VARIETIES. 
375 
pressed  powerfully  to  remove  the  mother-liquor.    These  crystals  were  re- 
dissolved  in  a  small  quantity  of  water,  the  solution  evaporated,  and  crystal- 
lized anew.    It  gave  almost  nothing  but  caffeine,  in  long  silky  white  needles, 
with  little  or  no  color.    The  proportion  of  caffeine,  obtained  in  five  experi- 
ments, made  upon  different  samples  of  coffee,  was  as  follows : — 
Caffeine  in  raw  coffee. 
In  Native  Ceylon        .        .        .        0.80  per  cent. 
«  0.80  " 
«       u  tt  ...  1.01  " 
*  Plantation  Ceylon       ,        .        .    0.54  " 
«  "...        0.83  « 
The  caffeine  of  the  wild  coffee  appears  to  exceed  that  of  the  cultivated 
plant ;  the  mean  proportion  of  caffeine  in  Native  Ceylon  being  0.87  percent., 
and  in  Plantation  Ceylon  0.69  per  cent. 
The  mean  average  of  the  whole  five  samples  is  0.80  per  cent,  of  caffeine. 
Probably  the  actual  quantity  of  caffeine  in  the  coffee-bean  is  from  0.75  to 
one  per  cent.,  allowance  being  made  for  losses  in  the  separation. 
The  proportion  of  theine  (or  caffeine)  in  tea  is  considerably  greater,  and 
more  easily  extracted.  Two  pounds  of  fine  strong  Congou  yielded  293 
grains  of  theine,  or  2.09  per  cent. 
When  it  is  merely  desired  to  extract  caffeine  from  raw  or  roasted  coffee, 
without  reference  to  quantity,  the  general  process  for  the  extraction  of  or- 
ganic bases  by  means  of  ether  suffices.  Lime  is  added  to  the  infusion  of 
coffee,  which  is  then  evaporated  to  dryness  upon  a  water-bath.  The  extract 
may  be  divided  by  means  of  clean  sand,  and  then  agitated  with  ether.  The 
caffeine  crystallizes  as  the  ether  evaporates,  or  it  may  be  re-dissolved  in 
water,  and  crystallized  again.  We  believe  that  the  caffeine  from  ten  per 
cent,  of  coffee  in  a  mixture  might  be  extracted  in  sufficient  quantity  for  its 
identification  by  the  preceding  simple  process.  Caffeine,  when  once  obtained, 
is  fully  recognized  by  its  easy  sublimation,  and  also  by  its  action  with  nitric 
acid,  in  which  it  resembles  uric  acid.  When  the  solution  of  caffeine  in 
nitric  acid  is  evaporated  to  dryness,  and  exposed  to  ammoniacal  gas  it  is 
covered  by  a  pink  blush,  like  murexide. 
The  only  substances  besides  coffee  in  which  caffeine  is  known  to  exist, 
are  tea,  Paraguay  tea,  and  a  species  of  chocolate  made  from  the  Guarana 
officinalis  or  Paullinia  sorbilis. 
11.  Chemists  generally  are  disposed  to  refer  the  flavor  and  peculiar  pro- 
perties of  coffee,  as  a  beverage,  more  to  its  acid — the  caffeic  acid  (particu- 
larly after  that  substance  is  modified  in  its  properties  by  roasting),  than  to 
any  other  constituent  of  the  seed.  Rochleder  considers  this  acid  as  belong- 
ing to  the  tannin  class  of  substances,  and  calls  it  tanno-caffeic  acid.  But 
as  caffeic  acid  does  not  precipitate  gelatine,  it  is  deficient  in  the  most  char- 
acteristic quality  of  the  tannic  acids.  Caffeic  acid,  in  the  present  state  of 
our  knowledge,  appears  to  be  confined  to  the  coffee-plant. 
