130 
Yellow  Mercuric  Oxide. 
/ Am.  Jour.  Pharm. 
I      March,  1887. 
YELLOW  MERCURIC  OXIDE. 
By  L.  W.  Hawkins. 
My  attention  was  lately  directed  to  the  difficulty  in  obtaining  pure 
yellow  mercuric  oxide.  When  I  say  pure  I  mean  perfectly  pure. 
No  doubt  most  samples  obtained  are  all  that  could  be  desired  pharma- 
ceutically.  But  speaking  chemically,  I  have  not  come  across  a  sample 
that  answered  either  of  the  tests  required  by  the  British  Pharmacopoeia. 
These  tests  are  that  it  should  entirely  volatilize  when  heated  to  incipient 
redness,  and  that  it  should  dissolve  in  hydrochloric  acid,  by  which  I 
understand  to  dissolve  completely. 
Of  seven  samples  obtained  from  different  sources,  each  left  a  residue 
when  heated  to  low  redness.  Although  these  residues  appeared  con- 
siderable in  the  crucible,  the  percentage  proved  very  small  on  weigh- 
ing. As  was  expected  they  were  chiefly  composed  of  sodium  chloride, 
the  bye-product  in  the  preparation,  with  a  little  sulphate.  Three  of 
them  gave  evidence  of  a  trace  of  potassium,  and  No.  2  contained  a 
little  iron,  while  No.  7  contained  magnesium  as  well. 
Every  sample  failed  to  dissolve  entirely  in  dilute  hydrochloric  acid, 
the  insoluble  portion  being  a  white  powder.  This,  on  being  separated 
was  found  to  be  calomel,  indicating  the  presence  of  mercurous  oxide 
in  the  original  powder.  With  dilute  nitric  acid  a  better  solution  was 
effected,  but  in  every  case  there  was  a  small  amount  of  insoluble 
matter,  consisting  of  a  layer  of  white  powder  which  collected  on  the 
bottom  of  the  test  tube.  This  at  first  seemed  strange,  as  every  sub- 
stance found  in  the  ash  would  be  readily  soluble  in  nitric  acid.  It 
soon  occurred  to  me  however  that  the  mercurous  oxide  present, 
together  with  the  small  quantity  of  sodium  chloride,  would,  in  the 
presence  of  acid  form  mercurous  chloride,  which  is  insoluble  in  cold 
nitric  acid. 
By  the  Pharmacopoeia  process  for  the  preparation  of  yellow  mer- 
curic oxide,  40  fluidounces  of  liquor  soolse  are  ordered,  while  about 
27  would  do  the  work  theoretically.  This  excess  of  sodium  hydrate 
entirely  prevents  the  occurrence  of  any  other  compound  of  mercury 
than  oxide,  and  also  gets  rid  of  such  impurities  as  lead  and  tin,  should 
they  be  present,  by  precipitating  them  as  hydrates  and  redissolving 
them. 
The  mercurous  oxide  was  estimated  by  treating  a  weighed  amount 
of  the  sample  with  dilute  hydrochloric  acid  until  all  the  yellow  color 
