ON  THE  DRIED  COFFEE-LEAF  OF  SUMATRA. 
251 
1.031  grm.  gave  0.153  platinum  =  1.70  nitrogen  per  cent. 
From  these  results  it  is  clear  that  dried  coffee-leaves  are  some- 
what richer  in  theine  than  the  coffee-bean,  and  contain,  as  nearly 
as  may  be,  the  same  amount  of  that  principle  as  Paraguay  tea. 
From  the  violent  roasting  to  which  the  coffee-leaves  had  been  sub- 
jected, I  feel  convinced  a  portion  of  their  theine  has  been  dissipated; 
and  were  they  only  dried  at  a  moderate  temperature,  I  confidently 
expect  that;  they  would  yield  1 J  per  cent,  of  theine.  The  theine 
obtained  from  the  coffee-leaves  was  not  subjected  to  analysis. 
This  I  considered  unnecessary,  as  it  possessed  all  the  well-known 
properties  of  ordinary  theine,  crystallizing  in  fine  silky  crystals, 
which  readily  sublimed  when  heated ;  and  when  digested  with 
nitric  acid  and  cautiously  evaporated  to  dryness,  they  gave  when 
treated  with  ammonia  the  characteristic  red  coloration  so  closely 
resembling  that  from  uric  acid  when  acted  on  by  the  same  reagents. 
With  regard  to  caffeic  acid,  the  other  characteristic  proximate 
principle  of  coffee,  the  leaf  of  the  coffee  plant  contains  it  also  in 
larger  quantity  than  the  berry.  Caffeic  acid  is  precipitated  of  a 
deep  yellow  color  by  acetate  of  lead,  but  is  apparently  uncrystal- 
lizable  ;  at  least  the  numerous  attempts  which  I  have  made  to 
obtain  it  in  a  crystallizable  state  have  hitherto  proved  unsuccess- 
ful. Caffeic  acid  does  not  precipitate  solutions  of  gelatine,  and 
it  is  therefore  not  a  species  of  tannin,  as  has  been  sometimes 
asserted.  The  most  remarkable  property  of  caffeic  acid  is  that 
first  stated  at  the  34th  page  of  the  joint  Report  on  the  adultera- 
tion of  coffee  already  quoted.  "  Caffeic  acid  appears  to  be  analo- 
gous to  kinic  acid,  the  acid  of  cinchona  barks,  for  it  yields  kinone 
when  oxidated  by  means  of  sulphuric  acid  and  binoxide  of  man- 
ganese. To  observe  this  properly,  the  coffee  is  boiled  with  water 
and  a  little  slaked  lime,  the  infusion  filtered  and  evaporated  down 
to  the  consistence  of  a  syrup.  The  syrupy  liquid  is  then  mixed 
in  a  retort  with  four  times  its  weight  of  binoxide  of  manganese, 
and  one  part  of  oil  of  vitriol  diluted  with  an  equal  bulk  of  water. 
Sufficient  heat  is  produced  by  the  action  of  the  sulphuric  acid 
upon  the  other  materials  to  bring  over  the  greater  portion  of  the 
kinone,  and  the  lamp  need  not  be  applied  till  towards  the  close  of 
the  operation.  The  distillate  consists  of  yellow  crystals  of  kinone, 
which  usually  coat  the  neck  and  sides  of  the  retort,  and  a  bright 
yellow  liquid,  which  is  a  saturated  aqueous  solution  of  kinone, 
