354 
Lead  in  Medicinal  Zinc  Oxide.      (Am  jour.  Pharm. 
Aug.  19 1 7. 
were  now,  as  he  was  then,  dependent  entirely  upon  his  own  exer- 
tions for  his  supply  of  many  of  his  chemicals. 
For  many  years  the  supplies  of  zinc  oxide  entering  the  pharma- 
ceutical trade  were  of  high  quality,  and  while  it  was  necessary  occa- 
sionally to  reject  a  lot,  there  was  not  a  great  deal  of  trouble  in 
obtaining  supplies  which  were  in  full  compliance  with  the  U.  S.  P. 
in  every  respect. 
This  condition  has  recently  changed,  and  I  think  I  can  safely 
assert  that  ninety  per  cent,  of  the  zinc  oxide  on  the  market  at  the 
present  time  will  not  only  not  answer  the  U.  S.  P.  test  for  absence 
of  heavy  metals  but  that  in  the  majority  of  instances  lead  is  present 
in  an  amount  ranging  from  0.1  per  cent,  to  0.5  per  cent,  calculated 
as  metallic  lead. 
This  condition  has  come  about  through  the  well-known  fact  that 
few  if  any  pharmacists  test  their  supplies  and  still  fewer  pay  any 
attention  to  such  statements  of  the  label  as  "  U.  S.  P.  in  all  respects 
except  the  heavy  metal  test." 
No  statement  has  appeared  in  recent  literature  calling  attention 
to  this  condition,  nor  do  the  standards  of  any  of  the  prominent 
pharmacopeias  of  the  world  make  any  allowance  for  such  large 
amounts  of  this  impurity  in  zinc  oxide.  The  latest  editions  of  the 
following  pharmacopeias  were  consulted :  Austrian,  Belgian,  British, 
Danish,  French,  German,  Italian,  Japanese,  Netherland,  Norwegian, 
Swedish,  Swiss,  Spanish  and  our  own  U.  S.  P. 
In  all  of  these  there  is  a  specific  test  for  the  absence  of  lead, 
the  test  being  made  in  a  slightly  acid  solution  of  the  oxide  with  solu- 
tion of  hydrogen  sulphide,  the  requirement  being  that  a  white  pre- 
cipitate be  produced.  The  German  Pharmacopeia  has  in  addition 
a  specific  test  for  absence  of  lead  with  potassium  chromate  solution 
in  an  acid  solution  of  the  oxide. 
In  applying  the  hydrogen  sulphide  test,  found  in  all  of  the 
Pharmacopeias  quoted  above,  some  difficulty  is  often  experienced  in 
observing  the  darkening  due  to  lead  on  account  of  the  interference 
of  the  light  colored  zinc  sulphide  which  comes  down  and  obscures 
the  test  and  frequently  makes  it  necessary  to  add  repeated  amounts 
of  hydrogen  sulphide  and  then  make  the  final  observations  in  com- 
parison with  a  sample  to  which  a  known  amount  of  lead  has  been 
added. 
A  very  satisfactory  method  of  detecting  and  estimating  the  lead 
which  seems  to  be  present  occasionally  as  the  sulphate,  in  part  at 
