250        IODO-SULPHATES  OF  THE  CINCHONA  ALKALOIDS. 
when  a  large  quantity  of  cinchonine  exists,  this  compound  will 
also  appear  along  with  the  quinidin  salt. 
This  test  is  a  beautiful  and  ready  method  of  proving  the 
presence  of  cinchonidin  in  cinchonine,  which  would  otherwise 
be  considered  pure,  Brandes'  test  having  shown  the  abseuce  of 
quinine  and  quinidin.  In  the  same  way,  this  test  is  an  easy 
method  of  detecting  mixtures  of  quinine  and  quinidin,  the  opti- 
cal characters  of  the  two  salts  being  so  well  marked,  that  no 
difficulties  can  exist  in  their  discrimination. 
It  does  not  offer  such  facilities  for  the  separation  of  quinine 
from  cinchonidin  ;  the  two  salts  go  down  together,  especially 
if  large  quantities  of  cinchonidin  exist  with  mere  traces  of 
quinine. 
For  the  success  of  this  test,  a  small  portion  only  is  necessary ; 
with  quinine  and  quinidin  J_th  part  of  a  grain  has  furnished 
evidence  of  the  two  alkaloids  ;  one  grain  would  be  abundant  to 
detect  all  the  alkaloids. 
The  foregoing  method  of  examination  has  enabled  the  author 
to  prove  that  the  substance  which  Rosengarten,  of  Philadelphia, 
called  quinidin,  was  really  the  cinchonidin  of  Pasteur,  and  the 
details  of  his  cures  for  fever,  therefore,  by  quinidin,  are  rather 
to  be  ascribed  to  cinchonidin. 
The  cinchonidin  of  Wittstein,  of  Munich,  is  a  totally  different 
alkaloid,  giving,  with  sulphuric  acid  and  iodine,  a  salt  at  once  to 
be  distinguished  by  the  eye  from  either  of  the  two  iodo-sulphates 
described,  but  yet  possessing  optically  doubly  absorbent  powers. 
This  salt  has  a  deep  orange-yellow  color  by  transmitted  light, 
merging  into  sienna-brown  in  thicker  plates,  which  are  generally 
flat  and  much  imbricated  in  the  method  of  crystallization,  and 
also  derived  from  a  rhombic  prism.  The  reflected  tints  are 
brownish-olive,  not  unlike  dead  leaves,  or  brown  beech-leaves. 
These  crystals  are  more  doubly  absorbent  than  either  the 
quinidin  or  cinchonine  salt,  but  less  powerfully  optical  as  tour- 
malines than  the  quinine  or  cinchonidin  compounds.  When 
polarized,  they  transmit  a  sienna-brown  body-color  if  moderate- 
ly thick,  and  thicker  plates  are  bistre-brown,  but  when  suffi- 
ciently thick,  they  are  wholly  impervious  to  plane-polarized 
light.  The  substance  was  not  in  sufficient  quantity  to  admit  of 
any  analysis. 
