314  Vohimctric  Dctcrmiuafion  of  Mercury. 
Ointinciit  of  Aininoniated  Mercury. — Consists  of  lo  per  cent,  of 
ammoniated  mercury  and  white  vaseline.  Heat  about  5  Gm.  of 
the  ointment,  accurately  weighed,  in  a  small  flask  with  25  c.c.  of  12.5 
per  cent,  hydrochloric  acid  on  a  water  bath.  Mix  frequently  by 
rotating  the  flask  during  10  minutes.  Pour  the  acid  liquid  into  a 
100  c.c.  flask,  rinse  the  vaseline  and  flask  repeatedly  with  water  and 
dilute  the  combined  liquid  and  washings  to  100  c.c.  Transfer  25  c.c. 
to  a  glass-stoppered  flask,  add  i  Gm.  of  potassium  iodide  and  pro- 
ceed further  as  directed  for  the  assay  of  mercuric  chloride  tablets. 
Each  c.c.  of  n/io  iodine  solution  consumed  corresponds  to  0.01257 
Gm.,  approximately,  of  ammoniated  mercury. 
Mercuric  Salicylate. — Contains  about  55  per  cent,  of  mercury. 
Dissolve  about  0.3  Gm.  of  the  salt,  accurately  weighed,  in  dilute 
sodium  hydrate  solution,  acidulate  with  acetic  acid,  and  add  25  c.c. 
of  n/io  iodine  solution.  Let  the  mixture  stand  in  a  closed  flask 
for  3  hours  at  room  temperature,  rotating  it  occasionally.  Titrate 
the  excess  of  iodine  with  n/io  sodium  thiosulphate  solution.  Each 
c.c.  of  n/io  iodine  solution  consumed  corresponds  to  0.0100  Gm.  of 
mercury. 
Mercury  Plaster. — Contains  20  per  cent,  of  mercury ;  made  with 
lead  plaster,  wool  fat  and  yellow  wax.  Heat  about  3  Gm.  of  the 
plaster  mass,  accurately  weighed,  with  20  c.c.  of  nitric  acid,  sp.  gr. 
1.38  to  1.40,  in  a  flask  having  a  wide  neck  and  connected  with  a 
reflux  condenser.  Heat  about  10  minutes  or  until  mercury  globules 
are  no  longer  visible  in  the  sandy  deposit  of  lead  nitrate,  add  25  c.c. 
of  water  and  heat  again  until  the  fat  has  separated,  leaving  the 
aqueous  layer  clear.  Cool  and  pour  the  solution  through  a  tuft 
of  absorbent  cotton  into  a  100  c.c.  flask.  Break  up  the  disk  of  fat, 
rinse  it  and  the  flask  with  4  or  5  portions  of  5  c.c.  each  of  water  and 
to  the  combined  liquids  add  potassium  permanganate  until  perma- 
nently red  or  until  brown  flakes  separate.  Decolorize  or  clarify  the 
solution  by  addition  of  ferrous  sulphate  solution  and  dilute  to  100  c.c. 
To  25  c.c.  of  the  solution  add  2  c.c.  of  a  10  per  cent,  solution  of 
ferric  alum  and  titrate  with  n/to  ammonium  sulphocyanate.  Each 
c.c.  consumed  corresponds  to  o. 01000  Gm.  of  mercury. 
Mercury  Ointment. — Contains  30  per  cent,  of  mercury ;  made 
with  wool  fat,  peanut  oil,  lard,  and  mutton  tallow.  Proceed  as 
directed  for  the  assay  of  mercury  plaster,  using  about  2  Gm.  of  the 
ointment  and  20  c.c.  of  nitric  acid. 
