Am7a0nU"'I87h9a.rm'}  Tannin  and  Bitter  Principle  of  Hops.  2 
TANNIN  AND  BITTER  PRINCIPLE  OF  HOPS. 
By  C.  Etti. 
The  substance  named  "lupulo-tannic  acid"  by  the  author  does  not 
precipitate  gelatin  ;  if,  however,  it  is  dried  at  120°  to  I30°C,  it  changes 
from  yellowish-white  to  red,  loses  water,  and  when  dissolved  in  very 
dilute  alcohol  precipitates  gelatin  completely,  just  like  ordinary  tannin. 
On  heating  the  yellowish  alcoholic  solution  of  the  original  tannin  on 
the  water-bath  it  becomes  red,  and  on  evaporation  a  dark-red  residue 
remains  which  also  precipitates  gelatin  when  again  dissolved  in  dilute 
alcohol.    The  author  calls  this  "  phlobaphen." 
Analysis  gives  the  same  composition  for  this  as  for  the  red  com- 
pound obtained  by  heating  the  lupulo-tannic  acid  at  120°  to  1300,  each 
having  the  formula  C50H46O25,  and  they  may  be  supposed  to  result  from 
the  expulsion  of  a  molecule  of  water  from  two  molecules  of  tannic 
acid  of  the  formula  C25H24013. 
The  coarsely  powdered  hop  flowers  are  placed  in  an  extraction 
apparatus,  and  after  being  freed  fiom  resin  and  bitter  principle  as  much 
as  possible,  the  mass  is  extracted  with  20  per  cent,  alcohol.  On 
evaporating  to  a  small  bulk  and  cooling  a  red  precipitate  of  phlobaphen 
is  formed ;  this  is  dissolved  in  90  per  cent,  alcohol,  evaporated  ta 
dryness  and  heated  to  1200  or  1300.  If  it  tastes  bitter,  the  bitter 
principle  may  be  removed  by  ether.  Phlobaphen  is  easily  soluble  in 
alkalies,  and  is  precipitated  unchanged  by  dilute  mineral  acids.  On 
boiling  the  freshly  precipitated  and  not  previously  heated  phlobaphen 
with  dilute  mineral  acids  it  is  decomposed,  glucose  and  one  molecule  of 
water  being  split  off. 
As  the  phlobaphen  is  easily  prepared,  is  constant  in  composition  and 
precipitates  gelatin  solution  completely,  it  may  be  estimated  quantita- 
tively like  tannin  and  may  be  used  in  standardizing  the  solution 
employed. 
An  etherial  extract  of  hop  flowers  contains,  besides  an  essential  oil, 
chlorophyll,  a  crystallized  white  and  an  amorphous  brown  resin,  to  which 
the  bitter  principle  adheres.  After  driving  off  the  ether  90  per  cent, 
alcohol  dissolves  brown  resin  and  the  bitter  principle,  which  may  be 
separated  from  each  other  by  adding  water  as  long  as*  the  resin  con- 
tinues to  be  precipitated.  Repeated  solution  in  alcohol  and  dilution 
with  water  frees  the  resin  from  the  bitter  principle.  The  aqueous 
solution  is  evaporated  in  a  vacuum  over  sulphuric  acid,  tile  amorphous 
