158  Some  Notes  on  Essential  Oils.  {^m'l%T\\]vm*m' 
MUSTARD. 
Oil  of  mustard,  essential  true   50 
Oil  of  mustard,  synthetic   30 
ROSE. 
Oil  of  rose,  geranium   2  to  10 
Oil  of  rose,  artificial   20  to  40 
Oil  of  rose,  good   .  .   50  to  60 
Oil  of  rose,  best                          .   80  to  100 
WINTERGREEN. 
Oil  of  wintergreen,  true   30 
Oil  of  wintergreen,  sweet  birch   15 
Oil  of  wintergreen,  synthetic   5 
These  comparative  prices,  while  of  themselves  interesting,  open  up 
the  very  grave  as  well  as  important  question  of  substitution  or  adul- 
teration. It  will  readily  be  appreciated  that  a  synthetic  oil  of 
bitter  almonds,  for  instance,  that  is  approximately  one-third  the  price 
of  the  so-called  natural  and  only  one-sixth  the  price  of  the  true,  may 
be  and  often  is  substituted  for  one  or  the  other. 
This  feature  will  be  referred  to  again  under  the  headings  of  the 
different  essential  oils. 
Oil  of  Bitter  Almonds. — Gildemeister  and  Hoffmann  say  that 
but  a  very  small  proportion  of  the  so-called  natural  oil  is  made  from 
bitter  almonds.  It  is  more  frequently  made  from  apricot  and  peach 
kernels.  The  amount  of  hydrocyanic  acid  in  the  natural  oil,  accord- 
ing to  the  same  authorities,  may  vary  from  i-6o  to  11-4  per  cent, 
with  a  corresponding  specific  gravity  of  from  1*052  to  1*096. 
It  would  appear  from  the  above  quoted  authorities  that  natural 
or  true  oil  of  bitter  almonds  varies  very  considerably  in  physical 
properties,  as  well  as  chemical  composition.  It  would  further 
appear  from  current  literature  that  it  is  practically  impossible  to  find 
an  absolutely  pure  natural  oil  on  the  market  at  the  present  time. 
Edward  Kremers,  in  a  review  of  oil  of  bitter  almond  (Fhatm.  Rev., 
1902,  page  127),  gives  some  interesting  data  on  the  subject,  and 
among  other  interesting  points  reports  the  systematic  examination 
of  twenty-six  commercial  specimens  of  oil  of  bitter  almonds.  Twenty- 
one  of  these  twenty-six  commercial  specimens  contained  chlorine, 
only  nine  of  the  specimens  contained  any  trace  of  hydrocyanic  acid, 
only  four  of  the  nine  having  more  than  2  per  cent.  The  specific 
gravity  varied  from  1-0015  to  1-0779,  tne  benzoic  acid  from  0-91  to 
12-02  per  cent. 
