2 
Mercuric  Chi  or  id  Tablets. 
f  Am.  Jour.  Pharm. 
\    January,  1914. 
fications  were  introduced,  a  recovery  of  99.8  to  100.3  Per  cent-  of  the 
mercuric  chlorid  employed.  Smith's  modifications  involved  (1) 
the  use  of  a  larger  amount  of  substance  and  reagents  to 
reduce  experimental  errors,  (2)  a  longer  time  of  action  by 
formaldehyde  to  insure  complete  reduction  to  metallic  mercury, 
and  (3)  a  much  less  degree  of  acidification  before  addition  of  iodin, 
since  large  amounts  of  free  acetic  acid  tend  to  produce  low  results. 
Smith  states  that  similarly  good  quantitative  results  were  obtained 
when  the  method  was  applied  to  mixtures  of  mercuric  chlorid  and 
ammonium  chlorid  colored  with  aniline  dyes.  That  is,  the  modified 
method  is  implied  to  be  applicable  to  commercial  tablets  prepared 
after  Wilson's  formula  (mercuric  chlorid,  7.3  grains;  ammonium 
chlorid,  7.7  grains;  coloring  matter,  q.s.). 
In  this  laboratory  Smith's  statements  and  results  were  con- 
firmed on  solutions  of  pure  mercuric  chlorid.  Utter  failure,  however, 
followed  attempts  to  apply  his  method  either  to  commercial  tablets  or 
to  similar  laboratory  mixtures  of  mercuric  and  ammonium  chlorids. 
Abnormal  precipitates  appeared  after  addition  of  iodin,  and  results 
obtained  were  erratic  and  much  too  low.  At  the  same  time  the  method 
given  in  the  German  Pharmacopoeia,  slightly  modified,  was  found 
to  work  smoothly  and  quantitatively. 
The  addition  of  formaldehyde  to  a  solution  of  ammonium  salts 
produces  hexamethylenamin,  which  is  known  to  form  difficultly  solu- 
ble compounds  with  both  iodin  and  mercuric  salts.3  In  Smith's 
modification,  then,  conditions  appear  to  be  such  as  to  permit  the 
formation  and  separation  of  hexamethylenamin  compounds  to  the 
resultant  vitiation  of  the  process,  while  in  the  method  of  the  German 
Pharmacopoeia  the  greater  dilution  at  which  the  process  is  worked 
either  inhibits  the  formation  of  such  interfering  substances,  or,  more 
probably,  is  sufficient  to  retain  them  in  solution  and  hence  in  a  harm- 
less condition.  At  all  events,  if,  in  addition  to  other  minor  modifi- 
cations later  to  be  noted,  a  volume  of  75  c.c.  of  water  is  added  at 
the  time  the  contents  of  the  flask  are  acidified  before  the  addition  of 
iodin,  no  abnormalities  appear  in  the  working  of  Smith's  process, 
and  the  results  are  equally  accurate  in  the  presence  or  absence  of 
ammonium  chlorid. 
Inasmuch  as  the  method  finally  chosen  here  as  most  satisfactory  is 
3  Cohn,  G.  Die  Verbindung  des  Urotropins.  Pharmazeutische  Zentral- 
halle,  Vol.  52,  No.  44,  pp.  1173-1179.    Dresden,  Nov.  2,  191 1. 
