460 
CHEMICAL  TESTS  FOR  STRYCHNIA. 
of  a  lesser  specific  gravity  than  1-840.  An  acid  whose  density 
is  1-500  is  still  better. 
The  substances  hitherto  employed  are  binoxide  of  lead,  binox- 
ide  of  manganese,  chlorate  of  potash,  and  bichromate  of  potash. 
According  to  my  experiments  the  chlorate  of  potash  is  the  least 
valuable,  much  better  the  binoxide  of  lead,  better  still  binoxide 
of  manganese,  and  best  of  all,  bichromate  of  potash. 
The  first  thing  to  be  done  is  the  preparation  of  a  solution  of 
strychnia  of  determinate  strength — one  grain  in  500  minims  is  a 
convenient  proportion.  The  solution  is  readily  effected  by  using 
equal  proportions  of  rectified  spirit  and  distilled  water  acidulated 
with  sulphuric  acid. 
Place  one  minim  of  this  solution  upon  a  clean  white  porcelain 
capsule,  and  evaporate  at  a  gentle  heat  to  dryness,  now  add  a 
drop  of  sulphuric  acid,  and  intimately  mix  ;  introduce  a  small 
fragment  of  bichromate  of  potash,  and  draw  it  across  the  spot. 
Where  the  quantity  of  strychnia  is  as  great  as  in  this  experiment 
i.  e.  the  l-500th  of  a  grain,  a  saturated  solution  of  the  bichromate 
may  be  used,  and  is,  in  some  respects,  better,  but  it  is  necessary 
to  use  it  judiciously ;  a  pointed  glass  rod  is  dipped  into  the  so- 
lution, and  enough  allowed  to  remain  upon  it  without  dropping ; 
wherever  the  point  of  this  touches  the  mixture,  the  color  is  de- 
veloped. This  color  is  blue,  which  is  succeeded  by  purple,  crim- 
son, red,  and  green,  the  latter  in  some  instances  being  eventually 
replaced  by  yellow.  (These  colors  are  well  seen  if  a  small  frag- 
ment of  strychnia  be  placed  in  a  narrow  test  tube,  and  a  suf- 
ficient quantity  of  sulphuric  acid  added  to  smear  the  inner  sur- 
face on  inclining  and  turning  the  tube  about.  A  little  pounded 
bichromate  of  potash  being  introduced,  and  the  tube  held  so  as 
to  trail  the  acid  over  it,  the  most  magnificent  colors  are  brought 
out.)  A  given  quantity  of  the  solution  is  now  mixed  with  an 
equal  proportion  of  distilled  water,  each  minim  then  containing 
a  thousandth  part  of  a  grain ;  from  the  solution  thus  formed,  it 
is  easy  to  obtain  others  of  any  degree  of  dilution  that  may  be 
desired.  This  dilution  may  be  carried  to  such  an  extent,  that 
the  l-500,000th  part  of  a  grain  may  be  faintly  detected,  be- 
yond which  I  have  not  succeeded.  The  method  by  which  this 
latter  quantity  was  shown,  is  as  follows:  prepare  a  solution  of 
such  a  strength  that  one  minim  shall  exactly  equal  the  1-125, 000th 
