10        MOLECULAR  DISSYMMETRY  OF  ORGANIC  PRODUCTS. 
between  the  circular  polarization  of  quartz  and  that  of  tartaric 
acid,  ought  not  to  be  neglected. 
We  are  now,  thanks  to  the  new  facts  which  precede,  and  to 
the  approximations  which  I  have  just  enumerated,  in  possession 
of  a  preconceived  idea,  (for  it  is  as  yet  nothing  more,)  on  the 
possible  correlation  of  hemihedrity   and  the  rotary  power  of 
the  tartrates. 
Very  desirous  to  find  in  experiment  a  corroboration  of  this 
still  speculative  proof,  my  first  thought  was  to  ascertain  whether 
the  very  numerous  crystallizable  organic  products,  which  possess 
the  molecular  rotary  property,  have  hemihedric  crystalline 
forms,  which  no  one  suspected,  notwithstanding  the  approxima- 
tion of  Herschell.  This  investigation  had  the  success  which  I 
anticipated  for  it. 
I  occupied  myself  also  with  the  examination  of  the  crystal- 
line forms  of  paratartaric  acid'  and  its  salts,  substances  iso- 
meric with  tartaric  combinations,  but  all  of  which  M.  Biot 
found  inoperative  upon  polarized  light.  None  was  found  hemi- 
hedric. 
The  idea  of  the  correlation  of  hemihedrity,  and  the  molecular 
rotary  power  of  natural  organic  products,  gained  ground. 
I  was  soon  led  to  develope  it  clearly  by  a  very  unexpected 
discovery. 
IV. 
It  is  necessary  to  submit  here  a  very  remarkable  note  from 
M.  Mitscherlich,  which  was  communicated  to  the  Academy  of 
Sciences  by  M.  Biot.    Here  it  is  :— 
<<  The  paratartrate  and  tartrate  (double)  of  soda  and  ammonia 
have  the  same  chemical  composition,  the  same  crystalline  form 
with  the  same  angles,  the  same  specific  weight,  the  same  double 
refraction,  and  consequently  the  same  angle  of  optical  axes. 
Dissolved  in  water  their  refraction  is  the  same.  But  the  dis- 
solved tartrate  turns  the  plane  of  polarized  light  and  the  para- 
tartrate is  indifferent,  as  M.  Biot  found  through  the  series  of 
these  two  genera  of  salts.  But,  adds  M.  Mitscherlich,  here  the 
nature  and  the  number  of  atoms,  their  arrangement  and  their  dis- 
tances, are  the  same  in  the  two  compared  bodies.'''' 
This  note  of  M.  Mitscherlich  deeply  interested  me  at  the 
