ATTAR  OF  ROSE. 
13T 
make  some  preliminary  trials  as  to  the  congealing  point.  Thus  it 
will  be  seen  that  the  business  of  adulterating  attar  is  somewhat 
troublesome,  but  honest  dealing  out  of  the  question,  it  is  very 
profitable. 
Many  attempts  have  been  made  to  discover  some  chemical  re- 
action which  would  reveal  the  falsification  of  attar  with  geranium 
oil,  but  hitherto  mostly  in  vain.  As  completely  deceptive  may 
be  noticed  Guibourt's  test  with  the  vapor  of  iodine  ;  and  also 
that  with  K  I  and  starch.  The  author  has  had  the  opportunity 
of  preparing  a  standard  attar  of  rose  on  the  spot  and  was  also 
in  a  position,  such  as  scarcely  another  chemist  ever  was,  for  in- 
vestigating the  whole  subject.  Pure  attar  gives  with  iodine  and 
with  iodide  of  potassium  and  starch  the  same  reactions  as  when 
it  is  mixed  with  geranium  oil,  and  even  those  with  pure  geranium 
oil  are  hardly  different.  The  proposed  test  of  N05,  N04  and 
S03  are  equally  devoid  of  value. 
Among  reactions  such  as  these  there  is  not  one  of  real  im- 
portance for  the  recognition  and  determination  of  geranium  oil 
when  mixed  with  attar.  The  author  has  learnt  to  distinguish 
but  one  constant  character  for  geranium  oil,  which  is  that  of 
not  diverting  a  ray  of  polarized  light ;  whilst  attar  in  a  tube  of 
100  mm.  rotates  the  ray  4°  to  the  right.  Here  is  the  single 
handle  for  the  examination  of  a  suspected  attar.  Considerable 
difficulties  are  certainly  in  the  way  of  using  such  a  test.  The 
differences  observable  are  very  small,  and  the  test  is  in  fact  ap- 
plicable only  in  the  case  of  very  gross  adulteration.  In  the  use 
of  a  longer  tube  (say  about  200  mm.)  there  are  difficulties  from 
the  color  of  the  oil  and  its  want  of  transparency.  The  author 
.  has  recently  made  trials  of  another  form  of  polarizing  apparatus 
constructed  expressly  for  the  purpose,  which  has  enabled  him  to 
detect  in  attar  of  rose  so  small  an  addition  of  geranium  oil  as  5 
per  cent. ;  but  such  an  apparatus  is  somewhat  expensive,  and 
much  practice  is  required  in  order  to  use  it  effectively.* 
*  The  difficulties  of  employing  polarized  light  for  the  discrimination  of 
attar  are,  in  my  opinion,  too  considerable  for  the  test  to  be  at  present  of 
any  practical  value.  I  may  refer  to  some  experiments  on  the  subject 
made  in  1857  by  my  friend  Dr.  De  Yry,  the  results  of  which  by  no  means 
accord  with  those  obtained  by  Dr.  Baur. — D.  H. 
