NEWLY-DISUOVERED  SALT  OF  QUININE.  137 
which  crystalline  substance  possesses  the  power  of  polarizing 
a  ray  of  light  like  tourmaline,  and,  at  certain  angles  of  rotation, 
of  depolarizing  it,  like  selenite.  By  dissolving  the  disulphates 
of  quinine  and  cinchonine  of  commerce  in  concentrated  acetic 
acid,  upon  warming  the  solution,  and  dropping  into  it  a  spiritu- 
ous solution  of  iodine  carefully  by  small  quantities  at  a  time, 
and  placing  the  mixture  aside  for  some  hours,  large  brilliant 
plates  of  this  substance  were  produced.  Iodine,  sulphuric  acid, 
and  quinine,  are  the  constituent  elements  of  this  substance. 
Dr.  Herapath  considers  it  probable  that  these  are  arranged  as 
a  binary  compound ;  the  disulphate  of  quinine  acting  as  a  feeble 
electro-positive  base,  to  the  iodine  as  an  electro-negative.  He 
considers  it,  therefore,  to  be  an  iodide  of  the  disulphate  of 
quinine.  The  crystals  of  this  salt,  when  examined  by  reflected 
light,  have  a  brilliant  emerald-green  color,  with  almost  a  metallic 
lustre;  they  appear  like  portions  of  the  elytra  of  cantharides, 
and  are  also  very  similar  to  murexide  in  appearance.  When 
examined  by  transmitted  light,  they  scarcely  possess  any  color, 
there  is  only  a  slightly  olive-green  tinge ;  but  if  two  crystals 
crossing  at  right  angles  be  examined,  the  spot  where  they  intersect 
appears  as  black  as  midnight,  even  if  the  crystals  are  not  JL  of 
an  inch  in  thickness.  If  the  light  used  in  this  experiment  be 
in  the  slightest  degree  polarized,  as  by  reflection  from  a  cloud, 
or  by  the  blue  sky,  or  from  the  glass  surface  of  the  mirror  of 
the  microscope  placed  at  the  polarizing  angle,  56°  45',  these 
little  prisms  immediately  assume  complementary  colors.  One 
appears  green  and  the  other  pink;  and  the  part  at  which  they  cross 
is  a  deep  chocolate  or  chestnut  brown,  instead  of  black.  In  per- 
forming optical  experiments  with  this  peculiar  salt,  Dr.  Herapath 
says,  that  it  is  not  necessary  to  employ  a  ^tourmaline  ;  the 
whole  phenomena  may  be  exhibited  with  equal  brilliancy 
by  using  two  plates  of  iodide  of  the  disulphate  of  quinine  ; 
one  as  a  polarizer,  the  other  as  an  analyzer,  the  selenite 
-and  disulphate  of  quinine  being  interposed.  This  fully  es- 
tablishes the  fact  of  this  substance  possessing  optical  proper- 
ties precisely  equivalent  to  those  of  a  tourmaline,  or  of  a 
Nicol's  prism,  and  will  be  sufficient  to  show  that  all  the  pheno- 
mena capable  of  being  produced  by  the  one  may  be  exhibited 
by  the  other.    Dr.  Herapath  further  states,  that  this  newly- 
