312  Em  to  Detect  Adulteration  of  Oils.    { AKj^;  1P8?2ARM- 
from  ten  to  twenty  drops  of  a  known  sample  of  pure  linseed  oil.  at  the 
other  an  equal  quantity  of  that  suspected ;  to  each  add  one  drop  of 
oil  of  vitriol.  On  the  pure  linseed  oil  a  dark-brown  spot  slowly  forms  ; 
if  the  suspected  sample  contains  rosin  oil,  a  dark  reddish-brown  spot 
quickly  forms,  retaining  its  red  color  for  a  long  time,  and  a  peculiar 
scum  forms  over  it.  Rosin  oil  may  be  detected  in  boiled  linseed  oil 
in  a  similar  manner,  and  with  the  same  certainty,  the  reactions  being 
more  rapid.  A  sample  of  genuine  boiled  oil  must  be  used  for  the 
comparison.  The  rosin  oil  used  in  adulterating  linseed  oil  is  half  the 
price  of  the  latter  ;  it  is  free  from  smell  even  when  heated  ;  it  has  a 
peculiar  metallic  taste,  which  is  not  masked  by  the  linseed  oil.  It 
greatly  retards  the  drying  properties  of  linseed  oil,  causes  it  to  re- 
main 4  tacky '  for  some  time,  and  prevents  it  ever  becoming  hard.'' 
To  detect  the  Purified  Mineral  Oil  used  in  the  Adulteration  of  re- 
fined Rape  [Colza)  Oil. — The  mineral  oil  is  rather  lighter  than  rape 
oil,  having  a  specific  gravity  of  0*902  (the  gravity  of  refined  rape 
being  about  0*914).  When  mixed  with  rape  it  may  be  detected  by  a 
slight  but  peculiar  smell  on  gently  heating,  and  by  a  slightly  dis- 
agreeable taste.  It  imparts  the  opalescent  appearance  peculiar  to 
all  earth  and  mineral  oils.  Bright  wavy  streaks  may  also  be  seen 
when  an  adulterated  sample  is  mixed  with  a  pure  sample,  as  described 
above,  but  in  this  instance  the  pure  oil  should  be  added  first.  Place 
a  slab  of  clean  glass  on  a  piece  of  white  paper,  at  one  end  put  from 
ten  to  twenty  drops  of  a  known  sample  of  refined  rape,  at  the  other 
an  equal  quantity  of  that  suspected  ;  to  each  add  one  drop  of  oil  of 
vitriol.  On  the  pure  rape  a  pale  yellow  spot  slowly  forms,  throwing 
out  dirty  orange  streaks ;  on  the  adulterated  sample  a  reddish-brown 
spot  quickly  forms.  Mineral  oil  interferes  greatly  with  the  burning 
of  refined  rape,  causing  smoke  and  great  deposit  on  the  wick. 
Detection  of  Mineral  Oils  in  Fatty  Animal  or  Vegetable  Oils,  and 
vice  versa. — The  distinction  of  coal  oil  from  animal  and  vegetable  oil 
is  not  very  difficult,  from  the  fact  that  mineral  oils  cannot  be  saponi- 
fied, as  the  following  experiment  will  show.  Boil  the  oil  with  caustic 
soda  liquor  until  it  is  saponified  ;  the  soap  resulting  from  it  is  to  be 
evaporated  in  a  water  bath,  and  the  residue  treated  with  ether  or  pe- 
troleum spirit.  The  soap  will  be  insoluble,  while  the  coal  oil,  if  such 
was  mixed  with  the  oil  to  be  tested,  will  be  soluble  in  the  ether  or  pe- 
troleum spirit.    The  latter  is  to  be  evaporated  carefully  in  a  gradu- 
