176  Presence  of  Lead  in  Citrates.  {Am'I^n.mt"m- 
Lead  citrate  was  prepared  by  the  writer,  with  a  view  of  determin- 
ing its  solubility  in  water,  by  two  methods,  first  by  saturating  boiling 
solution  of  citric  acid  with  the  official  lead  carbonate,  and  second  by 
the  decomposition  of  lead  acetate  by  a  purified  solution  of  potas- 
sium citrate. 
In  the  saturation  process  the  lead  citrate  precipitated  as  soon  as 
formed,  with  evolution  of  C02. 
After  cooling,  the  supernatant  liquid  was  filtered  from  the  precipi- 
tate, and  on  examination  gave  heavy  precipitates  with  reagents  for 
lead.  This  would  indicate  that  lead  citrate,  prepared  by  satura- 
tion, is  soluble  in  water  to  some  extent. 
Precipitated  Salt. — The  salt,  prepared  by  precipitation,  was  care- 
fully washed  to  remove  the  potassium  acetate. 
The  washings,  even  if  they  were  made  repeatedly  until  no  sign  of 
the  acetate  remained,  invariably  gave  indication  of  the  presence  of 
lead. 
Subsequent  examination  of  the  dry  salt  showed  it  to  be  slightly 
soluble  in  water. 
The  addition  of  an  excess  of  potassium  or  any  other  soluble  citrate 
greatly  favors  solution  of  the  salt. 
If  a  solution  containing  lead  citrate  with  an  excess  of  potassium 
citrate  is  allowed  to  stand,  the  salt  will  again  deposit  in  a  mass  of 
soft  crystals  after  a  short  time. 
This  also  takes  place,  if  the  official  solution  of  magnesium  citrate 
is  substituted  for  the  potassium  salt. 
The  same  experiments  were  repeated  with  the  citrate,  prepared 
from  lead  nitrate  in  place  of  the  acetate,  with  identi  ~  \  results. 
The  statement  of  the  insolubility  of  lead  citrate  »  water  must 
therefore  be  accepted  as  not  being  invariably  the  case,  especially  in 
the  presence  of  other  citrates. 
If  the  lead  present  in  commercial  samples  of  potassium  citrate 
exists  in  the  form  of  this  salt,  its  ready  indication  upon  the  applica- 
tion of  reagents  to  perfectly  clear,  aqueous  solutions  is  explained. 
COMMERCIAL  CITRATES. 
Potassium  Salt. — The  presence  of  metallic  lead  has  already  been 
mentioned,  but  it  has  been  found  by  the  writer,  that  whenever  it 
was  present  as  deposit  in  an  aqueous  solution  of  the  salt,  the  latter 
also  contained  the  metal  in  a  soluble  form. 
