Am.  Jour.  Pharm. 
Sept.,  1889. 
Reduction  of  Tartaric  Acid. 
491 
water-bath ;  after  a  short  time  a  greenish-yellow  precipitate,  consisting 
chiefly  of  the  iron  salt  of  an  acid  containing  more  oxygen  than  isoar- 
abinic  acid,  is  formed.  The  whole  is  then  evaporated  with  constant 
stirring,  until  the  residue  solidifies  on  cooling,  and  is  then  extracted 
with  strong  alcohol.  The  alcohol  is  evaporated,  the  residue  dissolved 
in  water,  the  solution  neutralized  with  milk  of  lime,  filtered,  evaporated 
to  a  syrup,  and  the  calcium  salt  which  separates  dissolved  in  water  and 
decomposed  with  the  calculated  quantity  of  oxalic  acid.  The  filtered 
solution  is  concentrated,  mixed  with  alcohol,  separated  from  any  un- 
decomposed  salt,  and  again  concentrated  and  mixed  with  alcohol  and 
ether.  After  keeping  for  a  long  time,  a  crystalline  compound,  which 
the  author  names  isoarabinic  acid  hydrate-  separates,  and  the  filtered 
solution,  on  evaporation,  yields  isoarabinic  acid. 
Isoarabinic  acid,  C6H10O5,  is  a  thick,  almost  colorless  syrup,  which 
is  miscible  with  water  in  all  proportions,  and  when  burnt  gives  off  a 
smell  of  burnt  sugar.  It  is  dextrorotatory,  and  its  specific  rotatory 
power  is  [a]D=-f  20°,  but  it  does  not  reduce  Fehling's  solution.  The 
potassium  salt,  C6H905K,  is  anhydrous,  and  crystallizes  well.  The 
calcium  salt,  (C6H905)2Ca-f  9H20,  dissolves  in  water,  forming  a  sticky 
solution,  from  which  it  crystallizes  moderately  easily;  it  loses  some  of 
its  water  at  100 — 120°,  the  remainder  only  at  a  temperature  so  high 
(above  140°)  that  the  salt  is  partially  decomposed.  It  reduces  am- 
moniacal  silver  solution,  and  readily  decomposes  both  in  solution  and 
in  the  dry  state,  being  converted  into  a  basic  salt,  (C6H905)2Ca,CaO  + 
8H20.  The  latter  is  a  colorless  powder,  and  is  insoluble  in  water, 
but  it  dissolves  in  potash,  and  is  reprecipitated  on  boiling  the  solution ; 
it  reduces  ammoniacal  silver  solution.  When  a  solution  of  the  cal- 
cium salt  is  mixed  with  a  solution  of  lead  acetate,  a  yellow  precipi- 
tate, consisting  principally  of  the  salt,  (C6H905)2Pb,  is  formed,  and  a 
colorless  substance,  consisting  principally  of  the  basic  salt,  (C6H905) 
2Pb,2PbO,  separates  from  the  filtrate  after  some  time. 
Isoarabinic  acid  hydrate  (see  above)  has  probably  the  composition 
C6H1206 ;  it  does  not  reduce  Fehling's  solution. 
These  results  show  that  substances,  isomeric  with  the  carbohydrates, 
and  other  compounds  richer  in  oxygen,  are  formed  by  the  action  of 
ferrous  sulphate  on  tartaric  acid.  The  quantity  of  ferrous  sulphate 
employed  may  be  as  little  as  one-tenth  the  weight  of  the  tartaric  acid 
without  influencing  the  results,  but  the  author  believes  that  direct 
sunlight  may  have  some  appreciable  effect  on  the  reaction.    These  facts 
