'^""jin^'is^so^""" }  Polarimeter  and  its  Use,  5 1 
mixture  of  peach  kernels  and  almonds,  and  the  artificial,  or  oil  of  mirbane,  are  all 
optically  inactive,  hence  the  polarimeter  does  not  furnish  us  with  a  means  of  dis- 
tinguishing between  them.  Other  results  were  very  satisfactory.  Thus,  finest 
imported  otto  of  rose  is  levogyrate,  giving  a  rotation  of  -  3*52°.  A  common  quality 
was  found  to  be  dextrogyrate  giving  -j-  1*50°.  Now  the  lower  qualities  of  otto  are 
known  to  contain  varying  proportions  of  oil  of  geranium  ;  but  on  examining  the 
only  sample  of  this  oil  which  was  then  at  my  disposal  and  which  had  been  received 
from  the  south  of  France,  it  was  found  to  give  -  6-73°.  This,  then,  could  not  have 
been  the  article  used  in  adulterating  the  sample  in  question  ;  but  subsequently  on 
examining  the  Turkey  oil  of  geranium  a  solution  of  the  problem  was  furnished, 
since  it  gave  a  rotation  of  -\-  1-72°  and  indicated  that  it  constituted  the 
bulk  of  the  so-called  common  otto  of  rose.  It  was  found  too  that  otto  of 
rose  distilled  in  this  country  possessed  an  opposite  rotatory  power  to  rhat  of  the 
finest  imported,  as  indicated  in  the  table  appended  to  this  paper.  On  examining 
many  samples  of  oil  of  lavender  it  was  found  that  some  of  the  commoner  were 
adulterated  with  turpentine,  and  there  was  no  difficulty  in  determining  whether  this 
had  been  done  in  France  or  England,  on  account  of  the  different  rotatory  powers  of 
the  turpentines  in  the  two  countries.  Whilst  prosecuting  this  study  my  attention 
was  directed  to  an  excellent  paper  by  Dr.  J.  H.  Gladstone  on  essential  oils  ("Jour. 
Chem.  Soc,"  new  series,  vol.  ii,  p.  i),  in  which  he  gives  the  specific  gravity,  rotatory 
power  and  refractive  indices  of  a  number  of  essential  oils  ;  also  to  a  less  important 
paper  by  Dr.  Julius  Maier,  of  New  York,  **  Detection  of  the  Adulteration  of 
Essential  Oils  with  Oil  of  Turpentine"  ("Chem.  News,"  vol.  xi,  p.  301,  from  the 
**Amer.  Jour.  Sci.,"  xxxix,  p. 273).  Since  the  publication  of  these,  some  oils  have  come 
into  use  which  were  then  less  known  than  at  the  present  time,  and  some  others  are 
now  supplied  from  different  localities  j  it  was  therefore  thought  desirable  to  go  over 
the  ground  anew  and  compile  a  table  giving  the  rotatory  power  and  specific  gravity 
of  a  somewhat  larger  number.  Such  a  table  is  appended  to  this  paper,  the  samples 
of  oil  operated  on  being  the  most  reliable  I  could  obtain,  except  where  a  second 
quality  is  mentioned  for  comparison,  and  all  that  were  sufficiently  colorless  to  be 
viewed  through  a  column  of  200  mm.  were  so  examined.  Some  oils,  such  as  those 
of  hops,  cassia,  chamomiles,  myrtle,  etc.,  could  only  be  read  through  100  mm. ; 
whilst  some  such  as  patchouli  and  cajuput,  admitted  only  sufficient  light  through  50 
mm.  All  have  been  calculated  to  100  mm.  and  at  a  temperature  of  i5-5°C.  Many 
results  were  obtained  which  being  unimportant  are  not  here  recorded,  but  all  tended 
to  experience,  and  as  deductions  from  which  might  be  mentioned  that  turbidity  even 
though  very  slight,  materially  interferes  with  the  accuracy  and  sharpness  of  the 
readings  5  it  is  therefore  necessary  to  filter  any  oils  or  solutions  which  are  not  per- 
fectly bright.  Age  does  not  influence  to  any  extent  the  optical  activity  of  essential 
oils.  Oil  of  cloves,  new  and  colorless,  and  samples  of  a  light  sherry  and  dark  sherry 
color  all  registered  very  nearly  the  same,  and  samples  of  English  oil  of  lavender 
less  than  a  year,  four  years  and  five  years  old  differed  from  each  other  less  than  one 
degree. 
The  modus  operandi  is  exceedingly  simple.  A  correct  zero  must  be  first  obtained 
thus — one  of  the  tubes  being  filled  with  distilled  water,  the  glass  disc  is  slid  on  so 
