AmMa°rch  ^gig"1'  }  Determination  of  Vanillin  in  Vanilla  Extract.  169 
excess  removed  from  the  filtrate  by  hydrochloric  acid  before  adding 
thiobarbituric  acid.  The  results  are  in  close  agreement  with  the 
other  results,  showing  that  the  small  amount  of  lead  chloride  re- 
maining in  solution  does  not  interfere  with  the  determination. 
A  sample  of  vanilla  extract  of  known  purity  was  next  used.  The 
procedure  was  as  follows : — 25  Cc.  of  the  extract  were  dealcoholized 
in  the  usual  manner,  then  transferred  to  a  50  Cc.  standard  sugar 
flask  and  rilled  to  the  mark  with  lead  acetate  solution.  After  stand- 
ing for  several  hours  at  about  370  C.  the  contents  of  the  flask  were 
filtered  through  a  dry  filter.  The  filtrate  was  a  straw  color,  indicat- 
ing the  absence  of  caramel  as  added  coloring  matter.  40  Cc.  of 
this  filtrate  was  then  transferred  to  another  50  Cc.  flask.  Sufficient 
concentrated  hydrochloric  acid  was  added  to  bring  the  volume  to 
50  Cc.  and  the  acidity  to  12  per  cent.  After  standing  a  few  minutes 
the  lead  chloride  was  removed  by  filtration  through  a  dry  filter  and 
40  Cc.  of  the  filtrate  taken  for  the  determination.  On  adding 
thiobarbituric  acid  in  12  per  cent,  hydrochloric  acid  solution,  an 
orange-colored  precipitate  resulted,  indistinguishable  in  color  from 
the  product  with  pure  vanillin.  However,  the  color  of  the  filtrate 
was  somewhat  darker  than  with  vanillin  alone,  due  no  doubt  to 
the  original  color  of  the  filtrate  after  clarification.  The  precipitate 
was  allowed  to  stand  over  night  filtered  on  a  Gooch  crucible,  washed 
with  hydrochloric  acid  and  water  as  in  the  previous  determination 
and  dried  at  980.    The  results  were  as  follows: 
Vanilla  Ex- 
tract Taken, 
Cc. 
Aliquot  Per 
Cent,  of  Ex- 
tract Taken. 
Wt.  of  Pre- 
cipitate, G. 
Wt.  of  Precipi- 
tate Corrected 
for  Solubility. 
Vanillin  found 
in  Aliquot. 
Vanillin  in 
25  Cc.  Ex- 
tract, G. 
Vanillin  in  . 
Extract 
Per  Cent. 
25 
64 
.0450 
.0476 
.0260 
.0406 
O.16 
25 
64 
.0450 
.0476 
.0260 
.0406 
O.16 
25 
72 
.0501 
.0527 
.0288 
.0400 
O.16 
25 
72 
.0498 
■0523 
.0286 
•0397 
O.16 
25 
72 
.0510 
.0536 
.0293 
.0407 
O.16 
25 
72 
.0501 
.0527 
.0288 
.0400 
O.16 
25 
72 
.0502 
.0528 
.0289 
.0401 
O.16 
25  + 
80 
.0890 
.0916 
.0501 
.0626 
O.25 
25  + 
80 
.0882 
.0908 
.0496 
.0621 
O.25 
The  above  method  is  not  applicable  to  artificial  extracts  where 
caramel  is  added  as  a  coloring  matter,  since  caramel  contains  fur- 
fural derivatives  which  react  with  thiobarbituric  acid.  The  absence 
of  caramel  should  first  be  demonstrated  qualitatively.  When  cara- 
mel is  present,  the  filtrate  after  clarification  is  brown  instead  of 
