192 
Q 1  ( an titative  Methods. 
( Am.  Jour.  Pharni 
X       April,  1911. 
^'  Two  minutes  with  stirring  fcr  reduction. 
^'^  Four  minutes  with  stirring  for  reduction. 
^^Five  minutes  with  vigorous  shaking. 
'°  Mr.  B.  L.  Murray:  In  using  this  method  we  found  that  two  minutes 
was  not  sufficient  time  for  the  reduction  of  the  mercury  by  formaldehyde. 
Even  five  minutes  was  too  short  a  time  and  a  Httle  heat  was  used  to 
complete  the  reduction ;  but  this  we  found  reduced  the  mercury  to  such 
a  condition  that  it  was  very  hard  to  dissolve  in  the  iodine  solution. 
We  found  the  time  for  reduction  to  be  insufficient,  also  the  stirring. 
Better,  or  at  least  higher  results  were  obtained  by  vigorously  shaking  the 
mixture.  The  quantity  of  acetic  acid  used  is  indefinite.  Our  results,  which 
are  not  herein  reported,  seem  to  show  that  the  more  acetic  acid  used,  the 
lower  are  the  results.  We  believe  that  the  size  of  the  factor  is  too  large 
to  permit  of  sufficient  accuracy  when  working  on  samples  that  run  close  to 
TOO  per  cent,  in  purity. 
"  Here  again  the  difficulty  of  dissolving  the  precipitated  mercury  in 
iodine  solution  is  the  chief  drawback.  With  care  the  method  can  be  made 
accurate,  but  it  usually  requires  more  time  than  a  process  of  this  kind 
should. 
In  this  method  the  mercuric  iodide  was  reduced  with  formaldehyde 
in  the  manner  indicated  by  the  method  of  E.  Rupp,  dissolved  in  nitric  acid 
and  precipitated  with  sodium  arsenate.  It  was  noted  that  the  precipitate 
of  mercuric  arsenate  was  not  of  uniform  color.  The  higher  results  here 
reported  were  obtained  from  precipitates  that  were  materially  whiter  in 
color  than  those  (more  yellow)  precipitates  yielding  the  lower  results  which 
were  more  yellow  in  color. 
Inaccurate  results  here  may  be  attributed  to  the  slight  solubility  of 
mercuric  arsenate  in  water,  which  seems  to  be  sufficient  to  render  the 
method  not  very  desirable. 
No  careful  work  was  done  by  me  on  this  method,  but  only  some 
preliminary  tests,  and  it  would  appear  that  special  care  must  be  taken  in 
the  reduction  of  the  mercuric  salts  and  it  is  therefore  preferable  to  use 
phosphorus  acid  instead  of  hypophosphorus  acid. 
Contrary  to  previous  observations  I  find  this  method  to  give  good 
results  if  the  reduction  is  carried  out  in  the  cold  and  not  allowed  to 
stand  too  long  before  adding  iodine  solution.  If  the  reduced  mercury  is 
allowed  to  coalesce  and  form  large  globules  the  solution  of  the  mercury 
in  the  iodine  solution  is  very  slow. 
i 
