98 
THE  PROCESS  OF  PERCOLATION. 
stand  in  a  covered  vessel  for  twelve  hours  before  being  put 
into  the  percolator. 
The  percolator  should  have  a  heighth  equal  to  four  times  its 
diameter,  at  least,  and  should  be  furnished  at  the  lower  end  with 
a  stop-cock,  or  India-rubber  tube,  by  which  to  regulate  the  rate 
of  percolation.  Upon  the  perforated  diaphragm  of  the  lower 
part  should  be  placed  two  disks  of  flannel,  with  a  disk  of  filter- 
ing paper  between  them. 
The  wetted  substance  should  be  put  into  the  percolator  com- 
pactly, but  not  tightly,  so  as  to  occupy  about  five-sixths  of  the 
capacity  of  the  percolator,  and  be  covered  by  a  disk  of  flannel 
tucked  down  round  the  edges. 
There  should  be  a  stratum  of  menstruum  kept  upon  the  sub- 
stance in  the  percolator,  until  the  whole  of  the  prescribed  quan- 
tity of  liquid  has  been  added. 
The  rate  of  percolation  should  be  so  controlled  that  in  perco- 
lating one  pound  of  substance  the  percolate  should  drop  into  the 
receiver  at  the  rate  of  one  drop  every  two  seconds,  or  about 
3  f.I  per  hour  ;  and  for  larger  quantities  in  the  same  ratio. 
The  first  and  last  of  these  simple  rules  are  most  important, 
and  if  carefully  observed  will  furnish  good  and  equable  prepara- 
tions. The  controlling  the  rate  of  percolation  proved  to  be  so 
important  to  the  process,  that  the  writer  very  soon  abandoned 
the  attempt  to  do  this  by  the  mere  packing  of  the  substance  in 
the  percolator ;  whilst  the  alternative  adopted  for  the  purpose 
in  a  great  measure  obviates  the  necessity  for  the  skill  and  judg- 
ment necessary  in  manipulating  each  particular  drug.  The 
most  common  faults  in  percolation  are  in  having  the  substances 
too  coarsely  powdered,  and  in  percolating  too  rapidly. 
By  attention  to  the  rules  above  given,  and  by  the  adaptation 
of  a  few  little  simple  contrivances,  (which  any  one  can  make  for 
himself,)  such  as  are  shown  in  the  adjoining  sketches,  the  process 
has  become  in  the  writer's  hands  so  convenient,  easy,  and  so 
automatic,  that  it  has  ceased  to  require  or  attract  any  particular 
attention. 
Figure  1  is  a  centre  section  sketch  of  an  automatic  percolator, 
which  the  writer  has  for  some  time  had  in  use,  drawn  on  a  scale 
of  half  an  inch  to  the  foot. 
