In  using,  0.05  gram  or  one  drop  of  the  substance  to  be  tested  is  added
to  5  cc.  of  the  solution.  The  appearance,  after  two  minutes,  of  a  distinct
pink,  red,  purple,  or  blue  coloration  indicates  the  presence  of  an  aldehyde*


1919]  DECX)MPOSITION  POINT  OF  EDIBLE  FATS  481

The  test  to  be  of  value  must  be  applied  under  carefully  regulated  con-
ditions. The  reagent  is  reddened  by  alkalis,  by  heating,  or  by  long
exposure  to  air  at  ordinary  temperatures.
The  method.  Having  found  a  suitable  reagent,  the  problem  was
snnply  one  of  bringing  the  fxrnies  into  contact  with  it.  A  test  paper
held  in  the  fumes  was  first  tried.  This  was  unsatisfactory  because  the
paper  was  reddened  merely  by  the  heat.  A  method  was  finally  devised
whereby  the  fumes  from  the  heating  fat  could  be  drawn  through  a
U-tube  containing  the  reagent.
The  apparatus.  The  first  apparatus  used  consisted  of  a  wide  mouthed
flask,  having  a  capacity  of  125  cc.  and  a  diameter  of  2\  inches,  which
was  fitted  with  a  cork  carrying  (1)  a  thermometer,  (2)  a  capillary  tube
to  admit  air  above  the  surface  of  the  fat,  and  (3)  a  bent  delivery  tube.
The  delivery  tube  was  connected  with  the  U-tube  holding  the  reagent
and  the  latter  with  a  small  filter  pimip.  The  latter  was  adjusted  so
that  air  and  fumes  from  above  the  fat  were  drawn  through  the  U-tube
at  a  constant  but  not  a  rapid  rate,  so  that  the  bubbles  passed  slowly
through  the  reagent.  The  slightest  color  in  the  U-tube  was  regarded
as  the  end  point.
