Am.  Jour.  Pharm ,  ) 
Feb.,  1875.  j 
Examination  of  Citrates,  etc. 
61 
This  may  be  done  by  adding  silver  nitrate  in  dilute  solution  in  the  cold: 
the  precipitate  (citrate,  tartrate)  being  washed  on  a  filter  with  several 
small  portions  of  distilled  water.  (A  portion  is  soluble  in  nitric  acid  ; 
not  chloride.)  If  sugar  be  not  present,  tartrate  may  be  identified  by  the 
blackening  when  heated.  In  presence  of  sugar,  the  precipitate  should 
be  decomposed  by  hydrosulphuric  acid  gas  and  the  silver  sulphide  filtered 
out.  The  filtrate  is  now  neutralized  with  potassa,  and  calcium  chlo- 
ride is  added  :  a  precipitate  in  the  cold  indicates  tartaric  acid.  The 
mixture  (or  the  filtrate)  is  boiled  ;  a  resulting  precipitate  indicates  citric 
acid.  These  precipitates  are  now  treated  with  cold  concentrated  potassa 
solution  ;  a  solution,  gelatinous  when  boiled  and  liquid  when  again  cold, 
indicates  tartaric  acid  ;  non-solution  indicates  citric  acid,  the  precipitate 
being  soluble  in  cupric  chloride  solution. 
Estimation  of  Citric  Acid  in  absence  of  Sulphuric  and  Tartaric  Acids. — 
a.  As  calcium  citrate.  Neutralize  the  solution  ;  add  sufficient  cal- 
cium chloride  solution  ;  boil  for  some  time  (to  change  the  precipitate 
from  the  amorphous  to  the  crystaline  state),  collect  on  a  tared  filter  ; 
wash;  dry  at  120°  to  150°  C.  (248°  to  302°  F.)  and  weigh.  Cag 
(C,HP,),  :  2H3C,H,0,  :  :  i  :  077108,  or  Ca3(C,H,0,),  :  2H3C, 
HAHP  :  :  I  :  0-84337- 
h.  By  precipitation  as  barium  citrate,  from  barium  acetate,  in  alcohol 
of  60  to  95  per  cent.,  for  weighing  as  barium  sulphate. — J.  Creuse  : 
Am.  Jour.  Phar..^  xliii  (1871),  537. 
If  sulphates  are  present.^  the  sulphuric  acid  should  be  determined  by 
precipitation  with  barium  chloride  in  presence  of  hydrochloric  acid,  and 
the  resulting  barium  sulphate  deducted  from  the  total  barium  sulphate 
obtained  according  to  the  preceding  paragraph. 
Estimation  of  Tartaric  Acid  in  absence  of  Sulphuric  and  Citric  Acid.^  {and 
other  Acids  forming  insoluhle  Lead  Salts.) — Ammonium  salts  should  not  be 
present,  a.  The  solution,  very  slightly  acidulated  with  acetic  acid,  is 
precipitated  with  lead  acetate  solution,  and  the  precipitate  is  washed  on 
a  tared  filter  with  dilute  alcohol,  and  dried  on  the  water-bath.  PbC^H^Og 
:  H^C.H^Og  :  :  I  :  0*422535, 
If  sulphates  are  present,  the  sulphuric  acid  should  be  estimated  by 
itself,  and  its  equivalent  quantity  of  lead  sulphate  deducted  from  the 
weight  obtained  according  to  the  preceding  paragraph. 
b.  Tartaric  acid  may  also  be  determined  as  a  calcium  salt.  For  this 
purpose,  the  neutral  solution  is  treated  with  chloride  of  calcium  in  sfight 
