236  Fluid  Extracts  by  Reper  eolation.      { '^i^igt"* 
smallest  quantity  of  liquid.  A  disk  of  filtering  paper  is  placed  on  the 
surface  of  the  powder,  of  such  size  that  the  edge  is  reflected  up  against 
the  glass.  A  disk  of  board,  card-board,  or  better  of  thick  sheet  rub- 
ber with  a  central  hole  1*5  inches='037m.  in  diameter,  is  used  for  a 
cover.  A  stratum  of  liquid,  maintained  at  a  uniform  thickness  of  '25 
inch=foo6m.  should  cover  the  powder  from  first  to  last,  so  that  it  may 
not  drain  and  contract,  or  admit  air  ;  and  this  is  best  maintained  by  an 
inverted  bottle  of  the  supply  liquid,  as  shown  in  the  cut.  The  length 
of  the  neck  and  mouth  of  such  bottle  may  be  conveniently  elongated 
when  needed  so  as  to  regulate  the  depth  of  the  stratum  of  liquid  above 
the  powder,  by  stretching  over  it  a  short  section  of  rubber  tubing  in 
the  manner  shown  in  the  first  group  of  the  cut,  Fig.  1.  When 
the  percolator  is  charged  and  ready  for  maceration  the  small  rubber 
tube  is  turned  up  and  fastened  with  a  piece  of  thread  or  rubber  band  so 
that  the  end  is  considerably  above  the  level  of  the  liquid  in  the  perco- 
lator, and  in  so  adjusting  it  care  must  be  taken  not  to  close  the  tube, 
because  as  the  liquid  decends  through  the  powder  to  fill  up  all  the  inter- 
stices it  is  important  that  the  interstitial  air  should  have  a  free  exit  by 
the  tube. 
The  bottles  for  receiving  the  percolate  are  common  round-shouldered 
prescription  bottles,  40Z.  for  the  small  percolator,  8oz.  for  the  larger. 
A  strip  of  paper  should  be  pasted  lengthwise  of  the  bottle,  and  at  the 
lower  end  of  this  the  tare  should  be  marked.  It  should  then  be  grad- 
uated to  the  quantities  desired  by  weighing  into  it  the  proper  quantity 
of  water  and  marking  at  each  level  if  more  than  one  be  desired.  This 
graduation  simply  serves  as  a  reminder  to  know  when  to  try  the  bottle 
on  the  scale,  for  whether  the  finished  fluid  extract  be  adjusted  weight 
for  weight,  or  by  an  arbitrary  weight  in  each  case  so  as  to  get  the 
relation  of  minim  for  grain,  this  must  equally  be  done  by  weighing. 
It  is  convenient  to  have  6  to  10  of  such  bottles,  and  then  as  soon  as 
4  are  filled  from  one  percolation  another  can  be  started,  and  thus  relieve 
some  of  the  bottles  for  use  over  again.  The  bottles  should  be  num- 
bered from  1  to  10  to  keep  the  proper  order  of  using  them,  and  if  more 
than  one  series  is  in  use  at  the  same  time  the  second  should  be  desig- 
nated by  the  first  letters  of  the  alphabet  instead  of  by  numbers.  The 
maceration  should  never  be  less  than  48  hours  ;  and  a  longer  time  does 
mot  seem  to  be  of  any  use  unless  the  powder  be  coarse  and  of  hard 
particles.    When  the  percolation  is  to  be  started  the  percolator  is  raised 
