268     DETECTION  OF  STRYCHNINE  IN  CASES  OF  POISONING. 
nine  can  always  be  found  in  the  corpse  of  an  individual  poisoned 
by  it. 
1st.  Sensibility  of  the  principal  reagents  on  strychnine : 
Ohromate  of  potash  or  ferridcyanide  of  potassium  and  concentra- 
ted sulphuric  acid. — By  these  reagents  ^QQ0  of  a  grain  of  strych- 
nine can  be  detected,  if  one  drop  of  a  solution,  containing  one 
grain  of  strychnine  in  60,000  grains  of  water,  is  evaporated  in  a 
small  porcelain  dish  on  a  water-bath,  and  the  remaining  sub- 
stance moistened  with  the  smallest  possible  quantity  of  pure  con- 
centrated sulphuric  acid.  By  introducing  in  this  solution  a  very 
small  fragment  of  a  crystal  of  bichromate  of  potash  or  ferridcy- 
anide of  potassium,  and  moving  this  fragment  with  a  glass  rod 
in  the  solution,  a  beautiful  dark  purple  color  is  produced  on  every 
part  of  the  surface  of  the  porcelain  that  has  been  in  contact  with 
the  acid  solution,  and  the  fragment  of  one  of  the  two  salts. 
Bin-iodide  of  potassium,  and  iodide  of  mercury  and  potas- 
sium.— By  a  solution  of  one  of  these  compounds,  ^  of  a  grain 
of  strychnine  can  be  detected.  These  reagents,  like  the  follow- 
ing, possess  only  the  ascertained  sensibility,  provided  the  drop 
of  liquid  is  contained  in  a  capillary  test-tube,  in  which  the  liquid, 
although  only  a  drop,  forms  a  small  column,  in  which  the  forma- 
tion of  a  precipitate  can  be  observed  by  comparison  with  a  simi- 
lar capillary  tube  filled  with  pure  water,  and  mixed  with  the 
reagent. 
Tannic  acid  reveals       of  a  grain  of  strychnine. 
Solution  of  chlorine  in  water, 
Sulphocyanide  of  potassium, 
Neut.al  chromate  of  potash, 
The  precipitate  formed  by  bin-iodide  of  potassium  is  brownish- 
red,  and  if  dissolved  in  weak  warm  spirit,  acidulated  by  sulphuric 
acid,  beautiful  crystals  are  formed  of  sulphate  of  iodo-strychnine, 
which  polarize  the  light,  as  has  been  discovered  by  Mr.  Herapath. 
The  precipitate  formed  by  iodide  of  mercury  and  potassium,  by 
tannic  acid,  and  by  solution  of  chlorine  in  water,  are  white. 
This  last  reagent  must  be  used  in  relative  large  quantity,  and  the 
precipitate  formed  by  it  does  not  appear  immediately. 
The  precipitates  formed  by  sulphocyanide  of  potassium  and 
neutral  chromate  of  potash  are  both  crystalline.  The  color  of 
the  former  is  white,  and  the  form  of  the  crystals  observed  by  the 
