518 
COLOR  TESTS  FOR  STRYCHNIA,  ETC. 
Hence  the  acid  itself  becomes  a  test  of  no  mean  value.  It  serves, 
as  I  shall  point  out  more  particularly  presently,  to  distinguish 
strychnia  from  a  considerable  number  of  the  alkaloids,  and  also 
from  several  substances  which  give  with  sulphuric  acid  alone 
colored  reactions,  some  of  which  reactions  with  the  acid  alone 
bear  a  certain  resemblance  to  those  of  strychnia  with  sulphuric 
acid  plus  the  bichromate  of  potash,  ferricyanide  of  potassium, 
permanganate  of  potash,  peroxide  of  lead,  or  peroxide  of  man- 
ganese. In  order  to  distinguish  strychnia  from  other  alkaloids, 
and  from  the  substances  to  which  I  have  just  referred,  it  is  es- 
sential that  the  sulphuric  acid  should  be  first  applied  to,  and 
well  mixed  with,  the  strychnia,  and  that  the  absence  of  color 
having  been  noted,  the  reagents  that  develop  the  color  should 
be  in  their  turn  applied.  In  all  that  I  have  said  on  the  subject 
of  the  color-tests  for  strychnia,  and  in  what  I  have  yet  to  say, 
I  assume  this  mode  of  procedure  to  be  strictly  observed;  and  I 
shall  continue  to  speak  of  these  reagents  as  the  color-producing 
tests. 
I  have  hitherto  assumed  that  the  sulphuric  acid  is  applied 
cold  ;  but  I  shall  presently  point  out  that  we  may  greatly  add 
to  the  value  of  this  constituent  portion  of  the  color  tests  by  first 
warming  and  then  heating  the  acid  solution.  A  very  slight  rise 
of  temperature  serves  to  develop  very  beautiful  and  characteris- 
tic colors  in  some  of  the  alkaloids,  while  it  does  not  change  the 
color  of  strychnia.  A  further  rise  of  temperature  to  the  point 
of  causing  the  mixture  to  give  ofi"  vapor,  develops  color  in  strych- 
nia also,  and  deepens  or  changes  the  tints  already  imparted  to 
the  alkaloids  previously  affected  by  warming  the  acid  mixture. 
The  color  imparted  to  a  solution  of  strychnia  in  sulphuric 
acid  by  raising  it  to  a  temperature  at  which  it  gives  off  vapor 
is  not  strongly  marked.  It  is  a  faint  yellow  or  light  greenish- 
brown,  differing  somewhat  in  depth  of  tint  with  different  speci- 
mens of  strychnia  treated  in  all  respects  exactly  alike.  If  the 
acid  solution  is  allowed  to  cool,  it  no  longer  acts  characteris- 
tically with  the  bichromate  of  potash  or  the  other  tests.  Their 
action  is  wholly  destroyed  or  greatly  impaired.  Hence,  in  ap- 
plying the  color-tests  for  strychnia  we  must  use  concentrated 
pure  sulphuric  acid,  and  use  it  cold. 
So  much  for  the  first  part  of  the  color-tests.    We  add  to  the 
