20  The  Color  of  Fluorescent  Solutions.     { k™^°Xnn™' 
If  one  of  the  little  Geissler  tubes  containing  nitrogen,  called  u  spec- 
trum tubes,"  be  jacketed  by  means  of  a  perforated  cork  and  a  large 
glass  tube,  and  the  jacket  filled  with  pure  or  non-fluorescent  benzine, 
then  illuminating  the  tube,  and  with  a  pipette  dropping  in  that  petro- 
leum product,  called  "  cosmoline"  (a  lubricating  oil  made  by  E.  H. 
Houghton,  of  Philadelphia),  each  drop  will  appear  of  a  rich  blue  as  it 
dissolves  in  the  benzine,  which  soon  acquires  a  magnificent  blue  fluo- 
rescence. Increasing,  however,  the  quantity  of  cosmoline  oil  until 
its  color  begins  to  take  effect,  the  tint  of  the  fluorescence  gradually 
changes  to  a  rich  green. 
By  a  little  care  a  blue  solution  may  be  superposed  on  a  green  one 
in  the  same  tube. 
Another  semi-solid  preparation  of  cosmoline,  which  has  a  very  light 
color,  gives  a  solution  with  benzine  fluorescing  of  a  magnificent  blue. 
I  have  this  substance  now  under  investigation,  and  hope  soon  to  be 
able  to  make  some  further  observations  upon  it.* 
Returning  to  the  solutions  of  turmeric  I  have  found  that  the  fluo- 
rescent body  in  that  substance  is  not  its  essential  oil  nor  its  brown 
coloring  matter,  but  either  the  yellow  coloring  matter  itself,  or  some- 
thing so  closely  allied  to  it  in  solubility  that  I  have  thus  far  been  un- 
able to  effect  any  separation. 
In  connection  with  this  let  me  say  that  I  am  much  indebted  to  Mr. 
Robt.  F.  Fairthorne,  of  Philadelphia,  who  has  aided  me  greatly  in  the 
preparation  of  the  various  constituents  of  turmeric  in  a  state  of  purity. 
In  my  former  paper  I  mentioned  that  uranium  nitrate  in  solution 
gave  a  very  faint  fluorescence. 
This  appearance  I  now  find  was  due  entirely  to  the  above-explained 
action  of  the  tube,  and  a  number  of  carefully  conducted  observations 
now  convince  me  that  this  substance,  while  it  fluoresces  so  vividly  in 
the  solid  state,  loses  that  property  entirely  when  in  solution. 
I  have  also  found  that  a  saturated  solution  of  acid  quinine  sulphate 
has  its  fluorescence  much  increased  by  dilution. 
Lastly,  let  me  remark  that  I  by  no  means  assert  that  all  solutions 
fluoresce  blue,  but  simply  those  which  I  have  examined.  There  are 
many  which  I  have  as  yet  been  unable  to  procure  or  study,  whose  re- 
lations in  this  respect  I  hope  soon  to  investigate. — Amer.  Journ.  Set 
and  Arts,  Nov.,  1871. 
*  Mr.  Houghton  tells  me  that  "  cosmoline"  is  prepared  from  crude  petroleum 
by  evaporation  in  vacuo  and  nitration  through  animal  charcoal  only,  without 
any  chemical  treatment. 
