COMMERCIAL  HYDRARGYRUM  CUM  CRETA. 
45 
dried,  considerable  matter  (which  was  insoluble  in  acetic  acid) 
was  noticed,  supposed  to  be  silica ;  on  this  account  the  weight  of 
the  contents  of  the  filter  would  not  represent  the  quantity  of 
metallic  mercury  in  the  preparation ;  the  filter  was  therefore  in- 
troduced into  a  tube,  closed  at  one  end  ;  the  other  end  of  the 
tube  was  then  drawn  out,  bent  and  broken  off;  it  was  so  adjusted 
that  the  orifice  just  dipped  in  water  contained  in  a  short  test- 
tube.  Heat  was  now  applied  until  globules  ceased  to  come  over  ; 
the  tube  was  then  heated  to  redness  throughout,  and  if  any 
globules  were  noticed  at  the  end  of  the  tube  after  cooling,  they 
were  rinsed  through  with  a  little  alcohol.  The  distilled  mercury 
was  washed  with  alcohol  to  free  it  from  empyreumatic  products, 
dried  and  weighed. 
The  filtrate  was  now  highly  diluted  and  hydrochloric  acid 
added  in  slight  excess;  the  sub-chloride  formed  was  collected  on 
a  tared  filter,  dried  and  weighed.  Sulphuretted  hydrogen  was 
conducted  through  the  filtrate  from  this  precipitate  until  it  was 
saturated ;  the  resulting  sulphide  was  collected  on  a  tared  filter, 
washed,  dried  at  212°,  and  weighed.  The  amount  of  oxides 
present  was  now  easily  calculated  from  the  weight  of  the  pre- 
cipitates. Each  of  the  samples  was  tested  for  sugar  by  Fehling's 
method  (vide  Fres.  Quan.  Analysis),  but  one  sample  contained 
traces  of  sugar. 
Under  the  microscope  the  difi'erence  in  the  mode  of  prepara- 
tion of  the  samples  could  be  very  distinctly  seen.  In  the  sam- 
ples made  by  the  trituration  process  the  chalk  was  observed  to 
be  in  a  much  finer  state  of  division,  and  the  globules,  especially 
in  the  specimens  containing  most  oxide,  were  observed  to  be  in 
irregular  coalescent  masses,  with  particles  of  chalk  intermixed. 
Globules  were  observed  in  some  of  the  samples  coated  with  a  red 
substance,  and  on  others  a  black  powder  was  noticed  ;  this  would 
correspond  to  the  red  and  black  oxides.  In  the  mercury  and 
chalk  made  by  the  succussion  process  the  globules  were  spheri- 
cal, with  clean,  bright  surfaces,  the  largest  of  these  globules 
measuring,  by  the  micrometer,  of  a  millimetre  ;  the  globules 
in  the  preparation  made  by  trituration  were  somewhat  smaller, 
the  largest  measuring  from  200      5^0     ^  millimetre. 
The  results  of  the  investigations  are  tabulated  below. 
