Am.  jour.  Pharm.  j     Lead  in  Medicinal  Zinc  Oxide. 
Aug.  19 1 7.  -* 
355 
least,  is  to  dissolve  5  grammes  of  the  sample  of  zinc  oxide  in  a  slight 
excess  of  diluted  sulphuric  acid,  with  gentle  heat ;  collect  and  wash 
the  precipitate  with  distilled  water ;  then  pour  through  the  filter 
containing  the  precipitate  a  concentrated  solution  of  ammonium 
acetate  (about  25  per  cent.)  freshly  made,  and  to  this  filtrate 
which  now  contains  the  lead  in  a  soluble  form  add  a  slight  excess 
of  solution  of  potassium  chromate  which  will  precipitate  insoluble 
lead  chromate  which  may  be  collected  on  counterpoised  filters,  or  on 
a  Gooch  crucible  mat,  washed,  dried,  weighed  and  calculated  as  to 
its  percentage.  A  more  expeditious  method  which  gives  very  good 
results  with  the  amount  of  lead  usually  found  at  the  present  time 
is  to  simply  dissolve  5  or  10  grammes  of  the  sample  in  an  excess 
of  acetic  acid  and  then  perform  the  precipitation  with  potassium 
chromate  in  this  solution  directly,  and  collect,  wash  and  weigh  the 
precipitate  as  before.  This  latter  modification  will  give  low  results, 
however,  where  part  of  the  lead  is  present  in  the  form  of  sulphate, 
as  is  often  the  case,  as  the  sulphate  will  remain  behind  when  the 
solution  is  made  in  acetic  acid. 
It  would  seem  to  be  advisable  for  pharmacists  to  make  an 
inspection  of  their  stocks  of  zinc  oxide  and  to  firmly  reject  all 
samples  containing  lead  in  excess  of  the  U.  S.  P.  requirements.  If 
this  be  generally  done  the  manufacturers  of  zinc  oxide  will  have  to 
find  some  way  of  supplying  the  pharmaceutical  trade  with  the  lead- 
free  zinc  oxide  to  which  they  have  been  accustomed  and  to  which 
they  are  entitled.  Just  as  long  as  pharmacists  continue  to  take 
whatever  is  offered  to  them,  no  matter  how  plainly  it  may  be  labeled 
as  to  deviation  from  the  official  requirements,  just  as  long  will  this 
sort  of  thing  continue.  Zinc  oxide  containing  from'  0.1  to  0.5  per 
cent,  of  lead  is  certainly  not  a  proper  article  to  use  in  making  the 
ointment,  and  concerted  action  on  the  part  of  pharmacists  all  over 
the  country  would  bring  about  a  speedy  improvement  of  this 
condition. 
