Am"/uOiy?i907arm'}        A  Note  on  a  Source  of  Error.  315 
nitrogen  were  kept  in  the  light  and  in  the  dark  and  the  atmosphere 
of  nitrogen  in  the  flasks  was  saturated  with  water  vapor  and  under 
these  conditions  the  oil  did  not  become  rancid.  The  fact  that  no 
rancidity  was  produced  in  the  sterilized  or  unsterilized  oils  in  an 
atmosphere  of  nitrogen  would  exclude  enzymic  action. 
A  NOTE  ON  A  SOURCE  OF  ERROR  IN  THE  USE  OF  A 
CERTAIN  PETROLEUM  ETHER  AS  AN  EXTRACTING 
MEDIUM. 
By  John  Marshau, 
Professor  of  Chemistry  and  Toxicology,  University  of  Pennsylvania. 
When  commercial  p  etroleum  ether  has  been  carefully  re-distilled 
and  the  fraction  between  200  and  500  C.  is  reserved  for  use,  one  is 
of  the  belief  that  no  hydrocarbons  non-volatile  at  room  tempera- 
ture are  contained  in  the  fraction,  and  this  is  usually  demonstrated 
by  evaporating  a  portion  of  the  distillate  at  room  temperature  and 
observing  whether  any  residue  remains.  The  writer  on  obtaining 
this  fraction  from  a  commercial  petroleum  ether  derived  from  the  ' 
Pennsylvania  oil-field  and,  immediately  after  distillation,  evaporating 
200  c.c.  of  the  fraction  at  room  temperature,  found  that  no  residue 
remained,  but  on  permitting  the  remaining  portion  of  the  distillate 
to  stand  thirty  days  at  room  temperature,  exposed  to  diffused  sun- 
light, in  a  stoppered  flask,  with  an  air  space  of  about  a  litre  above 
the  surface  of  the  liquid,  and  evaporating  200  c.c.  of  it  at  room 
temperature  and  then  over  sulphuric  acid,  a  yellowish,  cosmoline- 
like  residue  weighing  0-0072  gramme  remained.  The  remaining 
portion  of  the  fluid  was  re-distilled  at  20°  to  500  C,  and  200  c.c.  of 
the  distillate  on  evaporation  left  no  residue.  What  remained  of  the 
distillate  was  stood  aside  in  a  stoppered  flask,  as  above  described 
for  a  period  of  ten  days.  At  the  expiration  of  the  ten  days  a  por- 
tion amounting  to  200  c.c.  was  evaporated  spontaneously  and  then 
over  sulphuric  acid,  with  the  result  that  a  residue  weighing  0-0007 
gramme  was  left.  On  letting  the  remaining  portion  of  the  distillate 
stand  seventeen  days  and  evaporating  200  c.c.  of  it,  a  residue  of 
00016  remained.  On  making  a  blank  test  with  200  c.c.  of  that 
which  had  stood  seventeen  days  by  using  it  in  a  Soxhlet  extractor 
containing  a  Schleicher  and  Schull  fat-free  paper  thimble  filled  with 
