Am.  Jour.  Pharm. ) 
April,  1911.  ; 
Quantitative  Methods. 
191 
Method 
Chemist.  No.  2. 
Per  cent. 
Mr.  L.  D.  Havenhill   944o" 
94.19 
94-65 
91.88 
97.65 ' 
98.80' 
97.65 ' 
91.88' 
93.95  ' 
Mr.  F.   O.  Taylor 
16 
Method 
Method 
No.  3, 
No.  4. 
Per  cent. 
Per  cent. 
97.83  ' 
64.1  " 
97.94  " 
98.64  " 
99.89  " 
97.64  " 
98.86 
98.80 
98.86 
99.58'' 
99.98  " 
99.80 
99.70 
99.62 
100.50 
21 
10 
22 
Method  Method 
No.  5.  No.  6. 
Per  cent.  Per  cent. 
97.85"  97.98 
93.10  97.84 
98.09  97.60 
94.00  97.51 
Comments. 
'  Precipitating  and  washing  in  dilute  alcohol. 
^  Same  solution  as  preceding®  but  washing  with  water. 
'  Dried  at  50°  C. 
®  Our  work  seems  to  indicate  that  there  was  a  considerable  loss  of 
mercury,  due  to  volatilization  when  the  cathode  was  dried  at  a  temperature 
of  50°. 
Unquestionably  the  electrolytic  method  is  extremely  accurate  when 
used  by  one  who  is  experienced  and  has  at  hand  the  proper  apparatus,  and 
it  can  also  be  made  a  very  rapid  method.  It  does  not  seem,  however, 
to  be  suited  to  the  requirements  of  pharmacopceial  estimation,  as  at  the 
present  time  one  is  much  more  likely  to  find  the  requisite  skill  and  apparatus 
for  making  other  forms  of  assay  than  the  electrolytic,  among  those  to  whom 
these  assays  would  be  chiefly  valuable. 
"Dried  in  dessicator  at  room  temperature. 
Mr.  L.  A.  Brown :  I  got  very  poor  results  due  possibly  to  two  causes : 
(i)  Mechanical  loss  of  mercury  in  filtering  after  reduction.  (2)  Part  of 
the  mercury  appears  to  come  down  in  a  colloidal  condition  and  is  lost  in 
the  filtrate.  I  have  proven  to  my  entire  satisfaction  that  the  reduction  by 
formaldehyde  in  alkaline  solution  is  quantitative,  and  what  makes  me 
believe  that  part  of  the  mercury  is  in  a  colloidal  form  is  that  a  perfectly 
clear  filtrate  will  shown  the  presence  of  mercury  by  hydrogen  sulphide  if 
completely  saturated. 
The  method  gave  us  uncertain  results. 
"  Mr.  L.  D.  Havenhill :    The  amount  of  water  used  in  washing  the 
precipitate  of  mercury  iodate  tends  to  vary  the  results. 
Thirty  seconds  with  stirring  for  reduction. 
^'Mr.  F.  O.  Taylor:    We  find  this  method  inaccurate  because  of  the 
distinct  solubility  of  the  mercuric  iodate  in  water,  which  solubility  may 
be  proved  by  testing  the  filtrate  from  the  mercuric  iodate  by  hydrogen 
sulphide,  when  a  very  decided  test  for  mercury  can  be  obtained. 
