4  64  Color  of  Fluorescent  Solutions.      { ^.^i^""- 
simply  due  to  the  absorptive  action  of  the  colored  solution,  and  not 
to  the  development  of  green  rays.  Examined  with  the  spectroscope, 
the  seemingly  green  fluorescence  showed  no  increase  in  the  green  or 
yellow  part  of  the  spectrum,  as  compared  with  the  blue  fluorescence, 
but  only  an  absorption  of  the  red  and  violet  ends.  When,  however,, 
a  piece  of  fluorescing  canary  glass  or  solid  nitrate  of  uranium  was- 
examined,  the  green  light  was  (as  is  well  known)  largely  augmented. 
I  also  found  that  when,  by  filtration  through  animal  charcoal,  the 
solution  in  turpentine  was  reduced  in  color,  the  green  tint  of  the  fluo- 
rescence disappeared  in  a  corresponding  degree.  This  alone  would^ 
however,  have  proved  nothing,  as  a  green  fluorescing  matter  might 
have  been  absorbed  by  the  charcoal,  but  in  connection  with  the  spec- 
troscopic result  it  was  of  interest. 
I  next  took  up  for  examination  the  tincture  of  turmeric.  This  is 
set  down  in  standard  works,  such  as  those  of  Du  Moncel  and  Becque-^ 
rel,  as  fluorescing  red.  This  solution,  when  concentrated,  has  a  rich 
orange-red  color,  and  the  jacket  of  a  Geissler  tube  being  filled  with 
it,  all  the  light  reaching  the  eye,  from  the  electric  discharge  within, 
is  of  a  deep  orange  or  red  color.  If,  however,  the  solution  is  simply 
diluted  until  its  color  is  reduced  to  a  rich  yellow,  the  fluorescence  ap- 
pears green.  The  same  result  follows  from  filtration  through  bone 
black,  with  a  marked  increase  in  the  amount  of  fluorescence  visible,, 
as  the  light-absorbing  coloring  matter  is  removed.  By  continuing  the 
decoloration  until  the  liquid  is  colorless  or  of  a  very  light  tint,  its  fluo- 
rescence is  distinctly  blue. 
The  results  with  the  spectroscope  when  it  v.'as  applied  to  this  sub- 
stance, were  the  same  as  with  the  solution  of  asphalt.  Such  also  is 
the  case  with  tinctures  of  chlorophyl,  which,  when  fresh  and  green,, 
gives  apparently  a  green  light,  and,  when  old  and  brown,  a  gray 
color. 
Finally,  I  took  up  the  nitrate  of  uranium,  about  which  such  con-^ 
tradictory  statements  have  been  published.  This  salt  in  its-  solid' 
state  gives  a  brilliant  green  fluorescence,  whose  spectrum  is  figured  by 
Becquerel,  and  abounds  in  green  rays  ;  but  in  solution  it  gives  a  very 
feeble  fluorescence,  far  inferior  to  that  of  turmeric,  and  of  no  more 
green  tint  than  would  be  due  to  its  yellow  color.  So  in  fact  says 
also  the  spectroscope. 
From  these  results  it  would  seem  that  the  molecules  of  fluorescent 
bodies  m  solution  are  not  capable  of  restricting  their  vibrations  to- 
