MEANS  OF  DETECTING  PICRIC  ACID. 
525 
of  nitric  acid  during  the  combustion  of  hydrogen  in  ordinary  air. 
— Pharm.  Journ.,  Sept.  1853,  from  the  Jahrbuch  der  k.  k. 
geologischen  Heichsanstalt,  Jahrg.  I.,  No.  2. 
ON  THE  MEANS  OF  DETECTING  PICRIC  ACID  IN  BEER. 
By  M.  J.  L.  Lassaigne. 
It  was  stated  about  a  year  ago,  in  the  Journal  de  Chimie 
Medieale,  that  picric  acid  was  sometimes  used  as  a  substitute  for 
part  of  the  hops  in  the  manufacture  of  beer.  This  adulteration, 
which  has  been  adopted  in  some  localities,  cannot  be  tolerated, 
and  it  was  with  the  view  of  putting  a  stop  to  such  a  practice  that 
the  following  experiments  were  made. 
The  bitter  taste  of  picric  acid,  which  has  the  same  character 
as  that  of  the  hop,  cannot  be  distinguished  by  the  taste  from  the 
latter  when  contained  in  beer,  as  I  have  satisfied  myself  by  direct 
experiment ;  but  its  presence  may  be  detected  by  some  simple 
chemical  reactions. 
In  studying  the  properties  of  picric  acid,  I  have  observed  that 
this  acid,  which  communicates  its  color  and  bitterness  to  water, 
when  dissolved  in  beer  is  not  precipitated  by  subacetate  of  lead, 
while  the  bitter  principle  and  the  color  of  the  hop  are  almost  en- 
tirely removed  by  that  reagent.  I  have  also  observed  that  animal 
charcoal,  whether  purified  or  not,  is  capable  of  absorbing  and  re- 
moving the  coloring  matter  of  beer,  while  picric  acid  is  unacted 
upon  by  it,  the  liquor  retaining  its  original  color  unaltered  by 
the  charcoal. 
It  is  on  the  properties  possessed  by  these  two  reagents  that  I 
have  founded  the  means  of  detecting  small  quantities  of  picric 
acid  when  added  to  beer. 
In  the  experiments  I  have  made  on  this  subject  I  have  operated 
on  pure  beer  of  good  manufacture,  and  on  some  to  which  I  have 
added  one  twelve  thousandths  and  even  one  eighteen  thousandths 
of  picric  acid.  On  adding  to  both  samples  an  excess  of  tribasic 
acetate  of  lead,  or  agitating  them  with  excess  of  animal  charcoal, 
the  pure  beer  is  almost  completely  decolorized,  while  that  con- 
taining the  picric  acid  in  the  proportions  mentioned,  retains  a 
citron  yellow  color  in  consequence  of  the  picric  acid  not  being 
removed. 
