AmAJp0rUiir;i?94arm'}        Presence  of  Lead  in  Citrates.  175 
(1)  The  above  neutral  solution. 
(2)  Was  acidulated  with  citric  acid. 
(3)  Was  allowed  to  become  alkaline  by  prolonged  contact  with 
potassium  bicarbonate. 
To  each  portion  particles  of  metallic  lead  were  added  and  allowed 
to  remain  in  contact  from  24  to  48  hours. 
The  solutions  were  then  filtered  and  examined  for  lead  in  the  usual 
manner.  • 
Each  revealed  the  presence  of  lead,  showing  that  the  citrate,  either 
in  neutral,  acid,  or  alkaline  state,  exerted  a  solvent  action  upon  the 
metal. 
In  the  preparation  of  the  salt  on  the  large  scale  several  factors  may 
be  the  means  of  rendering  the  lead  in  commercial  citric  acid  soluble, 
and  each  possibility  may  be  considered  in  turn. 
It  has  already  been  stated  that  citric  acid  alone  has  a  solvent 
action  upon  the  metal,  which  is  increased  by  heat. 
The  neutral  salt  itself  in  solution  has  some  solvent  power  also. 
The  alkaline  condition  favors  the  action  upon  the  metal  and  this 
is  perhaps  the  most  frequent  source  of  the  impurity  of  the  commer- 
cial salts. 
The  Pharmacopoeia  directs  potassium  citrate  to  have  a  neutral  or 
faintly  alkaline  reaction. 
In  the  greater  number  of  instances  the  commercial  salt  was  found 
to  be  alkaline,  which  is  probably  due  to  the  employment  of  potas- 
sium carbonate  in  its  manufacture. 
Still  another  source  may,  perhaps,  be  found  in  the  evolution  of 
C02  during  the  saturation  process. 
It  is  well-known  that  water  saturated  with  C02  and  in  contact 
with  lead  in  its  metallic  state,  is  invariably  found  to  contain  the 
metal  after  a  time. 
This  source  is,  however,  not  likely  in  this  case. 
Citrate  of  Lead. — The  question  may  be  asked,  in  what  form  the 
metal  exists  in  citrates,  and  the  logical  conclusion  is — as  lead  citrate. 
This  salt  is  stated  by  most  text-books  to  be  insoluble  in  water. 
According  to  Watts'  Dictionary  of  Chemistry  the  salt,  if  prepared 
by  double  decomposition  between  lead  nitrate  and  sodium  citrate, 
crystallizes  with  3  molecules  of  water. 
An  acid  citrate,  which  is  stated  to  be  crystalline  and  very  soluble 
in  water,  is  also  mentioned  together  with  several  others. 
