538 
On  Citric  Acid,  Etc. 
f  Am.  Jour.  Pharm. 
t    Dec.  1, 1871. 
alcohol  63°  and  dry  at  a  moderate  heat.  The  precipitate  thus  ob- 
tained represents  all  the  citric  acid  in  the  shape  of  the  citrate  baryta; 
3  Ba  O.C12  with  a  variable  proportion  of  water.    But  this  salt 
is  too  hygrometric  to  give  correct  results  if  weighed  directly ;  it  is 
necessary  to  transform  it  into  sulphate  baryta.  This  is  done  without 
difficulty  by  burning  the  filter  and  heating  the  ashes  and  precipitate 
to  red  heat  with  sulphuric  acid  several  times  till  a  constant  weight  is 
obtained.  This  being  ascertained,  the  weight  of  the  citric  acid  may 
be  calculated  within  two  milligr. 
If  free  citric  acid  is  to  be  evaluated,  a  convenient  quantity  may  be 
first  saturated  with  a  titered  solution  of  caustic  soda  which  gives  gen- 
erally a  little  more  than  the  actual  strength  ;  the  citrate  soda  may  be 
then  treated  in  the  manner  described  above,  which  gives  a  result  a 
little  below  the  truth,  and  the  average  between  the  two  will  be  within 
one  milligr.  of  the  truth. 
If  it  is  necessary  to  evaluate  the  citric  acid  of  a  non-alkaline 
citrate,  soluble  or  otherwise,  the  analysis  is  conducted  in  this  man- 
ner ;  a  certain  weight  of  the  salt,  from  l-5th  to  2-5th  grms.  is  heated 
carefully  with  a  solution  of  caustic  soda  or  potassa  in  excess ;  the 
heat  must  be  applied  long  enough  to  decompose  the  salt  thoroughly, 
but  not  enough  to  alter  the  citric  acid.  The  liquid  is  then  filtered, 
the  filter  washed  as  usual,  and  the  liquor,  exactly  saturated  with 
acetic  acid,  may  be  treated  as  an  alkaline  citrate.  Care  must  be 
taken  in  this  case,  as  in  the  others,  that  the  saturation  be  as  perfect 
as  possible  for  an  excess  of  acetic  acid  causes  the  citrate  baryta  to 
become  soluble  in  alcohol,  and  an  excess  of  alkali  would  precipitate 
some  free  baryta. 
The  solution  of  acetate  of  baryta  used  for  these  analyses  may  be 
prepared  by  treating  pure  diluted  acetic  acid  by  an  excess  of  carbon- 
-ate  of  baryta,  heating  to  ebullition,  adding  some  alcohol  when  cold, 
and  filtering.  This  solution  may  be  filtered  to  contain  five  p.  c.  of 
baryta,  so  as  to  know  very  nearly  how  much  of  it  is  necessary  to  pre- 
cipitate the  alkaline  citrates  thoroughly,  without  too  much  an  excess 
of  the  reagent.  The  addition  of  alcohol  insures  its  keeping  unchanged 
for  an  unlimited  period. 
I  need  not  describe  here  any  analysis  of  citric  acid,  but  I  shall  de- 
scribe the  analysis  of  some  metallic  citrates. 
