Am.  jour,  pharm.  \  Mercuric  Chlorid  Tablets.  5 
January,  1914.    j  ^ 
ought  therefor  to  include  an  estimation  of  ammonium  chlorid,  espe- 
cially when  a  simple  and  convenient  method  is  available. 
The  method  for  ammonium  chlorid  here  adopted  is  an  adaptation 
of  the  process  of  Ronchese,4  which  is  based  on  the  reaction  between 
formaldehyde  and  a  neutral  ammonium  salt,  whereby  methylenamin, 
(CH2)fiN4,  is  formed,  the  acid  originally  contained  in  the  ammo- 
nium salt  being  released  and  becoming  titratable  with  standard 
caustic  alkali  and  phenolphthalein.  The  strengths  of  reagents,  etc., 
recommended  by  Wilkie  5  have  been  adopted. 
Titration  by  standard  alkali  and  phenolphthalein  can  not  of 
course  be  conducted  in  presence  of  mercuric  chlorid.  This  difficulty, 
however,  is  easily  overcome  by  throwing  the  mercury  into  a  complex 
ion  through  the  addition  of  potassium  iodid.  The  method  is  as  fol- 
lows:  Into  each  of  two  150  c.c.  Erlenmeyer  flasks  pipette  5  c.c.  (one- 
fourth  tablet)  of  the  tablet  solution  previously  prepared  for  the  esti- 
mation of  mercuric  chlorid  (5  tablets  per  100  c.c.)  and  add  to  each 
flask  2  c.c.  of  a  20  per  cent,  solution  of  potassium  iodid. 
Dilute  one  volume  of  37  per  cent,  formaldehyde  solution  with 
three  volumes  of  water,  measure  20  c.c.  of  the  mixture  into  a  small 
flask,  add  0.5  c.c.  of  phenolphthalein  indicator  solution,  neutralize 
with  tenth-normal  barium  hydrate  or  caustic  alkali,  then  flow  the 
solution  over  the  sides  of  one  of  the  flasks  (flask  A)  containing  tablet 
solution,  and  mix  well.  To  the  other  flask  (flask  B)  containing  tablet 
solution  add  about  65  c.c.  water. 
Now  add  to  flask  A  25  c.c.  water  and  titrate  with  tenth-normal 
barium  hydrate  or  tenth-normal  caustic  alkali  free  from  carbon 
dioxid  until,  by  using  flask  B  as  a  standard  for  comparison,  a  color 
change  is  perceptible  (titration  A). 
Add  methyl  red  to  flask  B  and  titrate  with  either  tenth-normal 
acid  or  alkali  as  needed  (titration  B). 
To  titration  A  add  titration  B  if  performed  with  acid,  or  subtract 
if  performed  with  alkali.  The  resultant  figure  multiplied  by  the 
factor  0-.0214  for  strictly  tenth-normal  alkali  will  give  the  average 
weight  of  ammonium  chlorid  per  tablet. 
4  Ronchese,  A.  Nouveau  procede  de  dosage  de  rammoniaque.  Journ.  de 
Pharmacie  et  de  Chimie,  Vol.  25,  No.  12,  pp.  611-617.    Paris,  June  16,  1907. 
5  Wilkie,  John  M.  The  Ronchese  method  of  determining  ammonia  and 
its  extension  to  the  determination  of  the  total  acid  content  of  organic  am- 
monium salts  and  ammoniacal  solutions.  Journal  of  the  Society  of  Chemical 
Industry,  Vol.  29,  No.  1,  pp.  6-7.   London,  Jan.  15,  1910. 
