322 
ON  PERCOLATION  OR  DISPLACEMENT. 
porating  only  the  weaker.  This  brings  us  to  consider  the  sub- 
ject of  saturation  in  regard  to  pharmaceutical  menstruua,  and 
to  explain  how  it  is  that  a  solution  by  direct  displacement  is 
necessarily  more  concentrated  than  one  by  displacement  pre- 
ceded by  maceration  or  by  simple  macera  tion.  By  way  of  illus- 
tration, let  us  take  krameria :  1.  The  strongest  aqueous  solu- 
tion attainable  by  maceration  is  that  obtained  by  saturating 
rhatany  powder  with  water,  letting  it  stand  in  a  cool  place  for 
24  or  48  hours  and  then  expressing  it.  The  largest  proportion 
of  material  is  thus  brought  in  contact  with  the  smallest  propor- 
tion of  solvent  possible  in  this  method,  which  we  will  assume  to 
be  a  pound,  (7000  grs.)in  a  pint. 
2.  If  now,  instead  of  pressing  this  rhatany,  it  be  placed  in 
a  percolator  properly  packed,  and  treated  with  water,  so  as  to 
displace  the  infusion  very  slowly,  the  first  fluid  ounce  that 
passes  will  nearly  represent  the  liquid  by  maceration.  The 
second  fluid  ounce  will  be  stronger  by  the  amount  of  matter  dis- 
solved in  its  passage  through  the  powder  occupied  by  the  first 
fluid  ounce.  The  third  fluid  ounee  will  be  yet  denser,  owing  to 
its  gathering  up  from  the  leaving  of  the  first  and  second 
fluid  ounces.  And  this  goes  on  until  the  added  menstruum 
begins  to  mix  with  the  last  portions,  when  the  specific  gravity 
cf  the  mixture  will  be  less  than  that  of  the  infusion  originally 
absorbed. 
3.  But  when  you  operate  by  direct  displacement,  (or  in  the 
way  proposed  by  Prof.  Grahame,  which  amounts  to  nearly  the 
same  thing,  and  is  more  certain,)  the  first  fluid  ounce  of  liquid 
that  enters  the  powder  exerts  its  solvent  power  on  every  succes- 
sive layer  of  the  powder,  until  it  ceases  to  dissolve  any  more, 
after  which  it  is  simply  pushed  downward  by  the  gravity  of  the 
liquid  above,  minus  the  capillary  attraction  exerted  (sponge- 
like) by  the  powder  to  retain  it.  The  second  fluid  ounce  pro- 
ceeds in  like  manner  to  exert  its  solvent  power  till  saturated 
and  passed  ;  and  this  process  proceeds  so  long  as  the  amount  of 
soluble  matter  is  sufficient  to  wholly  satisfy  the  solvent  action 
of  the  water  during  its  contact,  after  which  point  the  liquids 
will  be  found  less  and  less  dense.  Now,  on  comparing  the  first 
portion  of  the  liquid  by  direct  displacement  with  the  others,  it 
will  be  found  to  be  much  stronger  and  more  syrupy  ;  and  though 
