^S'.mlT'}    Separation  of  Mixed  Alkaloids,  etc.  501 
When  all  the  liquid  has  passed  through  the  filter,  the  powder  remain, 
ing  on  the  filter  is  washed  with  100  cubic  centimetres  of  alcohol,  so 
that  in  the  whole  400  cubic  centimetres  of  alcohol  are  used  for  20 
grammes  of  bark.  The  united  liquors  are  now  slightly  acidulated 
with  weak  sulphuric  acid,  whereby  a  precipitate  of  sulphate  of  lime 
is  formed.  After  this  has  subsided  the  greater  part  of  the  liquor 
can  be  poured  off,  the  rest  being  filtered  through  a  small  filter.  The 
clear  liquid  is  now  distilled  to  obtain  the  greater  part  of  the  spirit 
used,  and  the  remaining  liquid  poured  into  a  capsule,  to  which  is 
added  the  spirit  and  the  water  by  which  the  distilling  apparatus  is 
subsequently  washed.  The  capsule  is  now  heated  on  a  water-bath 
till  all  the  spirit  has  been  expelled,  and  the  remaining  liquor  which 
contains  all  the  alkaloids  in  the  form  of  acid  sulphates,  is,  after  cool- 
ing, filtered  through  a  small  filter.  On  the  filter  remains  a  mixture 
of  quinovic  acid  and  fatty  substances,  which  must  be  washed  repeat- 
edly with  water  slightly  acidulated  by  sulphuric  acid  till  caustic  soda 
no  longer  produces  any  turbidity  in  the  passing  liquid.  The  filtrate 
is  now  reduced  to  a  small  volume  by  heating  on  a  water-bath,  and 
while  still  warm  precipitated  by  a  slight  excess  of  caustic  soda.  The 
benefit  derived  from  this  kind  of  precipitation  is  that  the  alkaloids 
precipitated  from  a  warm  solution  are  less  voluminous,  and  can, 
therefore,  more  easily  be  washed.  The  drawback,  however,  is  that 
the  alkaloids  from  some  barks  melt  under  these  circumstances,  which 
drawback  can,  however,  easily  be  rectified  by  powdering  carefully  the 
alkaloids  after  the  cooling  of  the  liquor,  and  collecting  this  powder 
on  a  small  filter.  After  washing  with  the  smallest  possible  quantity 
of  distilled  water,  sufficient  to  remove  the  soda  salt  but  not  to  dis- 
solve quinine,  the  filter  is  laid  upon  blotting  paper,  and  this  so  often 
renewed  till  the  mixed  alkaloids  can  easily  be  separated  from  the 
filter  without  adhering  to  it,  which  can  be  done  before  they  are  en- 
tirely dry,  but  requires  some  practice.  They  are  then  heated  in  a 
weighed  capsule  on  the  water-bath,  till  repeated  weighings  show  that 
the  weight  remains  constant.  The  observed  weight  multiplied  by  five 
gives  the  amount  of  mixed  alkaloids  in  100  parts  of  bark. 
The  amount  of  quinovic  acid  can  be  ascertained  in  the  meantime, 
if  the  mixture  of  quinovic  acid  and  fatty  substances  be  treated  with 
a  weak  solution  of  caustic  soda,  by  which  a  great  part  of  this  mix- 
ture is  dissolved.  If  to  this  turbid  solution  a  slight  excess  of  chlo- 
ride of  calcium  is  added,  only  the  quinovate  of  lime  remains  in  solu- 
