UNGUENTUM  HYJDRARGYRI.  201 
in  a  sample  of  mercurial  ointment  may  sometimes  be  a  subject 
of  importance ;  in  fact,  a  druggist  should  make  sure  of  the 
value  of  every  lot  he  buys,  and  be  satisfied  that  he  keeps  an 
officinal  article. 
Some  place  great  dependence  on  .the  color  and  consistence  of 
the  ointment,  and  if  these  are  as  they  should  be,  and  the  mer- 
cury is  properly  extinguished,  they  feel  satisfied ;  but  these 
appearances  can  easily  be  imitated  by  dishonest  persons,  and  the 
ignorant,  unwary  or  credulous  druggist  might  be  deceived. 
A  surer  and  more  satisfactory  evidence  is  found  in  the  analytic 
test  usually  applied,  that  is,  by  extracting  the  mercury  in  a  free 
state  ^by  distillation ;  we  then  have  a  clear  demonstration,  not 
only  of  the  amount  used,  but  also,  if  any  portion  of  it  has  been 
substituted  by  other  metals  or  impurities. 
From  various  experiments  made  by  the  writer  to  ascertain  the 
readiest  process  for  separating  mercury  from  the  ointment,  the 
three  following  methods  were  found  to  give  results  sufficiently 
accurate  for  the  Pharmaceutist. 
The  ointment  used  in  these  preliminary  experiments  was  care- 
fully prepared  by  himself  with  the  exact  proportions  of  the 
Pharmacopoeia. 
Uxp.  1.  A  portion  of  the  ointment  to  be  tested  is  put  in  a  test 
tube,  and  to  it  added  four  or  five  times  its  bulk  of  ordinary  hydro- 
chloric acid ;  the  whole  is  then  boiled  till  the  grease  entirely 
separates  and  floats  clear  on  the  surface,  an  operation  requiring 
but  a  few  moments ;  pour  off  the  liquid  portion,  being  careful 
not  to  lose  any  of  the  finely-divided  mercury.  Boil  the  residue 
once  or  twice  more  with  fresh  portions  of  the  same  acid,  until  the 
mercury  forms  a  globule ;  this  is  then  to  be  washed  with  water, 
dried  on  bibulous  paper  and  weighed. 
With  fifty  grains  of  the  ointment  treated  in  this  manner,  I 
obtained  twenty-four  grains  of  mercury. 
Exp.  2.  A  portion  of  the  ointment  is  introduced  into  a  test 
tube,  and  a  strong  solution  of  caustic  soda  added  :  these  are  boiled 
for  a  few  minutes,  and  then  allowed  to  stand,  that  all  the  black 
powder  may  settle ;  decant  the  liquid  portion,  and  wash  the 
residue  with  hot  water,  afterwards  boil  the  finely-divided  mer- 
cury with  some  hydrochloric  acid,  which  will  cause  it  to  run  into 
a  globule ;  this  should  then  be  washed,  dried  and  weighed. 
