EDITORIAL.  PEREIRA's  MATERIA  MEDICA. 
181 
Fier.  280. 
of  circular  polarization  to  the  detection  or  determination  of  substances. 
When  ordinary  light  is  reflected  at  a  certain  angle  from  a  glass  mirror  its 
nature  is  changed  and  it  becomes  polarized.  Biot  and  other  physicists  have 
noticed  that  when  such  an  altered  ray  of  light  passes  through  certain  trans- 
parent liquido,  and  a  Nichols  prism,  a  double  image  is  seen,  which  is  either 
to  the  right  or  the  left  of  the  operator.  This  property,  due  to  the  molecular 
structure  of  the  liquids,  is  so  constant  as  to  have  been  used  to  detect  one  in 
the  other,  as,  for  instance  grape  sugar  syrup  in  cane  sugar  syrup.  The  fol- 
lowing quotation  and  engravings,  will  exhibit  the  ex- 
tent to  which  our  author  has  carried  his  illustrations. 
"  Plan  of  apparatus  to  show  the  circular  polarization  of 
oil  of  Turpentine. 
a.  A  ray  of  common  unpolarized  light. 
b.  A  glass  reflector  placed  at  an  angle  56°  45  for  affect- 
ing the  plane  polarization  of  the  light. 
c.  The  reflected  plane- polarized  ray. 
d.  The  oil  of  turpentine  which  effect?  the  double  refrac- 
tion and  rotation  of  the  plane-polai  ized  light. 
e.  The  emergent  circularly-polarized  light. 
/.  The  analyser  (a  double  refracting  rhomb  of  calcareous 
spar)  which  produces  two  colored  images ;  one  caused  by 
ordinary  refraction  and  called  the  ordinary  image,  (o,)  the 
other  by  extraordinary  retraction,  and  termed  the  extraordi- 
nary image  (x.) 
g.  A  lens  employed  to  produce  well  denned  images. 
When  the  eye  is  applied  to  the  aperture  above  or  in 
front  of  the  lens  g,  two  circular  discs  of  colored  light  (fig. 
231)  are  perceived  ;  one  (o)  the  ordinary,  the  other  (x)  the 
Fig.  281. 
extraordinary.  The  colors  of  these 
images  are  complementary  to  each 
other.  By  rotating  the  analyser  (/)  on 
its  axis,  the  extraordinary  image  (x)  re- 
volves around  the  ordinary  image  (o) ; 
each  image  undergoing  a  succession  of 
changes  of  color;  the  se*quence  of  colors 
being  different  for  the  English  [Ameri- 
can] and  French  oils  of  turpentine. 77 
Under  the  head  of  salicin  the  singular  fact  is  stated  that  salicin  in 
its  passage  through  the  system  undergoes  oxidation  and  becomes  hyduret 
of  salicyle  (oil  of  spirea  ulmaria)  in  the  urine,  which  is  rendered  evident 
by  a  per  salt  of  iron  producing  a  purple  color. 
Cubebs  are  attributed  to  Cubeba  officinalis  (Miquel,)  and  not  to  Piper 
cubeba.  Cubeba  canina  is  also  said  to  yield  a  part  of  the  commercial 
drug.    These  plants  grow  wild  in  Java  and  the  Moluccas. 
The  chemistry  of  castor  oil  does  not  include  the  recent  observations  of 
M.  Bouis  on  the  production  of  sebacic  acid  and  sebacic  ethers,  probably 
because  they  were  pubished  too  late  to  be  noticed  by  the  author. 
Tapioca  is  referred  to  the  Manihot  utilissima  of  Pohl,  instead  of  Janipha 
manihot.    Dr.  Pereira  describes  the  oil  of  cinnamon  leaves,  thus  : 
