5oo 
Zinc  Oxide. 
/  Am.  Tour.  Pharm. 
I-       July,  1 918. 
Since  that  time  some  manufacturers  have  placed  U.  S.  P.  zinc 
oxide  upon  the  market  that  complies  with  the  tests  in  every  respect. 
Hence  the  relevancy  of  the  title  of  the  present  paper. 
A  statement  was  made  in  the  former  paper  that  it  was  difficult 
to  obtain  satisfactory  results  with  the  U.  S.  P.  heavy  metal  test  when 
applied  to  zinc  compounds.  A  number  of  samples  have  been  exam- 
ined during  the  past  year  and  subsequent  experience  leads  to  the 
conclusion  that  the  test  for  lead  in  zinc  oxide  by  the  present  heavy 
metals  test  might  well  be  eliminated  and  replaced  by  the  following: 
Add  2  grammes  of  zinc  oxide  to  5  mils  of  distilled  water  and 
then  add  25  mils  of  diluted  sulphuric  acid  and  heat  on  the  water 
bath  with  constant  stirring  for  five  minutes.  The  resulting  solu- 
tion should  be  colorless  and  free  from  opalescence  or  turbidity  (cop- 
per and  lead). 
Add  2  grammes  of  zinc  oxide  to  20  mils  of  distilled  water  and 
after  stirring  well  add  5  mils  of  glacial  acetic  acid  and  warm  upon 
the  water  bath  until  solution  is  effected.  The  addition  of  5  drops 
of  potassium,  chromate  T.S.  produces  no  turbidity  nor  precipitate 
(lead). 
Samples  of  zinc  oxide,  U.  S.  P.,  found  upon  the  market  at  the 
present  time  will  answer  both  of  these  tests  perfectly  and  they  are 
much  easier  to  apply  and  base  an  opinion  upon  the  results  than  is 
the  heavy  metals  test  previously  referred  to. 
Considerable  correspondence  has  been  carried  on  with  manufac- 
turers of  zinc  oxide  relative  to  the  presence  of  lead  and  the  amount 
found.  One  well-known  imported  brand  which  has  enjoyed  a  high 
reputation  for  years  was  found  to  contain  0.28  per  cent,  of  PbO. 
The  U.  S.  P.  heavy  metals  test  under  the  most  favorable  conditions 
will  detect  about  0.05  per  cent,  of  PbO.  The  suggested  tests  will 
permit  the  presence  of  not  more  than  0.03  per  cent,  of  PbO  and  this 
requirement  is  being  met  by  several  manufacturers  at  the  present 
time  and  is  a  fair  requirement  under  the  circumstances  and  one 
which  should  be  attained  by  all  manufacturers  of  zinc  oxide. 
It  may  be  well  to  state  for  the  benefit  of  pharmacists  whose  prod- 
ucts are  constantly  open  to  inspection  and  analysis,  with  subsequent 
prosecution  and  unpleasant  publicity  when  articles  are  found  below 
the  U.  S.  P.  standards,  that  the  tests  above  described  may  be  easily 
applied  to  the  zinc  oxide  separated  from  the  official  ointment  of  zinc 
oxide.  I  would  suggest,  therefore,  also  that  to  the  text  for  the 
latter  the  following  paragraph  be  added : 
