156 
ON  SOME  SACCHARINE  SUBSTANCES. 
2|  times  as  easily  as  the  other.  The  most  readily  soluble  por- 
tion contains  the  compound  of  the  active  alcohol,  which,  when 
prepared  from  this  compound,  rotates  the  plane  of  polarization 
about  20°  to  the  left  in  a  cylinder  of  50  centims.  in  height,  whilst 
that  prepared  from  the  less  soluble  baryta-salt  possesses  no  rota- 
tory power. 
These  two  alcohols  are  extremely  interesting,  because  we. may 
treat  one  in  the  same  way  as  the  other,  without  producing  any 
essential  difference.  The  author  has  found  a  difference  in  the 
specific  gravity.  The  active  alcohol  is  about  one-hundredth 
heavier  than  the  other.  From  this  it  follows  that  an  equal 
volume  of  the  two  bodies  cannot  contain  the  same  number  of 
atoms.  The  active  boils  at  260°-6  to  262° 4  F.,  the  inactive  at 
264°-2  F.    Mixtures  of  the  two  boil  at  intermediate  temperatures. 
The  separation  of  the  two  baryta-salts  only  requires  15  to  20 
recrystallizations.  The  salt  of  the  active  alcohol  is  concentrated 
in  the  mother-liquor.  The  difficulties  of  the  separation  lie  en- 
tirely in  the  isomorphism  of  the  two  salts.  Hence  the  two  salts 
unite  in  all  proportions,  and  it  is  only  the  great  difference  in 
their  solubility  that  causes  their  separation.  This  isomorphism 
is  exceedingly  deserving  of  notice,  because  it  proves  that  a  dis- 
symmetry may  be  present  and  not  present  in  the  molecular  state 
of  two  salts,  whilst  a  priori  we  should  conclude  that  this  would 
constitute  an  insuperable  barrier  to  the  union  of  the  molecules  of 
two  salts,  so  as  to  crystallize  together.  The  author  long  supposed 
that  he  had  to  do  with  two  completely  different  salts  of  sulphamy- 
late  of  baryta,  until  he  convinced  himself  that  it  w7as  otherwise. 
Chem.  Gfaz.  from  Comptes  Mendus. 
ON  SOME  SACCHARINE  SUBSTANCES. 
By  M.  Berthelot. 
1.  The  Australian  manna  (Manna  of  the  Eucalyptus)  contains 
a  crystallizable  sugar,  which  was  prepared  in  1843  by  Johnston, 
and  regarded  by  him  as  grape-sugar,  C12H12012-f  2HO.  Accord- 
ing to  Berthelot's  experiments,  this  is  a  peculiar  kind  of  sugar, 
for  which  he  proposes  the  name  of  melitose. 
The  reactions  of  this  body  agree  for  the  most  part  with  those 
of  cane-sugar.    It  appears  to  consist  of  two  isomeric  bodies,  of 
