Am.  Jour.  Pharm.  > 
Aug  1,  1874.  J 
Test  for  Alkaloids. 
375 
author  gives  the  details  of  several  alternative  processes,  but  for 
various  reasons  adopts  the  following  as  the  most  convenient : 
Take  of— 
Subnitrate  of  Bismuth      .  1-50  grams. 
Iodide  of  Potassium         .        .       .        .  r00  " 
Hydrochloric  Acid  ....  20  drops. 
Water   20  grams. 
The  subnitrate  is  suspended  in  water  and  boiled,  and  the  alkaline 
iodide  and  the  acid  are  then  added.  A  limpid  solution  is  thus 
obtained  of  very  fine  orange-yellow  color,  which  may  be  readily  used 
as  a  test  for  alkaloids. 
If  one  drop  of  this  solution  be  poured  into  water,  a  white  precip- 
itate is  produced,  resulting  from  the  decomposition  of  the  salt  by  the 
water.  This  decomposition  may  be  avoided  by  the  addition  of  a  few 
drops  of  an  acid,  the  author  preferring  hydrochloric  acid  for  the  pur- 
pose. It  is  not  indifferent  whether  the  acid  be  added  to  the  reagent 
or  to  the  solution  to  be  tested  for  an  alkaloid  ;  four  drops  of  hydro- 
chloric added  to  40  or  50  c.c.  of  the  latter  being  sufficient  to  prevent 
the  decomposition,  but  a  much  larger  quantity  is  required  if  added  to 
the  iodide  reagent. 
If  the  solution  be  not  sufficiently  acid,  the  decomposition  takes 
place  after  some  minutes,  instead  of  occurring  immediately.  But  the 
more  or  less  deep  orange-yellow  precipitate  resulting  from  the  pres- 
ence of  an  alkaloid  may  be  confounded  with  the  pale  yellow  product 
of  the  decomposition  of  the  iodide  by  water. 
Prepared  in  the  above  manner,  this  reagent  deposits  after  some 
time  a  blackish  powder  which  is  easily  recognized  as  iodide  of  bis- 
muth, and  may  be  removed  by  filtration. 
The  alkaloid  precipitate  does  not  appear  to  present  a  constant 
composition,  it  seeming  to  vary  according  to  the  proportion  of  acid 
present  in  the  solution.  Thus,  for  example,  in  precipitating  quinia 
from  a  solution  of  its  sulphate,  if  only  sufficient  acid  be  added  to  pre- 
vent the  decomposition,  a  beautiful  orange-red  precipitate  is  obtained  ; 
but  if  there  be  an  excess  of  acid,  the  precipitate  is  paler  and  dimin- 
ished in  volume. 
Since,  therefore,  the  nature  of  the  precipitate  varies,  and  the  com- 
position of  the  reagent  itself  also  changes,  M.  Yvon  considers  it 
would  be  impossible  to  use  the  double  iodide  of  bismuth  and  potas- 
