AmMay"i^8arm'}     Fluid  Extracts  by  Rep er eolation.  237 
to  the  position  of  Fig.  3,  and  the  end  of  the  exit  tube  placed  in  the 
bottle  marked  for  the  reserved  percolate,  for  10  or  15  minutes,  in  order 
that  the  bubbles  of  air  may  be  driven  out  and  the  tube  be  filled  with 
solid  liquid.  As  soon  as  this  condition  is  attained  the  percolator  is 
lowered  to  the  position  of  Fig.  1,  and  the  receiving  bottle  is  then  to  be 
adjusted  higher  or  lower  until  a  rate  of  dropping  is  established  of  not 
more  than  one  drop  per  minute  on  this  small  scale, — and  one  drop  every 
two  minutes  makes  a  better  rate  for  such  quantities.  Indeed  the  rule 
for  all  percolations  is,  the  slower  the  rate  the  more  perfect  the 
exhaustion,  and  with  a  smaller  quantity  of  menstruum. 
This  slow  rate  and  the  automatic  supply  by  the  inverted  bottle  admit 
the  process  to  go  on  night  and  day,  but  if  it  be  desired  to  go  slower, 
that  a  mark  may  not  be  passed  in  the  night,  the  bottle  has  only  to  be 
raised  or  the  percolator  lowered  a  little  ;  and  by  a  still  greater  change 
of  levels  the  dropping  may  be  stopped  altogether.  On  rare  occasions 
when  dropping  at  a  uniform  rate  it  will  stop  altogether,  or  become  very 
slow.  This  is  in  consequence  of  a  bubble  of  air  getting  over  the  ori- 
fice of  the  glass  tube  inside,  and  acting  as  an  obstruction.  If  the  tube 
be  moved  from  side  to  side  the  air  bubble  will  be  started  and  pass  down 
and  the  rate  of  dropping  be  resumed.  If  not  thus  dislodged  it  will 
most  certainly  be  by  raising  the  percolator  for  a  short  time  into  the 
position  of  Fig.  3.  With  some  powders,  and  some  degrees  of  moist- 
ening and  packing  the  proper  rate  of  dropping  will  require  the  position 
of  Fig.  2,  and  in  some  stages  of  many  percolations  this  position 
will  be  required.  While  if  for  want  of  skill  and  experience  the  pack- 
ing be  too  hard  the  position  of  Fig.  3  may  be  needed  from  the  first. 
But  the  best  percolations  are  those  obtained  by  the  position  of  Fig.  1, 
where  the  whole  mass  is  in  the  equilibrium  of  maceration,  and  the  fluid 
all  moves  downward  together  at  a  very  slow  rate.  As  the  more  con- 
centrated portions  of  percolate  get  through,  the  rate  of  dropping  in- 
creases for  any  position,  and  occasionally,  with  loose  packing,  the  posi- 
tion has  to  be  altered  to  check  it.  But  after  the  reserved  portion  has 
been  received,  and  the  quantity  required  to  moisten  the  next  powder, 
the  rate  of  dropping  may  be  doubled  without  much  harm,  and  thus  half 
the  time  be  saved.  The  slow  and  uniform  rate  of  dropping  is  the  im- 
portant point  to  be  attained,  and  the  various  positions  are  simply  means 
of  accomplishing  this.  It  is  easy  to  obtain  complete  exhaustion.  That 
is,  a  percolate  almost  colorless  and  tasteless,  and  having  the  same  s.  g. 
