57°  On  Some  of  the  Tests  for  Quinine.  {Ag^&^jS?' 
yellow,  of  the  alcoholic  solution  of  iodine  is  then  added.  Very 
soon  portions  of  the  mixture  will  present  a  dark  green  deposit, 
which  when  examined  by  a  moderate  power  (75  diam.)  of  the 
microscope  will  be  found  to  consist  of  the  crystals  in  question.  The 
formation  of  these  crystals  is  perfectly  characteristic  of  quinine. 
The  residue  from  one  drop  of  a  i-iooth  solution  of  quinine,  in 
the  form  of  sulphate,  when  treated  with  a  drop  of  the  acetic  acid 
mixture  and  then  sufficient  of  the  iodine  solution  to  impart  a  strong 
color,  will  yield  innumerable  crystals  of  the  iodosulphate  compound* 
A  1.500th  solution  residue  will  generally  yield  an  abundant 
deposit  of  the  crystals. 
The  residue  from  a  drop  of  a  i-ioooth  solution,  if  simply  mois- 
tened with  the  acetic  acid  liquid  and  then  with  a  minute  drop  of 
the  iodine  solution,  may  yield  satisfactory  results ;  but  it  requires  a 
nice  adjustment  of  the  reagents  to  obtain  satisfactory  results  from 
this  quantity  of  the  alkaloid. 
3.  FLUORESCENCE. 
One  of  the  most  striking  properties  and  at  the  same  time  the 
most  delicate  reaction  of  quinine  at  present  known,  is  the 
fluorescence  of  solutions  of  its  oxysalts,  especially  the  sulphate. 
Normal  solutions  of  the  hydrochloride,  hydrobromide,  hydriodide 
and  hydrocyanide  present  little  or  no  fluorescence.  A  solution  of 
the  hydrochloride  containing  a  limited  excess  of  hydrochloric  acid, 
may,  as  pointed  out  by  Prof.  R.  A.  Witthaus,1  present,  a  well 
marked  or  even  strong  fluorescence,  especially  in  dilute  solutions ; 
but  this  is  permanently  destroyed  by  a  slightly  larger  quantity  of 
the  free  acid. 
When  in  solution  as  quinine  normal  acid  sulphate,  without  excess 
of  acid,  and  examined  by  ordinary  reflected  light  in  volumes  of  50 
to  100  c.c.  the  blue  fluorescence  is  very  intense  in  the  i-iooth, 
1-iOOOth,  and  i-iOOOOth  solutions,  and  very  well  marked  in  a 
i-5OO0Oth  solution;  but  it  is  not  apparent  in  a  1-iOOOOOth  solution, 
and  is  only  faintly  marked  even  under  a  cone  of  condensed  sunlight. 
If  1  c.c.  of  the  acid  sulphate  solution,  placed  in  a  small  test  tube, 
be  examined  it  will  present  as  follows : 
(1)  i-iooth  solution,  a  very  strong  blue  fluorescence  in  reflected 
light,  which  becomes  intense  in  condensed  sunlight. 
1  Researches  Loomis  Laboratory,  1892,  91. 
