ments with  pure  oil. 
Of  the  oils  free  from  oxygen  the  author  investigated  the  fol- 
lowing, and  found  their  action  the  same  as  above  described,  even 
when  the  boiling  was  continued  longer  ;  it  was  only  in  !NTo.  7  a 
and  e  that  the  oil  became  darker,  but  the  deposit  was  of  a  more 
intense  green. 
1.  Petroleum,  crude  and  rectified  ;  2.  Oil  of  bitter  oranges ; 
3.  Oil  of  sweet  oranges ;  4.  Oil  of  orange  flowers  ;  5.  Oil  of 
juniper  berries  ;  6.  Oil  of  sa,vin ;  and  7.  Oil  of  turpentine :  a9 
crude  German  ;  h,  crude  French ;  <?,  rectified  French  ;  d,  German 
rectified  over  lime  ;  and  e,  very  old,  rectified  French,  which  had 
become  thick. 
The  oils  containing  oxygen  behave  similarly  in  general,  but 
even  here  small  differences  occur.  Of  the  oils  from  the  Um~ 
helliferce  the  author  tested, — 
1.  Oleum  Carui,  prepared  from  the  seeds  and  from  the  stalks, 
pure  and  mixed  with  oil  of  turpentine.  The  pure  oil,  when 
boiled  with  the  reagent,  rapidly  became  turbid ;  the  precipitate 
was  deposited  with  difficulty ;  the  change  of  color  was  more  dis- 
tinct the  longer  the  boiling,  and  the  older  the  oil.    An  addition 
