6       CHEMICAL  COMPOSITION  OF  GELSEMIUM  SEMPERVIRENS. 
beautiful  deep  blue  coloration  will  manifest  itself  along  the  path 
of  the  drop  as  it  slowly  diffuses  itself  through  the  water,  es- 
pecially if  the  diffusion  be  observed  under  a  cone  of  condensed 
sun-light.  A  single  drop  of  a  10,000th  solution  of  the  acid, 
when  examined  in  this  manner,  yields  an  intense  blue  coloration 
along  the  path  of  the  alkaline  liquid.  Even  a  drop  of  a 
100,000th  solution  gives  rise  to  a  very  satisfactory  blue  colora- 
tion. 
The  commercial  fluid  extract  of  gelsemium,  when  rendered 
alkaline  and  diluted  with  water,  presents  appearances,  in  regard 
to  color,  similar  to  those  above  described,  even  if  the  extract  be 
largely  diluted.  Thus,  if  the  extract  be  rendered  alkaline,  and 
diluted  with  one  hundred  parts  of  water,  the  mixture  presents  a 
strongly  marked  blue  appearance  when  examined  by  looking 
into  the  tube  containing  the  mixture.  Even  when  diluted  with 
one  thousand  parts  of  water,  it  still  presents,  under  condensed 
light,  a  very  distinct  blue  coloration,  even  if  only  a  few  drops 
of  the  mixture  be  examined. 
In  respect  to  the  manifestation  of  a  blue  appearance  under 
the  action  of  light,  solutions  of  gelseminic  acid  resemble  some- 
what those  of  quinine,  with,  however,  this  marked  difference, 
that  in  the  case  of  the  latter  substance  the  coloration  is  only 
observed  when  the  solution  has  an  acid  reaction,  whereas  in  the 
case  of  gelseminic  acid  the  coloration  manifests  itself  only  in  the 
presence  of  an  alkali,  the  bluish  appearance  immediately  dis- 
appearing on  the  addition  of  an  excess  of  an  acid. 
When  cautiously  heated  upon  platinum  foil,  pure  gelseminic 
acid  fuses  to  a  colorless  liquid,  which,  as  the  heat  is  increased, 
darkens  in  color,  gives  off  white  fumes  and  is  finally  dissipated 
without  residue. 
If  a  small  quantity  of  the  crystallized  acid  be  placed  within  a 
glass  ring  which  is  attached  to  a  glass  slide,  and  the  latter  be 
gradually  heated  on  an  iron  plate  placed  over  a  Bunsen  burner, 
the  acid  undergoes  no  change  until  heated  considerably  above 
212°  F.,  when  it  volatilizes  without  fusion  or  change  of  color. 
If  the  vapors  thus  produced  be  received  upon  a  warmed  glass 
slide  or  cover  placed  upon  the  glass  ring,  they  condense  in  the 
form  of  brilliant,  transparent  crystals  of  one  or  more  of  the 
