THE 
AMERICAN  JOURNAL  OF  PHARMACY. 
SEPTEMBER,    1  8  67. 
PHARMACEUTICAL  NOTES. 
By  C.  Lewis  Diehl. 
Lead  Plaster-. — The  formula  of  our  Pharmacopoeia  directs 
that  the  litharge  be  sifted  into  the  oil,  boiling  water  added,  and 
the  mixture  boiled  until  a  plaster  is  formed,  with  occasional 
addition  of  water.  When  this  direction  is  followed,  it  is  almost 
impossible  to  obtain  a  plaster  perfectly  free  from  uncombined 
litharge,  and  I  do  not  believe  that  it  is  followed  by  manu- 
facturers on  a  large  scale.  I  have  prepared  the  plaster  fre- 
quently during  the  past  three  or  four  years,  and  invariably  suc- 
ceeded in  obtaining  a  handsome  plaster,  entirely  free  from  un- 
combined litharge,  by  first  rubbing  the  sifted  litharge  with  about 
half  its  weight  of  oil,  stirring  this  mixture  into  the  remainder  of 
the  oil,  contained  in  a  tinned  copper  kettle,  adding  the  water, 
and  heating  to  above  212°  F.,  until  a  uniform  plaster  was 
formed,  which  occupied  from  one  to  two  clays.  It  is  not  neces- 
sary to  boil  the  plaster,  which,  requiring  the  application  of 
direct  heat,  is  apt  to  burn  it,  and  therefore  requires  constant 
attention.  I  generally  prepared  it  in  a  steam  kettle,  under  a 
pressure  of  ten  pounds  of  steam,  and  do  not  think  that  the  tem- 
perature ever  rose  above  230°  F.  Its  manufacture  in  small 
quantities  may  be  conducted  on  a  chloride  of  zinc  bath,  and  the 
process  requires  but  occasional  stirring  and  renewal  of  the  water 
as  it  evaporates.    It  is  true  that  when  direct  heat  is  employed, 
