12 
MOLECULAR  DISSYMMETRY  OF  ORGANIC  PRODUCTS. 
my  idea.  I  carefully  separated  the  crystals  hemihedric  to  the 
right,  and  the  crystals  hemihedric  to  the  left,  and  observed  their 
solutions  separately  in  a  polarizing  apparatus.  I  then  saw  with 
no  less  surprise  than  pleasure,  that  the  crystals  hemihedric  to 
the  right  deviated  the  plane  of  polarization  to  the  right ;  the 
crystals  hemihedric  to  the  left  deviated  to  the  left,  and  when  I 
took  an  equal  weight  of  the  two  kinds  of  crystals,  the  mixed  solu- 
tion was  neutral  to  light  by  the  neutralization  of  the  two  equal 
and  opposite  individual  deviations. 
Thus  I  set  out  from  the  paratartaric  acid ;  I  obtained  in  the 
ordinary  way  the  double  paratartrate  of  soda  and  ammonia,  and 
after  some  days  the  solution  deposits  crystals,  all  of  which  have 
exactly  the  same  angles,  the  same  aspect  to  such  a  degree,  that 
M.  Mitscherlich,  the  celebrated  crystallographer,  in  spite  of  the 
most  minute  and  severe  study,  could  not  detect  any  difference 
between  them.  The  molecular  arrangement  in  the  two,  however, 
is  entirely  different.  The  rctary  power  as  well  as  the  mode 
of  dissymmetry  attest  it.  The  two  species  of  crystals  are  isomor- 
phous,  and  isomorphous  with  the  corresponding  tartrate  ;  but 
here  the  isomorphism  is  presented  with  a  peculiarity  without  ex- 
ample up  to  this  time  ;  it  is  the  isomorphism  of  two  dissymmetric 
crystals  which  reflect  themselves  in  a  mirror.  This  comparison 
presents  the  fact  in  a  very  just  manner.  In  fact,  if  in  both 
species  of  crystals  I  suppose  the  hemihedric  facettes  prolonged 
until  they  mutually  meet,  I  obtained  two  symmetrical  tetrahe- 
drons inverse,  and  which  cannot  be  superposed  in  spite  of  the 
perfect  identity  of  all  their  respective  parts.  Hence  I  must 
conclude  that  I  had  separated  by  the  crystallization  of  the  double 
paratartrate  of  soda  and  ammonia,  two  atomic  groups  symme- 
trically isomorphous,  intimately  united  in  paratartaric  acid. 
Nothing  is  easier  than  to  prove  that  these  two  species  of  crystals 
represent  two  distinct  salts,  from  which  may  be  derived  two 
different  acids. 
It  is  sufficient  to  proceed,  as  in  all  similar  cases,  to  precipitate 
each  salt  by  a  salt  of  lead  or  barytes,  and  then  to  isolate  the 
acids  by  sulphuric  acid. 
The  study  of  these  acids  possesses  immense  interest ;  I  know 
none  more  interesting. 
But  before  submitting  it,  permit  me  to  present  here  some  notes 
relative  to  their  discovery. 
