14 
MOLECULAR  DISSYMMETRY  OP  ORGANIC  PRODUCTS. 
polarization  afforded  one  of  the  surest  means  of  obtaining  know- 
ledge of  the  molecular  constitution  of  bodies. 
VI. 
Let  us  return  to  the  two  acids  which  furnish  the  two  kinds  of 
crystals  so  unexpectedly  deposited  by  the  crystallization  of  the 
double  paratartrate  of  soda  and  ammonia.  Nothing,  I  repeat, 
is  more  interesting  than  the  study  of  these  acids. 
In  fact,  one  of  the  two,  that  which  is  derived  from  crystals 
of  the  double  salt  hemihedric  to  the  right,  deviates  to  the  right, 
and  is  identical  with  the  ordinary  tartaric  acid.  The  other 
deviates  to  the  left  like  the  salt  which  furnishes  it.  The  devia- 
tion impressed  by  these  two  acids  upon  the  planes  of  polarization 
is  rigorously  the  same  in  absolute  value.  The  right  acid  follows 
in  its  deviation  particular  laws  which  no  active  body  had  yet 
presented.  The  left  acid  offers  them  in  the  most  faithful 
manner  in  inverse  sense,  without  a  suspicion  of  the  smallest 
difference. 
And  the  proof  that  paratartaric  acid  is  the  combination, 
equivalent  to  equivalent  of  these  two  acids,  is,  that  if  we  mix, 
as  I  am  about  to  do  before  your  eyes,  solutions  somewhat  con- 
centrated of  equal  weights  of  each  of  them,  their  combination 
is  accompanied  by  a  disengagement  of  caloric,  and  the  liquid 
solidifies  at  once  by  an  abundant  crystallization  of  paratartaric 
acid,  identical  with  the  natural  paratartaric  acid.* 
Relatively  to  their  chemical  and  crystallographic  properties, 
whatever  may  be  done  with  one  of  these  acids,  can  be  repeated 
with  the  other  under  the  same  conditions,  and  in  all  cases  we 
obtain  identical  products,  but  not  superposable,  products  which 
are  as  like  as  is  the  right  hand  to  the  left.  The  same  forms, 
the  same  faces,  the  same  angles,  hemihedric  in  both  cases.  The 
only  dissimilarity  is  in  the  right  or  left  inclination  of  the 
hemihedric  facettes,  and  in  the  direction  of  the  rotary  power. 
VII. 
It  is  manifest,  from  all  these  results,  that  we  have  to  deal 
with  two  isomeric  bodies,  whose  general  relations  of  similitude 
and  molecular  dissimilitude  are  known. 
*This  beautiful  experiment  called  forth  applause  from  the  audience. 
