60  Lithium  Benzoate  and  Salicylate.  {A£ebv°u£y*mm' 
I  was  always  of  the  opinion  that  lithium  benzoate  was  acid 
to  litmus.  Such,  however,  is  not  the  case.  The  excess  of  ben- 
zoic acid  is  probably  volatilized  with  the  aqueous  vapor,  formed 
during  the  process  of  manufacture. 
In  the  Digest  of  criticisms  on  the  U.S.P.,  1890,  Part  II,  p. 
102,  we  find  the  following :  "  The  addition  of  a  drop  of 
ammonia  to  the  ferric  chloride  T.  S.  (fifth  paragraph),  is  neces- 
sitated by  the  slight  acid  reaction  of  the  lithium}-  salt."  Ber- 
zelius  prepared  the  basic  ferric  benzoate  as  directed  by  the 
U.S.P.  The  reason  for  adding  the  ammonia  is  not  apparent.  It 
cannot  be  to  neutralize  the  acidity  of  the  ferric  chloride  solution, 
for,  when  the  basic  iron  benzoate  is  formed,  hydrochloric  acid  is 
liberated,  which,  in  turn,  liberates  benzoic  acid. 
The  voluminous  precipitate  formed  when  a  ferric  chloride  solu- 
tion is  added  to  an  aqueous  solution  of  lithium  benzoate  or  any 
other  neutral  soluble  benzoate,  is  but  flesh-colored  or  light  brown, 
rather  than  brownish-pink. 
Under  this  chemical  two  sets  of  tests  are  given  for  chlorides  and 
sulphates.  One  set  allows  a  limit  of  both  impurities,  the  other  set 
excludes  them  rigidly.  The  first  set  does  not  add  quite  enough 
nitric  acid  to  remove  all  the  benzoic  acid,  which  interferes  with  the 
chloride  test.  In  the  second  set  the  tests  are  to  be  applied  to  a  5 
per  cent,  aqueous  solution,  without  previous  removal  of  the  benzoic 
acid.  The  addition  of  silver  nitrate  to  this  solution  causes  a  pre- 
cipitate of  silver  benzoate.  Barium  benzoate  is  sufficiently  soluble, 
so  that  the  above  concentration  could  be  employed  in  testing  for 
sulphate,  but  another  procedure  would  be  safer. 
On  adding  a  slight  excess  of  hydrochloric  acid  to  a  5  per  cent, 
aqueous  solution  of  the  salt,  a  voluminous  white  precipitate  of  ben- 
zoic acid  is  formed,  which,  after  being  separated  by  filtration  and 
thoroughly  washed  and  dried,  should  respond  to  the  tests  given 
under  benzoic  acid.  If  to  a  small  portion  of  the  filtrate,  a  few 
drops  of  barium  chloride  solution  are  added,  not  more  than  a 
very  slight  turbidity  should  result  (limit  of  sulphate). 
On  evaporating  the  remaining  filtrate  to  dryness,  1  part  of  the 
residue  should  be  soluble  in  5  parts  of  absolute  alcohol,  and  the 
addition  of  an  equal  volume  of  ether  should  not  produce  a  turbid- 
ity (limit  of  other  alkalies).    A  2  per  cent,  aqueous  solution  of  the 
1  Italics,  L.  F.  K. 
