356 
Testing  of  Olive  Oil. 
J  Am.  Jour.rharm, 
1      July,  1883. 
For  testing  the  solubility  of  the  fatty  acids  in  alcohol-acetic  acid^ 
the  method  proposed  by  David  ^  for  the  estimation  of  stearic  acid  is 
applied. 
The  principle  of  this  method  consists  therein  that  when  acetic  acid 
is  added  by  drops  to  an  alcoholic  solution  of  oleic  acid  a  moment 
occurs  when  the  oleic  acid  becomes  perfectly  separated^  but  that  stearic 
acid,  which  is  insoluble  in  a  mixture  of  alcohol  and  acetic  acid,  also 
remains  insoluble  when  the  mixture  contains  oleic  acid.  In  order, 
therefore,  to  apply  the  stated  method  for  the  testing  of  olive  oil,  the 
following  manipulations  are  to  be  performed :  Equal  parts  of  glacial 
acetic  acid  and  water  are  mixed  together  in  a  flask ;  furthermore,  into 
a  small  tube,  divided  into  ^-^  ccm.,  are  brought  1  ccm.  pure  oleic  acid, 
3  ccm.  of  alcohol  of  95  per  cent.,  and  2  ccm.  acetic  acid.  Hereby 
nothing  should  be  separated ;  but  if  an  additional  ccm.  of  acetic 
acid  is  added  a  turbidity  begins  to  occur,  and  when  there  floats  upon 
the  mixture  of  alcohol  and  acetic  acid  1  ccm.  of  oleic  acid  (or  at  first 
more)  the  liquid  is  ready  for  application.  If  this  is  not  the  case,  the 
proportions  are  varied  until  the  object  is  attained  that,  by  the  addition 
of  yL-  ccm.  acetic  acid  a  complete  separation  takes  place.  If  this  is 
attained,  alcohol  and  acetic  acid  are  then  mixed  in  the  proportions 
indicated  by  this  preliminary  experiment,  e.  g.,  300  alcohol  and  225 
acetic  acid.  To  the  alcohol-acetic  acid  from  1  to  2  grams  of  stearic 
acid  are  then  added,  and  the  supernatant  clear  solution  employed  for 
the  experiment.  Of  the  oil  (acids)  to  be  tested  1  ccm.  is  first  placed 
in  the  tube,  15  ccm.  of  alcohol-acetic  acid  added,  the  mixture  actively 
agitated,  and  the  whole  allowed  to  repose  at  a  temperature  of  15°C. 
If  the  olive  oil  is  pure,  it  dissolves  to  a  perfectly  clear  liquid,  and  the 
solution  also  retains  this  character.  Cotton  seed  oil  is  insoluble,  and 
the  solution  obtained  by  gently  Avarming  solidifies  at  15°C.  to  a  white 
jelly.  Sesame  oil  and  ground  nut  oil  show  a  similar  behavior.  Sun- 
flower oil  dissolves,  but  separates  at  15°C.  a  granular  precipitate. 
Rape  seed  oil  is  perfectly  insoluble,  and  floats  as  an  oily  layer  upon 
the  surface.  Ricinus  oil,  on  the  contrary,  is  soluble  to  a  clear  liquid, 
precisely  like  olive  oil,  and  can  therefore  not  be  detected  in  olive  oil 
by  this  method.  For  the  recognition  of  ricinus  oil,  beside  the  direct 
testing  of  the  oil  with  alcohol,  the  determination  of  the  melting  point 
of  the  acids  is  of  service. 
Olive  oil  with  25  per  cent,  of  cotton  seed  oil  separates  a  granular 
1  "  Compt.  Rend.,"  1878,  p.  1416. 
