ON  A  NEW  METHOD  OF  PREPARING  CAFFEIN. 
233 
water,  prevents  the  alkaloid  from'  crystallizing,  and  thus  renders 
it  impossible  to  extract  the  whole  of  the  caffeine  from  the  coffee. 
The  author,  therefore,  tried  the  following  method.  He  brought 
the  decoction  of  coffee  to  the  consistence  of  an  extract,  and  treated 
it  with  alcohol,  which  left  undissolved  a  resinous  substance  of 
the  appearance  of  bird-lime  ;  he  then  dissolved  a  slight  excess  of 
pulverized  caustic  lime  in  the  alcoholic  fluid,  which,  when  filtered 
and  evaporated  to  the  necessary  degree,  furnished  crystallized, 
but  still  impure  caffein.  This  was  pressed  between  thick  linen, 
to  get  rid  of  the  adherent  mother  liquor,  and  then  dissolved  in 
well  water  and  treated  with  animal  charcoal,  by  which  means 
the  alkaloid  was  obtained  in  a  very  pure  state.  This  mode  of 
preparation  gave  one-twentieth  of  an  ounce  of  caffein  to  every 
pound  of  coffee,  or  twice  as  much  as  by  the  ordinary  process. 
As  coffee  is  pulverized  with  difficulty,  and  does  not  contain  very 
much  of  the  bitter  principle,  the  author  substituted  tea  for  coffee  ; 
tea  being  richer  in  caffein,  furnishes  this  alkaloid  with  more 
facility  and  in  greater  quantity. 
Although,  by  this  treatment,  tea  furnishes  a  larger  quantity 
of  the  product,  it  is  certain  that  the  action  of  the  alcohol  upon 
the  extract  of  tea  is  attended  with  difficulty,  on  account  of  the 
very  large  quantity  of  insoluble  matter  which  it  leaves  ;  this  not 
only  renders  the  process  inconvenient,  but  may  also  lead  to  a 
diminution  of  the  result,,  as  indeed  the  author  found  to  be  the 
case.  He  therefore  changed  the  mode  of  preparation  in  the  fol- 
lowing manner. 
He  exhausted  the  tea  by  decoction,  mixed  the  fluids  obtained, 
and  concentrated  them  at  first  with  a  strong  heat.  When  the 
fluid  was  somewhat  thickened,  he  put  it  into  a  porcelain  dish, 
and  evaporated  it  by  a  gentle  heat  to  the  consistence  of  a  thick 
extract.  To  this  extract,  whilst  still  warm,  he  added  two  oz.  of 
finely-powdered  commercial  pearlash  for  every  pound  of  tea ; 
this  was  stirred  in  with  a  wooden  spatula.  The  alkaline  car- 
bonate produced  a  strong  effervescence  ;  the  mass  swelled  up,  but 
returned  to  its  original  volume  at  the  completion  of  the  reaction. 
The  dish  was  then  removed  from  the  fire,  and  its  contents  treated 
with  alcohol ;  this  may  be  effected  in  two  ways.  The  alcohol 
may  be  added  to  the  substance  just  taken  from  the  fire,  and 
stirred  with  a  pestle  of  glass  or  earthenware,  which  may  be 
