26 
TESTING  FOR  QUININE  AND  QUINIDIN. 
right  angles  to  the  polarizing  plate;  whilst  those  at  90°  to  these 
educe  the  complimentary  tint,  as  the  analyzing  plate  would  also 
have  done  if  revolved  through  an  arc  of  90°.  Vide  figs.  1  and  2. 
This  test  is  so  ready  of  FlG- 2—Blue  Stage- 
application  and  so  delicate 
that  it  must  become  the 
test,  par  excellence,  for 
quinine.  Vide  figs.  1  and 
2. 
Not  only  do  these  pecu- 
liar crystals  act  in  the  way 
just  related,  but  they  may 
be  easily  proved  to  possess 
the  whole  of  the  optical 
properties  of  that  remark- 
able salt  of  quinine,  so 
fully  described  by  me  in 
the  PharmacuetiealJour- 
nal,  vol.  xi.,  pages  448 
and  499,  and  the  chemical 
analysis  of  which  was  pub- 
lished in  vol.  xii.  of  the 
same  Journal ;  in  fact, 
these  crystals  are  perfect- 
ly identical  with  the  sul- 
phate of  iodo-quinine  in 
every  respect. 
To  test  for  quinidine,  it  is 
merely  necessary  to  allow 
the  drop  of  acid  solution 
to  evaporate  to  dryness 
upon  the  slide,  and  to  ex- 
amine the  crystalline  mass 
bytwotourmalines,crossed  Water, 
at  right  angels  and  without  the  stage.    Immediately  little  circu- 
lar discs  of  white,  with  a  well  defined  black  cross  very  vividly 
shown,  start  into  existence,  should  quinidine  be  present  even  in 
very  minute  traces.    Vide  fig.  3. 
This  is  generally  the  case  if  hospital  quinine  or  that  of  the 
