458    PROCESS  FOR  QUANTITATIVE  ESTIMATION  OF  MERCURY. 
If  it  is  desired  to  determine  the  nature  of  any  foreign  mat- 
ter present,  this  must  be  separated  from  the  liquids  by  filtration. 
The  quantity  of  fusible  metal  to  be  used  is  not  a  matter  of 
indifference.  ,  If  the  quantity  be  too  small  in  proportion  to  the 
mercury,  the  alloj  will  not  solidify  on  cooling.  The  proportion 
which  answers  well,  is  six  or  eight  times  the  weight  of  the  mer- 
cury supposed  to  be  present  in  the  ointment. 
It  is  also  desirable  to  dilute  the  solution  of  chloride  of  calcium 
after  having  decanted  off  the  sulphide  of  carbon.  If  the  solu. 
tion  is  too  dense,  the  fused  metals  divide  into  globules,  and  do 
not  readily  unite  again,  but  if  the  solution  is  diluted  with  an 
equal  volume  of  water,  the  union  of  the  metals  will  instantly 
take  place. 
This  very  expeditious  process  is  at  the  same  time  very  exact ; 
it  affords  the  means  of  recovering  all  the  mercury,  especially  if 
care  be  taken  to  use  sulphide  of  carbon  that  does  not  contain 
sulphur  in  solution. 
I  have  always  recovered  in  this  way  very  nearly  the  whole  of 
the  mercury  which  I  had  intimately  mixed  with  fat,  both  in  ex- 
perimenting with  those  ingredients  alone,  and  also  when  foreign 
bodies,  such  as  powdered  graphite  or  sulphide  of  antimony,  has 
been  added. 
May  it  not  be  inferred,  from  the  facility  with  which  the  amal- 
gamation of  the  fusible  metal  takes  place,  under  the  circumstan- 
ces described,  that  the  whole  of  the  mercury  in  mercurial  oint- 
ment is  in  the  metallic  state  ?  In  reference  to  this  point  I  have 
made  comparative  experiments,  in  which  a  certain  quantity  of 
oxide  of  mercury  was  mixed  with  the  fat,  and  after  removing  the 
fat  in  the  way  already  described,  I  have  found  that  combination 
between  the  mercury  and  the  fusible  metal  does  not  take  place 
immediately  ;  in  fact,  it  is  only  after  applying  a  boiling  temper- 
ature for  some  hours  that  a  certain  part  of  the  mercury  enters 
into  combination,  and  even  then  by  displacing  an  equivalent 
quantity  of  the  fusible  metals,  which  are  separated  as  oxides. 
On  separating  the  oxides  by  filtration,  and  applying  appropri- 
ate tests,  the  presence  of  bismuth,  lead  and  tin,  as  well  as  mer- 
cury, are  easily  detected.  In  operating  on  good  mercurial  oint- 
ment, not  only  does  the  amalgamation  take  place  immediately, 
but  no  separation  of  metallic  oxide  occurs.    This  proves,  I  think, 
