456    PROCESS  FOR  QUANTITATIVE  ESTIMATION  OF  MERCURY. 
The  flow  of  blood  from  leech-bites  is  best  checked  by  compres- 
sion with  lint,  or  the  introduction  of  cone-shaped  plugs  of  it  into 
the  wound,  by  means  of  a  probe  ;  the  usual  haemostatics  may  also 
be  used. 
It  is  not  recommended  that  leeches  once  used  be  preserved ; 
but  if  they  are  kept  for  future  use,  they  should  not  be  stripped 
between  the  fingers  nor  placed  upon  salt  (the  first  kills  them 
outright,  and  the  second  blisters  them)  but  they  should  be  placed 
in  a  jar  apart  from  those  not  used,  changing  the  water  occa- 
sionally, and  when  they  have  digested  the  blood  they  are  gorged 
with,  they  will  generally  bite  readily  again. 
It  is  thought  by  many  that  the  bite  of  a  leech  once  used  for 
bleeding  a  person  suffering  of  an  infectious  disease,  may  be  the 
means  of  communicating  it  to  others.— Peninsular  and  Inde- 
pendent Medical  Journal,  July,  1858. 
PROCESS  FOR  QUANTITATIVE  ESTIMATION  OF  MERCURY 
ASSOCIATED  WITH  FATTY  BODIES. 
By  Earnest  Nickles. 
Several  methods  have  been  recommended  in  books  for  esti- 
mating mercury  when  mixed  with  fat,  as  is  required  to  be  done 
in  examining  mercurial  ointment. 
Some  of  these  processes  involve  an  inconvenient  amount  of 
manipulation  ;  others,  more  expeditious,  consist  either  in  get- 
ting rid  of  the  mercury  and  fat  by  means  of  heat,  and  then 
weighing  the  residue,  which  consists  of  foreign  matter,  or  in 
simply  indicating  whether  or  not  the  ointment  has  been  falsified, 
without  attempting  to  determine  the  nature  or  importance  of 
the  falsification,  by  immersing  a  small  piece  of  the  ointment  in 
sulphuric  acid  of  66°  mixed  with  two  parts  of  water. 
The  method  which  I  propose,  presents  the  advantages  of  in- 
volving but  little  manipulation,  while  it  affords  the  means  of  es- 
timating very  exactly  the  ingredients  which  are  present.  It  is 
formed  on  the  principal  I  have  already  made  known  in  my  com- 
munication on  the  purification  of  amorphous  phosphorus.  A 
mixture  being  formed  of  two  substances  of  different,  densities, 
to  separate  these  by  means  of  a  liquid  of  intermediate  density, 
in  such  a  way  that  the  lighter  substance  may  float  over  the 
