48 
Oxides  in  Mercurial  Preparations. 
Am  Jour.  Pharm. 
Jan.,  1886. 
mercuric  sulphide.  From  the  weight  of  these  salts^  after  drying,  is 
calculated  the  amount  of  oxides  present  in  the  sample. 
The  method  which  I  have  used  for  the  estimation  of  the  oxides  in 
the  pharmacopceial  preparations  of  mercury  is  first  to  digest  the  sample 
in  hydrochloric  acid  to  dissolve  the  mercuric  oxide ;  to  this  solution, 
after  neutralizing  excess  of  acid  with  ammonia,  stannous  chloride  is 
added  and  the  reduced  metallic  mercury  separated,  dried  over  sulphuric 
acid  and  weighed  ;  from  this  weight  is  calculated  the  amount  of  mer- 
curic oxide  present.  To  estimate  the  mercurous  oxide  a  fresh  portion 
of  the  sample  is  digested  in  a  5  per  cent,  solution  of  hydrocyanic  acid, 
which  converts  the  mercury  of  the  mercuric  oxide  into  mercuric  cyanide 
and  also  so  converts  half  the  mercury  of  the  mercurous  oxide,  leaving 
the  remainder  as  metallic  mercury.  The  hydrocyanic  acid  solution  is 
treated  with  stanno'us  chloride,  in  the  same  manner  as  the  hydrochloric 
acid  solution,  and  from  the  weight  of  metallic  mercury  obtained  the 
weight  of  mercury  existing  as  mercuric  oxide  is  subtracted,  and  the  re- 
mainder doubled,  this  result  calculated  into  mercurous  oxide  gives  the 
quantity  present  in  the  sample.  Tiiis  method  for  the  estimation  of 
mercurous  oxide  is  based  on  some  observations  of  Scheele  on  the  action 
of  hydrocyanic  acid  on  oxides  of  mercury,  and  is  more  fully  described 
in  my  paper  on  "The  Composition  of  Pilula  Hydrargyria'  ("  Pharm- 
Journ.,"  Febiuary  5,  1876).  In  that  paper  I  gave  the  results  of  the 
examination  of  nine  commercial  samples  of  pilula  hydrargyri,  the 
oxides  in  which  were  estimated  by  the  method  I  have  just  described. 
In  each  case,  with  one  exception,  the  age  of  the  sample  was  determined 
as  accurately  as  possible.  The  age  of  the  samples  varied  from  eighteen 
hours  to  two  years,  and  the  percentage  of  oxides  from  a  trace  to  1'80 
of  mercuric  oxide,  ancl  from  '25  to  4*22  of  mercurous  oxide.  The 
proportion  of  oxides  })resent  bore  such  a  striking  relation  to  the  age  of 
the  samples  as  to  lead  me  to  the  conclusion  that  the  proportion  of 
oxides  increases  with  the  age  of  the  sample,  and  that  machine-made 
masses  oxidize  more  rapidly  than  those  made  by  hand. 
After  trying  Messrs.  Dechan  and  Maben's  method  on  some  com- 
mercial samples  of  pilula  hydrargyri,  and  failing  to  find  but  a  trace  of 
oxides  in  them,  while  by  the  method  which  I  had  formerly  used  I  found 
distinct  quantities,  I  decided  to  try  the  two  methods  on  a  sample  con- 
taining a  known  quantity  of  one  of  the  oxides.  As  mercurous  oxide 
exists  in  mercurial  preparations  to  a  much  greater  extent  than  mercuric 
I  considered  it  the  most  suitable  for  the  purpose,  and  after  preparing  a 
