156    ON  THE  UNCERTAINTY  OF  PHARMACEUTICAL  PREPARATIONS. 
hol  two  pints  ;  macerate  for  fourteen  days,  express  and  filter  through 
paper.  Now  two  and  a  half  ounces  troy  or  apothecary's  weight 
are  1200  grains. 
Two  and  a  half  ounces  avoirdupois  are  1093|  grains. 
Making  a  difference  of  106J  grains. 
But  as  ordinarily  prepared  this  is  not  all  the  difficulty.  It  will 
be  observed  that  powdered  Opium  is  directed.  Opium,  in  drying, 
so  as  to  admit  of  its  being  powdered,  will  lose,  on  an  average, 
one-third  of  its  weight ;  therefore,  in  using  the  moist  gum  in  the 
preparation  of  the  tincture  only  740  grains  will  be  employed, 
which  is  but  a  little  over  one-half  of  the  requisite  quantity.  The 
object  of  having  the  Opium  powdered  is  to  insure  a  greater  uni- 
formity in  the  strength  of  the  tincture,  and  to  be  more  readily  acted 
upon  by  the  menstruum,  than  if  permitted  to  remain  in  hard  dry 
masses. 
We  will  now  cite  an  instance  of  a  different  character,  viz  :  the 
preparation  of  Mercurial  Ointment.    The  directions  are, 
Take  of  Mercury  two  pounds, 
"  Lard  twenty-three  ounces, 
"  Suet  one  ounce. 
Rub  the  mercury  with  the  suet  and  a  small  portion  of  the  lard 
until  the  globules  disappear,  then  add  the  remainder  of  the  lard  and 
mix. 
Two  pounds  apothecaries  weight  are  11520  grains. 
twenty-three  ounces  apothecaries  weight  are  11040  )  _ 
one  «  "  «  480  5  I101U  grS* 
That  is,  equal  weights  of  fat  and  mercury. 
Two  pounds  avoirdupois  weight  are  14000  grains, 
twenty-three  ounces  do.  10062J  )  menn 
,  .0^1  }  10500  grs. 
one  do.    do.  437i  )  6 
Which  shows  an  excess  of  3500  grains,  or  half  a  pound  avoir- 
dupois weight,  of  Mercury. 
These  two  instances  should  be  sufficient  to  satisfy  any  person  of 
the  importance  of  strictly  adhering  to  the  prescribed  rule. 
As  regards  the  administration  of  medicines:  For  the  last  few 
years  the  pharmaceutist  and  physician  have  been  laboring  to  con- 
centrate medicines,  and  at  the  same  time  to  render  the  various 
