TESTS  FOR  THE  CINCHONA-ALKALOIDS. 
343 
powder ;  the  mixture  soon  smells  of  iodine.  The  quantities  of 
these  two  precipitates  show  the  proportion  of  oxidized  and  of 
pure  cinchona-tannin. 
4.  Sulphate  of  copper  is  perfectly  indifferent  to  the  aqueous 
infusion  of  bark,  which  contains  no  kinovic  acid,  but  indicates 
the  smallest  proportion  of  this  acid  by  a  dirtyish  green  coloration 
of  the  mixture,  which  is  speedily  followed  by  a  similarly  colored 
fine  powder,  which  is  easily  separated  by  the  filter,  and,  after 
being  washed,  is  distinctly  recognized  by  its  very  bitter  and 
metallic  taste,  as  kinovate  of  copper.  The  more  abundant  this 
precipitate,  the  greater  is  the  proportion  of  kinovic  acid.  All 
other  reagents  hitherto  employed  can  be  absolutely  dispensed 
with. 
Of  all  the  hitherto  known  methods  for  the  quantitative  determi- 
nation of  alkaloids,  I  prefer  the  following : — If  the  quantity  of 
bark  at  command  be  large,  it  is  necessary,  in  the  first  place, 
to  ascertain  whether  it  consist  of  one  or  of  several  sorts.  An 
experienced  eye  can  readily  determine  this.  The  several  sorts 
should  be  separated,  and,  for  experiment,  not  too  small  a  quantity 
selected  from  the  entire  mass  of  the  coated  and  uncoated  of  the 
coarser  and  finer  barks,  taking  of  each  sort  according  to  the 
various  dimensions  in  which  it  is  contained  in  the  whole  mass, 
about  an  equal  weight.  These  pieces  are  to  be  finely  powdered 
and  the  residue  mixed  with  the  powder.  Of  this  powder  500  grs. 
or  1000  grs.  are  to  be  completely  exhausted  by  digestion  in  the 
water-bath,  with  the  necessary  quantity  of  alcohol  of  eighty  per 
cent.  (I  use  six  ounces  of  alcohol  for  1000  grs.  bark ;)  the  cold 
tincture  is  to  be  strained  through  a  thin  but  close  piece  of  linen, 
the  residue  washed  with  alcohol  and  again  digested,  and  com- 
pletely exhausted  with  half  the  weight  of  the  first  employed 
quantity  of  alcohol.  The  residue  which  is  now  obtained  is  to  be 
once  more  exhausted  by  alcohol,  then  dried  and  preserved. 
(There  is  no  occasion  to  spare  the  alcohol  in  this  process,  as  the 
greater  portion  of  it  is  recovered.)  The  united  alcoholic  tinctures 
are  to  be  filtered  and  digested  at  the  common  temperature,  with 
a  mixture  of  equal  parts  by  weight  of  recently  prepared  slacked 
lime  and  of  crude  well-burnt  animal  charcoal,  of  which  in  general 
half  the  weight  of  the  employed  bark  is  required.  The  mixture 
is  to  be  frequently  shaken,  and  the  digestion  continued  until  the 
