ON  TODO-SULPHATE  OF  QUININE.  23 
if  the  tourmalines  are  rotated  45°,  so  as  to  place  the  crystals 
at  the  depolarizing  angle  both  crystals  become  colored,  a  being 
green  and  b  pink,  as  in  fig.  9.  If  8  hexagonal  tables  are  placed 
with  their  axes  on  the  radii  of  a  circle  45°  apart,  every  alternate 
crystal  will  be  black  and  the  intermediate  ones  colored  pink 
and  green. 
Other  and  different  colors  are  developed  when  only  the  infe- 
rior tourmaline  is  employed  with  a  selenite  plate  superimposed. 
Dr.  Herapath  concludes  his  second  essay  with  directions  for 
mounting  crystals  of  iodo-sulphate  of  quinia  so  as  to  use  them 
in  lieu  of  tourmalines  in  polarizing  apparatus,  to  which  he  con- 
siders them  not  only  equal,  but  as  possessing  the  power  of  polar- 
ization with  five  times  the  intensity  that  thd  best  tourmalines  are 
capable  of. 
When  disulphate  of  quinidin  is  dissolved  in  acetic  acid,  and  a 
drop  placed  on  a  glass  is  allowed  to  evaporate,  it  is  found  to  crys- 
tallize in  tufts  of  radiating  prisms,  some- 
times arranged  in  a  perfect  circle.  When 
such  a  tuft  is  placed  on  a  tourmaline  sur- 
mounted by  the  red  selenite  stage,  two  op- 
posite quadrants  of  the  circle  in  fig.  10, 
between  315°  and  45°,  and  between  225° 
and  135°,  appear  decidedly  pink,  whilst 
the  other  two  between  45°  and  135°  and 
between  315°  and  225°  are  green  and 
greenish  yellow.  This  appearance  is  so  striking  as  to  character- 
ize quinidin. 
We  are  now  prepared  to  understand  our  author's  remarks  in 
his  last  paper,  (Pharm.  Journal,  xiii.  216,)  "  On  the  discovery  of 
quinine  and  quinidine  in  the  urine  of  patients  under  medical 
treatment,  with  the  salts  of  those  mixed  alkaloids."  After  allu- 
ding to  the  interest  manifested  by  professional  men  in  tracing 
or  endeavoring  to  trace  the  course  of  remedies  ingested,  and  the 
importance  of  this  kind  of  knowledge  in  properly  understanding 
the  modus  operandi  of  medicines,  he  observes  that  one  drawback 
to  the  progress  of  inquiry  in  this  direction  has  been  the  difficulty 
of  recognizing  the  organic  principles  of  medicinal  agents  in  the 
animal  fluids  with  such  certainty  as  to  render  their  presence  un- 
doubted. 
Having  been  struck  with  the  facility  of  application,  and  tha 
extreme  delicacy  of  the  reaction  of  polarized  light,  when  experi* 
Fig  10. 
