Am.  Joue.  Pharm.  ) 
Dec.  1,  1871.  J 
On  Citric  Acid,  Etc. 
537 
ON  CITRIC  ACID  AND  ANEW  CLASS  OF  COMPOUND  CITRATES. 
By  J.  Creuse*. 
Having  undertaken  the  study  of  the  citrates  as  a  class,  and  espe- 
cially of  those  of  the  citrates  where  the  acid  is  combined  with  more 
than  one  base,  the  first  difficulty  I  met  was  how  to  evaluate  citric  acid 
without  having  recourse  to  the  long  and  complicated  process  of  an  or- 
ganic elementary  analysis.  I  consulted  the  most  recent  publications 
and  some  eminent  chemists  without  obtaining  my  desideratum,  viz.  : 
— How  to  evaluate  citric  acid  free  and  combined,  in  the  same  direct 
manner  as  sulphuric  or  muriatic  acid  ?  The  only  thing  then  left  for 
me  was  to  try  myself  and  find  such  a  process,  in  which  I  succeeded, 
after  many  failures,  including  an  explosion  of  citrate  of  silver. 
This  process  is  founded  on  the  fact  that  while  the  alkaline  citrates,, 
the  alkaline  acetates  and  the  acetate  of  baryta  are  freely  soluble  in 
alcohol  sp.  gr.  0-805  (63°  Tralles),  citrate  of  baryta  is  completely  in- 
soluble in  that  menstruum. 
As  the  presence  of  alkaline  acetates  does  not  interfere  with  the 
reaction,  this  enables  the  chemist  to  evaluate  citric  acid  in  almost  any 
shape,  for  free  citric  acid  may  be  saturated  by  an  alkali,  alkaline 
citrates  may  be  analyzed  directly,  and  other  citrates  may  be  converted 
into  citrate  potassa  without  difficulty.  This  method  presenting  pecu- 
liar features,  I  will  describe  it  in  full. 
If  the  citric  acid  to  be  evaluated  is  in  the  shape  of  an  alkaline 
citrate,  take  from  one  to  two  grammes  of  the  salt,  dissolve  in  10  to 
20  c.c.  of  water,  neutralize  the  solution  with  acetic  acid  if  it  is  alka- 
line, with  ammonia  if  acid  ;  add  a  slight  excess  of  a  neutral  solution 
of  acetate  baryta  and  twice  the  volume  of  the  whole  liquid  of  alcohol 
95°.  Allow  to  rest  twelve  to  twenty-four  hours ;  the  citrate  baryta, 
which  is  at  first  like  a  thick  jelly,  has  by  that  time  become  denser  and 
easier  to  wash.  Transfer  the  whole  to  a  filter  ;  but  as  some  of  the 
precipitate  always  adheres  to  the  sides  of  the  vessel,  it  is  recovered 
thus :  pour  into  the  vessel  ten  to  fifteen  c.c.  of  water,  turn  it  round 
so  as  to  wet  all  the  parts  where  any  salt  adheres  :  citrate  baryta 
being  to  a  certain  extent  soluble  in  water  is  soon  taken  up  ;  add  then 
double  the  volume  of  alcohol  and  pour  on  the  filter  with  the  first  pro- 
duct. This  being  repeated  a  second  time,  all  the  citrate  baryta  may 
be  considered  as  collected  on  the  filter.    Wash  this  thoroughly  with 
*  Reprint,  communicated  by  the  author. 
