AmMa°y,ri8>7h8arm'}      Fluid  'Extracts  by  Rep  er  eolation.  243 
the  crucial  cut  are  reflected  up  against  the  outside  of  the  tube.  These 
corners  are  then  tied  firmly  to  the  tube  by  passing  twine  around  them, 
or,  are  secured  by  a  stout  rubber  band,  g,  made  of  a  section  of  rubber 
tubing  of  proper  size.  A  disk  of  filtering  paper,  d,  larger  than  the 
upper  blanket,  c,  with  a  crucial  cut  in  the  centre,  and  nicked  round  the 
edge  so  as  to  lie  flat  against  the  sides  of  the  percolator  where  reflected 
up  against  them.  This  disk  of  paper  is  pushed  down  upon  the  upper 
blanket,  the  well-tube  passing  through  the  crucial  cut  in  its  centre. 
If  now  a  piece  of  paper  be  twisted  round  the  upper  end  of  the  well- 
tube,  or  a  cork  be  temporarily  stuck  into  it,  to  keep  out  the  moistened 
powder,  the  percolator  is  ready  to  receive  its  charge  which  is  packed 
around  the  well-tube  and  upon  the  disks  of  paper  and  blanket  so  as  to 
occupy  the  main  body  of  the  percolator,  h,  up  to  about  the  position 
ofi. 
When  the  charge,  having  been  properly  moistened,  rubbed,  and 
sifted,  so  as  to  be  entirely  uniform  and  free  from  wet  lumps,  is  packed 
around  the  well  tube  loosely  or  firmly  according  to  the  nature  of  the 
substance  and  the  menstruum, — its  surface  is  covered  by  a  disk  of 
muslin  or  paper,  z,  cut  so  as  to  lie  flat  and  smoothly  upon  the  surface. 
The  object  of  this  is  to  distribute  the  menstruum  as  it  is  poured  on, 
and  to  prevent  the  stream  from  breaking  up  and  deranging  the  surface. 
Should  this  disk  show  a  tendency  to  float  in  the  stratum  of  menstruum 
it  may  be  weighted  down  by  a  few  fragments  of  glass.  The  percola- 
tor is  then  ready  to  receive  the  menstruum  or  weak  percolate,  and  a 
stratum  of  the  liquid  should  be  carefully  kept  covering  the  entire  sur- 
face well  until  the  whole  mass  of  the  substance  to  be  percolated  is 
entirely  saturated.  The  cork  is  to  be  taken  from  the  well- tube  before 
the  liquid  is  poured  on,  and  then  the  liquid  will  pass  down  into  the 
substance  like  a  piston,  pushing  the  interstitial  air  down  before  it  to 
pass  out  through  the  blankets  and  the  well  tube  ;  and  finally  the  liquid 
will  rise  in  the  well-tube  until  its  surface  is  within  an  inch  or  so  of  the 
surface  of  the  liquid  outside. 
The  whole  substance  is  now  in  a  perfect  condition  for  maceration, 
and  the  surface  should  be  left  covered  with  the  liquid  to  the  depth  of 
at  least  '\  inch  =  1  centimetre.  In  the  larger  percolator  a  short  sec- 
tion of  rubber  tubing,  0,  is  stretched  over  the  upper  end  of  the  well- 
tube,  and  slipped  down  so  as  to  support  the  centre  of  the  cover.  A 
tightly  fitting  cover,  /,  made  of  sheet  rubber  "25  inch  =  6  millimetres 
