34  Recent  Work  in  the  Sugar  Group.     {Am  ja"iffiarm" 
of  the  latter,  this  is  separated  into  the  osazones  of  two  sugars 
named  a-  and  ^-acrose,  to  denote  their  source.  By  the  action  of 
lime  or  some  other  oxides  on  formaldehyde,  condensation  of  the 
latter  is  brought  about  and  a  mixture  of  sugars  results,  containing 
chiefly  a-acrose  and  another  termed  formose.  This  a-acrpse  is  the 
starting  point  for  preparing  a  number  of  other  sugars.  On  reduction 
with  sodium  amalgam  it  yields  an  alcohol  C10H]4O6,  which  is  an 
optically  inactive  form  of  mannitol.  The  latter  substance,  called 
i-mannitol,  when  oxidized  with  nitric  acid  gives  i-mannose,  isomeric 
with  glucose,  and  by  further  oxidation  a  monocarboxylic  acid, 
i-mannonic  acid,  is  obtained.  By  fractional  crystallization  of  the 
strychnine  and  morphine  salts  of  this  acid  it  may  be  separated  into 
dextro-  and  laevo-rotatory  mannonic  acids. 
On  heating  d-mannonic  acid  with  quinoline  it  is  partly  converted 
into  the  isomeric  d-gluconic  acid,  and  by  reduction  of  the  latter, 
ordinary  d-glucose  is  obtained.  If  d-mannonic  acid  is  reduced  with 
sodium  amalgam,  d-mannose  is  formed :  from  this  by  further 
reduction  is  obtained  ordinary  d-mannitol.  If  d-mannose  is  heated 
with  phenylhydrazine  acetate,  an  osazone  is  formed  identical  with 
that  obtained  from  glucose  ;  if  this  osazone  is  treated  with  strong 
hydrochloric  acid,  the  hydrazine  is  regenerated  and  a  substance  is 
formed  having  the  formula  C6H10O6,  called  glucosone ;  this  is  the 
aldehyde  of  fructose,  and  on  reduction  it  yields  a-fructose  (ordinary 
laevo-rotatory  fruit-sugar).  If  the  osazone  is  prepared  from  glucose 
and  treated  in  this  way,  conversion  of  glucose  into  fructose  is 
effected. 
The  i-mannonic  acid  which  is  obtained  with  d-mannonic  acid  on 
splitting  up  the  inactive  acid  by  means  of  its  strychnine  salt,  yields 
on  reduction  1-mannose  and  1  mannitol. 
If  a-acrose  is  fermented  by  yeast,  it  is  separated  into  two 
oppositely  active  substances,  the  laevo-rotatory  component  being 
broken  up  by  the  yeast,  and  the  dextro-rotatory  being  left  unaffected  ; 
the  latter  is  found  to  be  1-fructose,  showing  that  a-acrose  is  i-fructose. 
On  hydrolyzing  the  cyanhydrin  of  arabinose  (pentose  C5H10O5, 
obtained  by  the  action  of  sulphuric  acid  on  acacia  and  other  gums), 
a  mixture  of  1-gluconic  and  1-mannonic  acids  is  obtained.  From 
the  former  1-glucose  is  obtained  by  reduction,  and  by  mixing  this 
with  an  equal  quantity  of  d-glucose,  i-glucose  results,  from  which 
the  inactive  alcohol    may  be    prepared.    Similarly,  from  equal 
