Quantitative  Methods. 
A  in.  Jour.  Pharm. 
April,  191 1. 
and  its  salts,  remove  the  ointment  base  by  means  of  the  proper 
solvent,  dissolve  the  residue  with  nitric  acid,  and  apply  the  method 
as  given. 
Method  No.  3. 
Suggested  by  Mr.  B.  L.  Murray. 
(See  Smith — Electro-Analysis,  pages  90  and  94.) 
Applicable  to  solutions  of  mercury  nitrate,  the  mercury  oxides, 
metallic  mercury,  mercury  with  chalk,  and  possibly  some  of  the 
other  mercurial  preparations. 
Not  applicable  to  calomel  or  corrosive  sublimate. 
Those  preparations  of  mercury  as  found  in  the  U.S. P.,  which 
can  readily  be  brought  into  solution  in  nitric  acid,  are  satisfactorily 
assayed  for  mercury  by  electrolysis. 
The  sample  may  well  be  of  such  a  size  that  the  final  weighing 
of  the  metallic  mercury  will  show  a  weight  of  about  0.250  gramme. 
The  mercury  solutions,  or  the  dry  preparations  dissolved,  are 
acidulated  with  3  c.c.  of  concentrated  nitric  acid,  diluted  to  125 
c.c,  heated  to  70°  C,  and  then  electrolyzed  with  a  current  of 
N.D. 100=0. 06  ampere  and  two  volts.  The  metal  will  be  fully 
precipitated  in  from  2  to  4  hours,  and  may  appear  as  a  uniform 
metallic  coating  upon  the  platinum  dish,  which  is  used  as  a  cathode, 
or  it  may  appear  in  shiny  droplets.  After  the  deposition  of  the 
material  is  complete,  the  mercury  is  washed  with  water,  then  with 
alcohol,  then  with  ether,  and  finally  dried  a  short  time  in  the 
dessicator  and  weighed.  The  electrolyte  remaining  may  be  tested 
qualitatively  for  mercury  to  show  that  the  deposition  was  complete. 
The  time  may  be  materially  shortened  by  the  use  of  the 
rotating  anode  and  mercury  cathode. 
Method  No.  4. 
Suggested  by  Mr.  F.  O.  Taylor. 
(See  E.  Rupp,  Berichte,  1906,  39,  3702.) 
(See  also  Chem.  Zeit.,  1910,  34,  229.) 
A  solution  of  the  mercury  salt,  containing  about  0.2  gramme 
of  mercury  in  25  to  50  c.c.  of  solution,  is  treated  with  excess  of 
KI  so  that  the  Hgia  formed  redissolves.  Render  alkaline  with 
NaOH ;  treat  with  3  c.c.  of  40  per  cent,  formaldehyde  solution 
