308  The  Influence  of  Oxygen  on  Olive  Oil.     { Am7u7y^?<£arm 
THE  INFLUENCE  OF  OXYGEN  AND  OF  NITROGEN, 
AND  SUNLIGHT  AND  DARKNESS  ON  OLIVE  OIL  AS 
AFFECTING  THE  IODINE  AND  SAPONIFICATION 
NUMBERS  AND  THE  PRODUCTION  OF  RANCIDITY. 
By  Lbon  A.  Ryan, 
Assistant  Demonstrator  of  Chemistry, 
and 
John  Marshall, 
Professor  of  Chemistry  and  Toxicology. 
[From  the  Robert  Hare  Laboratory  of  Chemistry,  Department  of  Medicine,  University  of 
Pennsylvania.] 
The  variations  of  the  iodine  and  saponification  numbers  of  olive 
oil  have  led  us  to  examine  into  the  influence  of  such  factors  as  oxy- 
gen, nitrogen,  direct  sunlight,  diffused  sunlight  and  darkness  as 
affecting  the  analytical  constants  and  at  the  same  time  their  influ- 
ence upon  the  production  of  rancidity.  The  variations  are  fairly 
large  and  may  possibly  be  attributed  to  the  length  of  time  the  oil 
has  been  exposed  to  the  action  of  the  oxygen  of  the  air.  As 
examples  of  variations  it  may  be  cited  that  v.  Hiibl1  found  on 
examining  twenty  specimens  of  olive  oil  that  the  iodine  number 
ranged  between  8r6  and  84-5.  Negri  and  Fabris2  as  a  result  of 
the  examination  of  one  hundred  specimens  of  olive  oil  found  the 
maximum  iodine  number  to  be  88.  Sherman3  gives  the  range  of 
iodine  number  as  being  between  78-90,  and  the  saponification  num- 
ber between  186-196.  Wiley4  states  that  when  the  iodine  number 
is  above  89  or  90  there  may  be  suspicion  of  the  oil  having  been 
adulterated.  Sherman  and  Falk5  examined  a  specimen  of  fresh 
olive  oil  and  found  the  iodine  number  to  be  83-8,  and  the  same 
oil,  after  standing  several  months,  with  occasional  shaking,  in  an 
uncorked  bottle,  loosely  covered  to  exclude  dust,  and  frequently 
exposed  to  direct  sunlight,  yielded  an  iodine  number  of  77-4,  thus 
showing  that  exposure  to  air  and  sunlight  acts  on  the  oil  with  the 
effect  of  decreasing  the  iodine  number.    Ulzer  and  Klimont6  give 
1  V.  Hiibl,  Benedikt-Ulzer,  Analyse  d.  Fette  u.  Wachsarten,  p.  690. 
2  Negri  and  Fabris,  Zeit.  f.  Analyt.  Chemie,  1894,  p.  548. 
3  Sherman,  Organic  Chemistry.    Macmillan  Co.,  1905,  p.  147. 
4  Wiley,  Foods  and  their  Adulterations.    Blakiston  &  Co.,  1907,  p.  403. 
5  Sherman  and  Falk,  Journ.  Amer.  Chem.  Soc,  July,  1903,  p.  713. 
6  Ulzer  und  Klimont,  Chemie  d.  Fette.    Jul.  Springer,  1906,  p.  289. 
