THE  AMEEIOAN 
JOURNAL  OF  PHARMACY 
JANUARY,  1Q14 
THE  ASSAY  OF  MERCURIC  CHLORID  TABLETS. 
^^^_^B/Robert  M.  Chapin, 
Bureau  of  AmmaTlndustry,  U.  S.  Department  of  Agriculture. 
At  the  present  time  mercuric  chlorid  tablets,  especially  those 
prepared  after  the  well-known  Wilson  formula,  are  very  widely 
used,  and  are  used  moreover  with  implicit  confidence  in  the  accuracy 
of  their  declared  content  of  mercuric  chlorid  under  circumstances 
whic*h  render  such  accuracy  a  matter  of  considerable  importance  to 
individual  welfare  and  to  the  public  health  in  general.  There  can 
be  no  question  of  the  desirability  of  assay  methods  which  shall  be 
fairly  accurate,  yet  simple  and  rapid  enough  to  be  freely  used  by 
manufacturers,  pharmacists,  hospitals,  and  sanitary  officials  at  a 
minimum  of  expense  and  chemical  equipment. 
Several  years  ago  Rupp  1  proposed  a  rapid  method  for  the  deter- 
mination of  mercury  in  various  compounds,  involving  the  following 
steps :  ( 1 )  Reduction  to  metallic  mercury  by  formaldehyde  in  alkaline 
solution  in  presence  of  potassium  iodid ;  (2)  solution  of  the  precipi- 
tated mercury  in  excess  of  standard  iodin  solution  after  acidification 
with  acetic  acid ;  and  (3)  titration  of  excess  iodin  by  standard  sodium 
thiosulphate.  A  modification  of  the  method  is  now  official  in  the 
German  Pharmacopoeia  for  the  assay  of  tablets  composed  of  mer- 
curic and  sodium  chlorids. 
In  this  country  Smith  2  has  thoroughly  studied  the  Rupp  method 
when  applied  to  pure  mercuric  chlorid,.  obtaining,  when  certain  modi- 
1  Rupp,  E.  Ueber  die  volumetrische  Bestimmung  des  Quecksilbers.  Be- 
richte  der  Deutschen  Chemischcn  Gesellschaft,  Vol.  39,  No.  14,  pp.  3702-3704. 
Berlin,  Nov.  10,  1906. 
2  Smith,  Carl  E.  Volumetric  determination  of  mercury.  American 
Journal  of  Pharmacy,  Vol.  83,  No.  7,  pp.  311-315.    Phila.,  July,  191 1. 
(1) 
