THE  PROCESS  OF  PERCOLATION. 
99 
a,  is  a  stand  for  the  receiving 
vessel.  Into  the  stand  is  secured, 
by  mortise  tenon  and  pin,  an  up- 
right of  2  by  4  inch  plank,  to  sup- 
port the  percolator.  On  the  upper 
end  of  this,  supported  by  what 
mechanics  call  an  o  g  bracket,  is 
a  small  shelf  or  platform  for  the 
menstruum  reservoir. 
5,  is  the  percolator,  supported 
upon  a  perforated  bracket  at  the 
lower  end,  and  attached  to  the  up- 
right support  at  the  upper  part  by 
a  strap  and  buckle,  e.  Into  the 
lower  opening  a  small  glass  stop- 
cock,/, is  fitted  by  means  of  a  per- 
forated cork.  This  stop-cock  may, 
without  inconvenience,  be  replaced 
by  two  short  pieces  of  glass  tube, 
and  an  inch  of  India-rubber  tubing 
of  corresponding  size.  One  piece 
of  the  glass  tube  is  fitted  to  the 
percolator  by  a  perforated  cork, 
at  one  of  its  ends.  The  India  rub- 
ber tube  is  then  stretched  over  the 
other  end  of  this  first  glass  tube, 
while  the  second  piece  of  glass 
tube  is  inserted  into  the  India-rubber  tube  below.  A  piece  of 
thread  being  then  tied  loosely  round  the  India  rubber  portion 
may  be  made  into  a  good  compression  stop-cock,  by  inserting  a 
little  wedge  of  wood  between  it  and  the  India-rubber  tube. 
The  farther  this  wedge  is  pushed  in,  the  more  it  contracts  the 
tube.  The  lower  piece  of  glass  tube  may  be  dispensed  with, 
but  the  contrivance  is  not  so  neat.  Where  this  tube  enters  the 
receiving  bottle,  it  should  be  tied  round  with  paper  or  muslin  to 
prevent  loss  by  evaporation. 
The  upper  end  of  the  percolator  should  be  tied  over  with  sheet 
India-rubber,  in  which  two  holes  have  been  made  for  the  tubes. 
d,  is  the  menstruum  reservoir,  large  enough  to  hold  an  entire 
