METHODS  FOR  DISCRIMINATING  CINCHONA  ALKALOIDS.  243 
When  diluted  with  from  three  to  ten  gallons  of  water,  theSe 
alkaloids  continue  to  exhibit  internal  dispersion. 
Solutions  of  quinicine  are  only  slightly  epipolic,  and  if  the 
change  has  been  perfect,  scarcely  at  all  fluorescent,  but  neverthe- 
less strongly  absorptive  of  rays  of  high  refrangibility. 
Cinchonidin  also  exhibits  optical  phenomena,  but  in  a  much 
slighter  degree,  about  ^th  part  of  that  of  either  quinine  or  qui- 
nidin. 
Cinchonine  is  also  fluorescent  about  ^th  part  of  the  same 
alkaloids. 
II.  That  on  mixing  fluorescent  solutions  of  quinine,  quinidin, 
or  other  cinchona  alkaloid  with  the  soluble  chlorides,  although 
all  traces  of  optical  phenomena  are  lost  to  the  eye,  yet  the 
media  still  possesses  powerfully  absorbent  powers  on  the  rays  of 
high  refrangibility,  and,  if  sufficiently  concentrated,  are  wholly 
opaque  to  them,  without  exhibting  any  of  the  phenomena  of  dis- 
persion, and  greatly  impede  chemical  action. 
This  was  proved  by  three  methods  of  observation  : — 
1st.  By  introducing  vessels  containing  fluorescent  solutions 
of  quinine  into  other  vessels  filled  with  non-fluorescent  solutions 
of  the  alkaloids,  produced  by  previous  admixture  with  chloride 
of  ammonium,  when  all  optical  phenomena  disappeared  from  the 
inner  vessel. 
2ndly.  By  surrounding  fluorescent  specimens  of  fluor-spar  with 
these  prepared  solutions  of  the  alkaloids,  when  the  blue  color  in 
the  spar  immediately  disappeared. 
3rdly.  By  photography ;  employing  concentrated  solutions  of 
quinine  mixed  with  chloride  of  ammonium  in  troughs  to  inter- 
cept the  incident  light  from  any  object  anterior  to  the  camera, 
when  it  was  found  almost  impossible  to  obtain  any  image  upon 
the  sensitive  collodion  plate,  although  the  intensity  of  the  visi- 
ble image  received  on  the  ground-glass  screen  did  not  suffer  any 
apparent  diminution. 
4thly.  By  photographic  printing;  troughs  containing  these 
solutions  obstructed  the  chemical  rays  very  considerably,  thus 
interfering  with  the  production  of  a  positive  picture  from  the 
negative,  much  longer  exposure  being  necessary  to  produce  any 
chemical  effect. 
III.  That  certain  reagents  do  not  destroy  fluorescence  ;  others 
