AmNo0v''i877arm' }    New  Method  of  Detecting  Alcohol.  555 
on  the  small  hole,  and  the  contents  of  the  tube  is  then  strongly  agi- 
tated for  a  few  moments  ;  after  which  the  pointed  end  is  turned  up- 
wards and  the  finger  removed,  to  allow  the  air  condensed  by  the  clos- 
ing of  the  larger  end  to  escape  so  as  to  avoid  unnecessary  loss  of  the 
mixture  ;  and  finally  the  tube  being  again  reversed,  it  is  supported  on 
a  stand  with  its  pointed  end  downwards,  but  not  resting  on  it.  In  this 
upright  position  it  is  left  till  the  oil  has  separated  from  the  water  and 
risen  to  its  surface,  which  in  most  cases  takes  place  in  a  comparatively 
short  time,  leaving  the  aqueous  portion  below  quite  clear  or  very  nearly 
so.  When  such  is  the  case  a  drop  or  two  of  this  portion  is  allowed 
to  escape,  which  is  easily  effected,  either  by  pressure  on  the  cork  or 
stopper,  by  holding  the  upper  part  of  the  tube  in  the  hand  so  that  its 
warmth  may  expand  the  contained  air,  or  by  slightly  drawing  out  the 
cork  (which  will  cause  some  air  to  enter  at  the  pointed  end)  and  then 
pressing  it  in  again  ;  by  one  or  other  of  those  simple  means,  the  neces- 
sary quantity  of  the  aqueous  portion  will  be  easily  forced  out  of  the 
tube.  This  on  being  brought  into  contact  with  three  or  four  drops  of 
the  molybdic  solution  placed  in  a  little  porcelain  capsule  or  on  any 
white  porcelain  or  delf  surface,  will,  if  the  oil  has  been  adulterated 
with  alcohol,  develop  after  a  few  moments  the  characteristic  intense 
blue  reaction  of  that  substance. 
The  molybdic  solution  I  have  employed  for  this  purpose  was  the 
same  as  that  which  I  have  already  recommended  to  be  used  in  the 
adoption  of  my  test  for  the  detection  of  alcohol  generally,  which  is 
readily  prepared  by  dissolving,  with  the  aid  of  a  gentle  heat,  one  part 
of  molybdic  acid  in  ten  parts  by  weight  of  pure  and  concentrated  sul- 
phuric acid.  This  solution  should  be  kept  in  a  well-stoppered  glass 
bottle,  as  it  quickly  absorbs  moisture,  becoming  too  dilute,  and  is 
otherwise  injured  if  it  is  left  exposed  to  the  air. 
As  regards  the  little  testing  tube  I  have  suggested  for  the  examina- 
tion of  the  essential  oils,  I  may  observe  that  if  it  is  properly  constructed 
and  corked  perfectly  air  tight,  it  will  hold  its  contents  without  allowing 
it  to  drop  out  when  not  required  ;  and  if  the  pointed  end  of  the  tube  is 
not  left  touching  any  object,  which  would  withdraw  the  fluid  by  capillary 
attraction,  there  will  only  be  a  veay  trifling  loss  of  the  watery  portion 
from  evaporation  through  the  small  aperture,  even  after  keeping  for  a 
considerable  time. 
