426 
ALKALOIDS  IN  THE  CINCHONA  BARKS. 
valuable  salts.  Even  very  slight  traces  of  the  foreign  alka- 
loids which  escape  detection  by  the  ether  method,  may  be  rec- 
ognized in  the  solution  by  the  opalescence  of  the  mixture,  pro- 
vided the  experiment  is  properly  carried  out. 
2.  Test  Fluid. — If  Liq.  ammonise  of  the  strength  ordered  in 
the  London  Pharmacopoeia,  that  is,  of  sp.  gr.  0-960,  is  at  hand, 
it  may  serve  as  a  test-fluid ;  it  is  more  accurate  and  safe,  how- 
ever, to  standardize  an  ammonia  solution  of  unknown  strength 
by  means  of  a  standard  solution  of  sulphate  of  quinine  saturated 
in  the  cold,  and  of  known  purity. 
3.  Preparation  of  the  Solution  of  Sulphate  of  Quinine  re. 
quired  for  Analysis. — It  is  especially  necessary  that  the  dis- 
tilled water  employed  should  not  be  warmer  than  15°  C,  since 
the  sulphate  of  quinine  is  considerably  more  soluble  in  water 
which  is  only  a  few  degrees  above  that  temperature.  Water  pos- 
sessing this  temperature  is  easily  obtained  both  in  summer  and 
winter  ;  if  above  that  temperature,  it  must  be  cooled  down  by 
placing  the  vessel  containing  the  quinine  salt  into  fresh  spring 
water.  From  two  to  four  grammes  of  the  sulphate  (which  must, 
of  course,  be  neutral)  are  agitated  in  a  small  beaker  with  20  to 
40  c.  c.  of  distilled  water  till  they  are  dissolved  to  a  pasty  fluid. 
After  digesting  for  about  half  an  hour,  the  whole  is  thrown  on 
a  small  filter,  either  of  paper  or  linen,  and  squeezed,  and  the  so- 
lution thus  obtained  again  filtered  till  it  is  obtained  perfectly 
clear. 
4.  Qualitative  method. — 5  c.  c.  of  this  solution  of  sulphate  of 
quinine  are  measured  out  into  a  dry  test-tube,  then  treated  with 
5  c.  c.  of  the  standard  solution  of  ammonia  of  sp.  gr.  0-92,  or 
with  7  c.  c.  of  a  standard  solution  of  ammonia  of  0-96  sp.  gr., 
or  also  with  a  corresponding  number  of  c.  c.  of  a  standard  solu- 
tion of  ammonia  of  different  sp.  gr.,  so  as  to  prevent  the  two 
layers  of  liquid  from  mixing  at  first  as  little  as  possible.  The 
test-tube  is  then  closed  with  the  thumb,  and  the  liquid  made  to 
run  repeatedly  backward  and  forward,  whereby  the  mixture  will 
be  found  to  have  become  perfectly  clear  and  free  from  sus- 
pended alkaloid,  or  will  become  so  after  a  few  minutes.  Violent 
agitation  of  the  liquid  in  the  test-tube  is  objectionable,  because 
ammonia  gas  is  liberated,  and  would  render  the  reaction  inaccu- 
rate.    Should  the  experiment  give  a  doubtful  result, — that  is, 
