426 
Oxidation  of  Milk  Sugar. 
f  Am.  Jour.  Pharm. 
\     August,  1889. 
for  another  48  hours,  a  stream  of  air  is  passed  through  the  solution  to 
drive  off  most  of  the  free  bromine,  the  remainder  being  converted  into 
hydrobromic  acid  by  passing  hydrogen  sulphide  into  the  cooled  solu- 
tion. The  quantity  of  hydrobromic  acid  present  having  been  ascer- 
tained by  titrating  a  portion  of  the  solution  with  silver  nitrate,  the 
calculated  quantity  of  lead  carbonate  is  added,  and  the  hydrobromic 
acid  remaining  in  the  filtered  solution  is  carefully  precipitated  with 
silver  oxide.  The  solution  is  filtered,  treated  with  hydrogen  sulphide, 
and  the  filtrate  evaporated.  The  acid,  syrupy  liquid  thus  obtained  is 
agitated  for  a  long  time  with  large  quantities  of  cold  glacial  acetic  acid 
to  remove  reducing  substances  and  other  products,  the  colorless  resi- 
due, the  weight  of  which  is  about  one-third  that  of  the  lactose  em- 
ployed, is  dissolved  in  water  and  the  warm  solution  precipitated  with 
a  hot,  concentrated  solution  of  basic  lead  acetate.  The  solution  of 
basic  lead  acetate  is  prepared  by  dissolving  the  neutral  salt  (2  parts) 
and  lead  hydroxide  (1  part)  in  hot  water  (3  parts)  and  dissolving  the 
crystals,  which  separate  on  cooling,  in  pure,  hot  water.  The  precipi- 
tated lead  salt  is  quickly  separated  by  filtration,  washed  with  hot  water, 
and  then  suspended  in  cold  water  and  decomposed  with  hydrogen  sul- 
phide. The  filtrate  is  evaporated  on  a  water-bath  in  a  partial  vacuum, 
*  the  residue  treated  with  alcohol  and  ether  to  remove  acetic  acid,  and 
finally  dissolved  in  a  small  quantity  of  water  and  reprecipitated  with 
alcohol  and  ether. 
Lactobionic  acid  is  a  colorless,  strongly  acid  syrup,  and  is  very 
readily  soluble  in  water,  but  only  very  sparingly  in  alcohol  and  glacial 
acetic  acid,  and  is  insoluble  in  ether.  It  decomposes  carbonates,  but 
does  not  reduce  Fehling's  solution  even  on  boiling.  The  calcium, 
(C12H21012)2Ca,  barium,  (C12H21012)2Ba,  cadmium,  and  had  salts  were 
prepared  by  warming  an  aqueous  solution  of  the  acid  with  the  corres- 
ponding carbonate  ;  they  are  all  insoluble  in  alcohol,  but  readily 
soluble  in  water  excepting  the  basic  lead  salt.  On  evaporating  the 
aqueous  solution  over  sulphuric  acid,  the  salts  are  obtained  in  the  form 
of  syrups  which  gradually  solidify  but  do  not  clearly  show  a  crystal- 
line structure. 
Lactobionic  acid  is  decomposed  into  galactose  and  gluconic  acid 
when  warmed  with  dilute  mineral  acids.    The  pure  acid  was  heated 
.at  100°  for  an  hour  with  5  per  cent,  sulphuric  acid ;  the  gluconic 
acid  was  then  isolated  by  means  of  the  barium  salt,  and  identified  by 
1  Berichte,  xxii.,  361—364 ;  Jour.  Chem.  Soc,  May,  1889. 
