570 
Official  Lead  Preparations. 
/Am.  Jour.  Pharm. 
\  November,  1897. 
To  obtain  a  satisfactory  lead  subacetate  solution,  it  is,  therefore, 
necessary  to  employ  only  crystallized  lead  acetate,  free  from  efflor- 
escence or  carbonate,  in  its  preparation. 
The  writer  has  examined  fifteen  samples  of  lead  acetate,  purchased 
in  open  market,  with  avoidance  of  duplication  of  source. 
In  the  course  of  these  examinations  the  advisability  of  introduc- 
ing some  means  of  estimating  the  lead  strength  of  the  salt,  either 
gravimetrical  or  volumetric,  became  apparent,  and  a  consideration 
of  the  subject  may  be  urged  upon  the  Committee  of  Revision 
of  the  Pharmacopoeia. 
The  British  Pharmacopoeia  has  given  directions  for  the  volumetric 
estimation  of  the  salt  by  means  of  sulphuric  acid. 
In  an  examination  of  fifteen  samples  of  lead  acetate,  the  writer 
found  calcium  in  every  specimen  in  varying  amounts. 
As  the  presence  of  this  impurity  may  interfere  slightly  with  an 
accurate  estimation  by  means  of  normal  sulphuric  acid,  decinormal 
potassium  bichromate  solution  was  employed  as  precipitant,  and  the 
number  of  c.c.  necessary  to  precipitate  I  gramme  of  the  salt 
determined. 
This  precipitant  was  suggested  by  the  method  of  F.  Lux  in  the 
valuation  of  red  lead. 
This  author  directs  the  decinormal  solution  to  contain  14761 
grammes  to  I  litre,  each  c.c.  being  equivalent  to  -0207  gramme 
of  lead. 
If  the  decinormal  solution  of  the  U.  S.  Pharmacopoeia,  containing 
14  689  grammes  to  the  litre,  be  employed,  each"  c.c.  is  approxi- 
mately equivalent  to  -02064  of  lead,  and  consequently  0378  of 
lead  acetate. 
Before,  however,  giving  directions  for  a  volumetric  estimation,  a 
standard  of  purity  for  the  acetate  must  be  fixed. 
If  allowance  is  made  for  impurities  amounting  to  2  per  cent.,  we 
•98 
have  the  following  calculation:  .^yg  =  25-9  c.c. 
Nitrate  of  silver  is  used  as  an  indicator  to  determine  the  end 
of  the  reaction,  and  as  a  slight  excess  of  the  bichromate  solution  is 
necessary  for  the  development  of  the  red  silver  chromate,  it  may 
safely  be  made  26  c.c. 
The  following  addition  may,  therefore,  be  recommended  to  the 
Pharmacopoeia : 
