^'"*ja°n"i88r''''}        Oxldcs  ill  Mercurictl  Preparations,  49 
fresh  sample  of  pilula  hydrargyri  I  added  to  it  5  per  cent,  of  freshly 
precipitated  mercurous  oxide,  and  submitted  portions  of  this  mass  to  a 
careful  analysis  by  the  method  em])loyed  by  Messrs.  Dechan  and 
Maben,  and  by  the  hydrocyanic  acid  method  I  have  described.  The 
results  were : 
Hydrocyanic  acid  method  4*72  p.c.  HggO. 
Messrs.  Dechan  and  Maben's  method   *250  " 
Although  there  is  no  doubt  more  than  one  source  of  error  in  the 
process  of  Messrs.  Dechan  and  Maben  which  contributes  to  this  result, 
there  can  be  little  doubt  that  the  most  important  one  is  the  instability 
of  mercurous  acetate  in  presence  of  organic  matter,  especially  glucose, 
it  being  rapidly  reduced  even  at  ordinary  temperatures  to  oxide,  a 
change  which  would  be  still  more  readily  brought  about  by  hot  diges- 
tion. In  support  of  this  explanation  of  the  opposite  results  obtained 
by  Messrs.  Dechan  and  Maben  and  myself  is  the  fact  that  in  hydrar- 
gyrum cum  creta,  a  preparation  free  from  organic  matter  and  which, 
in  my  experience,  is  less  liable  to  oxidation  than  pilula  hydrargyri  or 
unguentum  hydrargyri,  their  process  gives  results  coinciding  very 
closely  with  my  own  and  those  of  other  workers  on  the  same  subject. 
When  I  completed  my  examination  of  blue  pill  in  1876  I  preserved 
samples  of  each  mass  analysed,  and  thinking  the  present  opportunity  a 
fitting  one,  I  have  again  estimated  the  quantity  of  oxides  in  one  of 
these  samples  which  eight  years  ago  contained  '24  per  cent,  of  mer- 
curic oxide  and  '62  per  cent,  of  mercurous  oxide,  but  which  I  now 
find  to  contain  1'20  per  cent,  of  mercuric  oxide  and  3'62  per  cent,  of 
mercurous  oxide,  thus  affording  another  proof  of  the  theory  that  the 
oxides  of  mercury,  which  undoubtedly  exist  in  all  samples  of  pilula 
hydrargyri,  increase  with  the  age  of  the  sample. — Pliar.  Jour,  and 
Trans.,  November  8,  1884,  p.  363. 
In  the  discussion  upon  the  foregoing  paper  Mr.  Umney  stated  that 
a  sample  of  blue  pill  made  about  six  months  had  contained  about  2 
per  cent,  of  mercurous  and  1*2  ])er  cent,  of  mercuric  oxide.  Blue  pill 
made  by  machinery  is  slightly  contaminated  with  iron,  and  this  react- 
ing with  the  astringent  principle  of  rose  leaves  may  cause  a  change  of 
color.  Blue  pill  is  generally  made  by  triturating  metallic  mercury 
with  confection  of  roses  in  the  bed  of  a  large  mill,  the  stones  being  of 
granite  and  a  sweeper  frequently  made  of  iron  following  the  stones  in 
their  circuit.  Mr.  Umney  prepares  gray  powder  in  a  similar  manner 
by  triturating  well  dried  prepared  chalk  with  mercury  under  granite 
stones,  the  process  for  100  pounds  occupying  seven  or  eight  hours. 
4 
