4         MOLECULAR  DISSYMMETRY  OP   ORGANIC  PRODUCTS. 
simple  color,  and  goes  on  increasing  with  the  refrangibility,  ac- 
cording to  a  determined  law.  M.  Biot  also  made  the  very 
curious  observation  that,  of  the  plates  obtained  from  different 
spieces  of  quartz,  there  were  some  which  deviated  the  planes  of 
polarization  to  the  right  and  some  to  the  left,  following  the 
same  laws. 
But  the  most  remarkable  discovery  of  M.  Biot,  in  this  kind 
of  phenomena,  is,  without  contradiction,  that  of  the  deviation 
imparted  to  planes  of  polarization  by  a  great  number  of  natural 
organic  products,  essence  of  turpentine,  solutions  of  sugar,  of 
camphor,  of  tartaric  acid,  &c.  The  first  announcement  of  this 
fact  is  found  in  the  bulletin  of  the  Philomathic  Society  for 
"December,  1815. 
For  the  understanding  of  this  lecture,  we  should  especially 
notice  the  existence  of  the  rotary  property  in  tartaric  acid,  and 
its  absence  in  paratartaric  or  racemic  acid,  an  acid  which 
is  isomeric  with  tartaric  acid. 
There  exists  then  liquid  organic  products  or  solutions  in  water 
which  possess  the  rotary  property,  and  in  this  respect  remind 
us  of  the  solid,  crystallized  quartz.  But  it  is  essential  to  note 
here  that  this  analogy  to  quartz  is  entirely  apparent.  There 
was  in  both  cases  deviation  of  the  plane  of  polarization,  but  the 
characters  of  the  phenomenon  were  very  different. 
Quartz  deviates,  but  it  must  be  crystallized.  Dissolved  or 
solid,  and  not  crystallized,  it  has  no  action.  Not  only  must  it 
be  crystallized,  but  it  must  be  cut  in  plates  perpendicular  to  the 
axis.  From  the  moment  the  plate  is  a  little  inclined  in  the 
direction  of  the  ray,  the  action  abates  and  then  ceases. 
Sugar  deviates,  (and  what  I  say  of  sugar  is  true  of  all  other 
organic  products),  but  the  sugar  must  be  either  dissolved,  or 
solid  and  amorphous  like  barley  sugar.  In  the  crystallized  state 
it  is  impossible  to  discover  any  action. 
The  tube  containing  the  solution  of  sugar  may  be  inclined. 
The  deviation  does  not  change  for  the  same  thickness.  Further, 
by  violently  agitating  the  liquid  by  the  assistance  of  a  clock- 
work movement,  the  phenomenon  remains  the  same. 
Thus  M.  Biot  concluded  from  the  beginning,  strictly  that  the 
action  exerted  by  organic  bodies  was  a  molecular  action,  pecu- 
liar to  their  ultimate  particles,  dependent  upon  their  individual 
