244    METHODS  FOR  DISCRIMINATING  CINCHONA  ALKALOIDS. 
only  mask  its  appearance  by  their  own  color,  whilst  some  destroy 
it  by  neutralizing  the  excess  of  acid  ;  others  do  so  by  producing 
salts  which  are  themselves  non-fluorescent  media.  Whilst  a 
third  class  destroy  it  by  really  modifying  the  alkaloid  itself. 
IV.  That  as  so  many  reagents  of  common  occurrence  inter- 
fere with  the  manifestation  of  fluorescence,  and  as  it  is  also  a 
property  common  to  all  the  cinchona  alkaloids  herein  described, 
its  appearance  becomes  no  longer  of  any  value  as  a  test  for 
quinine. 
V.  Brandes's  chlorine  and  ammonia  test  will  discover  1  grain 
of  either  quinine  or  quinidin  in  1  gallon  of  water,  but  shows  no 
difference  between  these  alkaloids,  except  in  very  concentrated 
solutions,  when  there  is  a  precipitate  with  quinidin,  but  not  with 
quinine. 
Quinicine  is  also  influenced  by  this  test,  but  less  extensively. 
VI.  Dr.  Vogel's  first  modification  of  this  test  is  of  no  appa- 
rent value  ;  but  by  also  employing  ammonia,  the  author  has 
found  that  it  will  indicate  both  quinine  and  quinidin,  detecting 
readily  1  grain  of  either  in  a  pint,  and  showing  slight  evidence 
with  1  grain  in  10,000  grains  of  water. 
There  is  scarcely  any  reaction  with  quinicine. 
VII.  Dr.  Vogel's  other  modifications  of  Brandes's  test  are 
unimportant,  with  the  exception  of  the  fourth,  viz.,  excess  of 
chlorine,  and  very  little  ammonia.  This  detects  1  grain  in 
about  2000  grains  of  fluid  very  readily,  if  excess  of  acid  be 
avoided  at  first.  The  test,  however,  is  equally  indicative  of 
quinidin ;  it  gives  scarcely  any  perceptible  reaction  with  quini- 
cine. 
VIII.  Pelletier's  chlorine  gas-test  succeeds  very  well  with 
the  free  alkaloids,  but  does  not  show  any  indication  with  their 
salts.  It  is  equally  capable  of  detecting  quinidin,  and  gives  the 
same  phenomena. 
IX.  Marchand's  test  is  not  a  delicate  reaction. 
X.  All  the  foregoing  tests,  although  specially  proposed  for 
the  discovery  of  quinine,  possess  equal  powers,  and  show  the 
same  appearances  with  quinidin.  But  they  have  no  reaction  on 
cinchonine,  cinchonidin,  or  cinchonicine. 
XI.  Van  Heijningen's  test  by  oxalate  of  ammonia,  produces, 
after  some  hours,  a  crystalline  oxalate  of  quinine,  when  using  a 
