ON  THE  DETECTION  OF  PICROTOXINE. 
455 
we  can  remove  the  organic  base  by  ether  from  an  aqueous  so- 
lution, while  the  same  course  pursued  with  picrotoxine  would 
fail  to  remove  any  of  it  from  the  water,  it  being  positively  ne- 
cessary that  the  solution  should  be  neutral  or  acid  to  enable  the 
ether  to  dissolve  it. 
Picrotoxine  is  soluble  in  one  hundred  and  fifty  parts  of  cold 
water,  but  if  a  small  quantity  of  caustic  alkali  is  present  it  will 
readily  dissolve  in  six  or  eight  times  its  volume.  When  this 
solution  is  gently  heated  it  becomes  yellow,  and  on  platinum 
at  a  temperature  far  below  ignition  assumes  a  brick-red  color 
which  is  distinctive  and  quite  unlike  the  shade  produced  by 
sugar  under  similar  circumstances.  Picrotoxine,  like  sugar  and 
many  indifferent  organic  bodies,  possesses  the  property  of  re- 
ducing certain  metallic  oxyds.  "  It  changes  bichromate  of 
potass  to  a  fine  green  color."  (Gmelin.)  "An  alkaline  solution, 
of  picrotoxine  reduces  sulphate  of  copper  to  the  suboxyd." 
(Otto.)  This  property,  however,  is  common  to  too  many  other 
substances  to  be  at  all  distinctive.  A  far  more  reliable  test  is 
found  in  oxydation. 
If  dry  picrotoxine  and  nitrate  of  potassa  are  rubbed  together 
in  a  watch-glass,  and  a  drop  of  sulphuric  acid  is  added,  no  per- 
ceptible change  occurs  ;  but  if  a  strong  solution  of  caustic  soda 
or  potassa  is  poured  upon  this,  a  bright  reddish-yellow  color  is 
communicated  to  the  mixture  which  partially  dissolves  and 
causes  the  whole  liquid  to  assume  the  same  tint.  In  this  way 
very  minute  traces  of  picrotoxine  may  be  discovered,  so  small  a 
quantity  as  _JL  of  a  gramme,  if  pure,  being  detected  with  the 
greatest  ease.  When  as  small  a  quantity  as  this  is  used  we  see 
the  color  most  distinctly  by  gently  breaking  the  solid  cake  of 
sulphate  of  potassa  which  lies  on  the  bottom  of  the  dish  ;  por- 
tions of  the  precipitate  will  then  appear  of  a  crimson  or  purple 
hue. 
In  applying  this  test  it  is  best  to  add  about  three  or  four 
times  the  quantity  of  nitrate  of  potash  that  we  have  of  sub- 
stance to  be  examined,  and  to  use  no  more  sulphuric  acid  than 
is  necessary  to  moisten  the  mass.  The  solution  of  potassa  or 
soda  should  be  made  very  strong,  and  enough  added  to  ensure 
considerable  alkalinity  in  the  mixture  after  the  neutralization  of 
the  sulphuric  acid. 
