CHEMICAL  COMPOSITION  OF  GELSEMIUM  SEMPERVIRENS.  5 
solves  it,  in  the  form  of  a  salt,  to  a  solution  having  very  striking 
fluorescent  properties,  even  when  very  highly  diluted.  A  solu- 
tion of  this  kind  containing  of  its  weight  of  the  acid,  when 
examined  in  a  small  glass  tube  by  transmitted  light,  has  a 
strong  yellow  color ;  under  reflected  light,  a  deep  bluish  appear- 
ance ;  and  under  a  cone  of  sun-light  condensed  upon  it  -with  an 
ordinary  hand  lens,  an  intense  blue  color  along  the  path  of  the 
condensed  rays. 
When  the  solution  contains  j^^^^^  weight  of  the  acid, 
it  presents,  under  transmitted  light,  a  greenish-yellow  appear- 
ance, the  surface  of  the  liquid  at  the  same  time  appearing  of  a 
deep  blue  color  ;  by  reflected  light,  it  presents  a  strong  greenish- 
blue,  and  under  condensed  light,  a  deep  blue  coloration. 
A  10,000th  solution  of  the  acid  presents,  under  transmitted 
light,  only  a  faint  yellowish  hue,  with  a  blue  surface  ;  but  under 
reflected  light  it  appears  of  a  deep  blue  color,  even  more  intense 
than  a  1000th  solution. 
A  100,000th  solution  is  colorless,  or  at  most  presents  only  a 
faint  bluish  hue  under  transmitted  light ;  under  reflected  sun- 
light, however,  it  presents  a  strongly  marked  blue  appearance  ; 
and  when  examined  by  condensed  sun-light,  the  path  of  the  con- 
densed beam,  as  it  passes  through  the  solution,  presents  a  deep 
blue  appearance.  This  blue  coloration  is  also  observed  by  look- 
ing down  the  tube  containing  the  solution  upon  the  surface  of  the 
liquid.  Even  one  grain  of  such  a  solution,  when  contained  in 
the  end  of  a  pipette  and  examined  under  condensed  sun-light, 
exhibits  a  very  distinct  blue  appearance. 
Solutions  more  dilute  than  the  last  mentioned  appear  nearly 
or  altogether  colorless  under  transmitted  and  reflected  light  ; 
but  even  a  single  drop  of  a  solution  containing  only  the 
TOioA, 0  00^^1  part  of  its  weight  of  the  acid,  when  contained  in  the 
end  of  a  pipette  and  examined  under  a  cone  of  condensed  sun- 
light, presents  a  quite  perceptible  blue  coloration  along  the  path 
of  the  condensed  rays. 
If  a  large  test  tube,  or  any  similar  vessel,  nearly  filled  with 
water,  be  placed  against  a  black  ground  in  direct  sun-light,  and 
view  obliquely  from  the  front,  and  then  a  drop  of  an  alkaline 
solution  of  the  organic  acid  be  dropped  into  the  tube,  a  very 
