238 
A  JVetr  Displacement  Apparatu.<i. 
/  Am.  Jour.  Pharm. 
I      May,  1882. 
displace!'  to  cover  the  drug.  The  .st()])-cock  M  is  then  closed  and  the 
materials  allowed  to  macerate  for  several  days. 
In  order  to  start  percolation,  the  receiver  C  is  exhausted  of  air  and 
the  taj)  i  having  been  opened  the  saturated  fluid  will  begin  drop])ing, 
and  continue  to  do  so,  so  long  as  the  force  of  the  vacuum  in  the 
receiver  is  equal  or  greater  to  that  in  the  up])er  vessel.  When  it 
begins  to  stop,  air  is  admitted  above  the  drug  which  is  drawn  through 
the  material,  carrying  with  it  much  of  the  remaining  liquid.  To  finish 
the  operation  air  is  forced  into  the  percolator  by  means  of  the  pump. 
Messrs.  Smith,  Kline  &  Co.,  of  this  city,  who  have  adopted  this 
apparatus  for  making  fluid  extracts,  state  that  they  find  it  works  very 
satisfactorily  and  economically  as  so  large  a  proportion  of  the  men- 
struum used  is  recovered.  As  an  instance  in  making  fluid  extract  of 
Wild  Cherry,  when  80  pounds  of  the  bark  are  used  80  pints  only  of 
liquid  are  employed  and  at  least  75  pints  are  recovered. 
From  what  is  here  stated  it  will  be  apparent  that  the  superiority  of 
this  mode  of  extraction  of  those  active  ingredients,  that  the  fluid 
extracts  and  tinctures  should  contain,  depends  chiefly  upon  two  condi- 
tions to  which  the  drug  operated  upon  is  subjected,  namely,  upon  the 
effect  produced  by  withdrawing  the  ordinary  pressure  of  the  atmos- 
23here,  not  only  on  the  surface  of  the  material,  but  on  each  particle  of 
the  substance ;  a  vacuum  being  thereby  produced  in  each  individual 
cell  which  is  at  once  filled  up  upon  contact  with  the  liquid  when  it  is 
admitted  into  the  vessel,  the  menstruum  under  these  conditions  being 
enabled  to  penetrate  much  more  quickly  and  readily  the  interior  of 
each  granule  of  the  article  operated  upon. 
The  advantage  of  the  other  condition  consists  of  exclusion  of  air, 
by  means  of  the  cover  and  retention  of  vapor  of  the  fluids  used  in 
making  the  preparations,  preventing  thereby  changes  which  might 
otherwise  occur,  both  in  the  liquid  and  solid  contents  of  the  percolator. 
As  only  such  drugs  are  used  that  have  been  well  dried,  we  can 
understand  readily  the  difficulty  with  which  many  of  them  are 
exhausted  by  the  usual  process,  when  we  take  into  consideration  that 
each  particle  of  the  drug  is  composed  of  cells  which,  by  desiccation, 
become  partially  empty,  offering  a  certain  amount  of  resistance  to  the 
entrance  of  liquids  in  somewhat  the  same  manner  that  a  piece  of 
pumice-stone  or  pith  of  sassafras  resist  the  penetration  of  water  when 
thrown  into  it.  Therefore,  if  a  vacuum  can  be  formed  in  these  cells, 
fluids  will  much  more  readily  surround  and  penetrate  them. 
