298 
Lead  in  Tartrates. 
Am,  Jour.  Pharm. 
June,  1894. 
taric  acid  is  white,  crystalline,  soluble  in  nitric  acid  and  an  excess  of 
tartaric  acid,  also  in  a  solution  of  ammonium  tartrate,  in  which  it 
solidifies  to  a  gelatinous  mass  on  concentration. 
The  salt  was  prepared  by  the  writer  by  precipitating  both  lead 
nitrate  and  acetate  with  potassium  tartrate. 
Thus  prepared,  the  salt  is  almost  completely  insoluble  in  water,  in 
which  it  differs,  as  already  stated,  from  the  citrate. 
It  is  readily  soluble  in  dilute  nitric  acid,  less  so  in  acetic  acid, 
but  dissolves  to  some  extent  in  a  concentrated  solution  of  any  solu- 
ble tartrate. 
The  degree  of  concentration  apparently  influences  the  solubility 
to  an  extent. 
If  such  a  solution  is  allowed  to  stand,  the  lead  salt  is  slowly 
reprecipitated. 
This  also  takes  place  if  the  concentrated  solution  is  diluted  with 
water. 
The  fact  that  insoluble  tartrates  dissolve  in  the  presence  of  alkali 
tartrates  is  illustrated  in  the  case  of  cream  of  tartar,  which  contains 
calcium  tartrate,  and  is  doubtless  present  due  to  this  cause. 
Singularly,  lead  tartrate  is  readily  soluble  in  a  solution  of  potas- 
sium citrate,  from  which,  however,  it  soon  reprecipitates  on  stand- 
ing, as  in  the  case  of  citrate  of  lead. 
To  summarize,  the  following  statements  may  be  made  regarding 
commercial  tartrates : 
Tartrates  prepared  directly  from  the  acid  are  more  liable  to  the 
presence  of  lead  than  when  prepared  from  cream  of  tartar  or  similar 
sources. 
This  has  been  the  writer's  experience,  while  preparing  a  series  of 
alkali  tartrates  for  comparison  with  the  commercial  salts,  and  for 
determining  the  solubility  of  the  lead  salt. 
Cream  of  tartar  apparently  possesses  a  greater  degree  of  purity 
as  regards  the  presence  of  metals  than  tartaric  acid. 
Finally,  the  citrates  appear  to  be  more  liable  to  contain  lead  than 
the  tartrates. 
This  is  readily  explained,  as  the  former  are  usually  prepared 
directly  from  the  acid,  while  in  the  case  of  tartrates,  cream  of  tartar 
appears  to  be  the  source  from  which  they  are  prepared  on  the  com- 
mercial scale. 
