Amil™\wm'}      Fluid  Extracts  by  Repercolation.  235 
all  intermediate  positions  are  often  useful  and  necessary  even  in  the 
same  percolation.  The  support  is  a  common  apparatus  stand,  the 
rings  of  which  are  reduced  to  the  proper  size  by  short  sections  of  rub- 
ber-tubing cut  open  and  placed  on  the  wire  of  the  ring  when  needed  ; 
or,  a  section  of  larger  tubing  stretched  over  the  percolator  as  in  Fig.  3. 
The  percolators  are  common  lamp  chimnies  costing  about  5  cents  each, 
and  are  of  the  size  and  form  known  technically  as  "A"  and  "  B  " 
"  Sun  Chimneys."  These  are  of  very  good  form,  though  not  the  best, 
— for  percolators,  and  should  be  selected  with  as  small  an  opening  for 
the  stopper  as  possible,  and  with  the  smoothest,  thickest  and  most  reg- 
ular edge,  since  it  is  practically  impossible  to  stop  some  of  their  irreg- 
ular edges  tightly.  The  smaller  size,  Fig.  3,  holds  conveniently  4 
ounces  of  most  powders,  and  the  larger  holds  8  ounces, — to  the  points 
shown  in  the  cut.  A  good  soft  cork,  bored  in  the  centre  for  a  short 
piece  of  glass  tube  of  not  more  than  Jth  of  an  inch  or  3mm.  bore, 
serves  to  close  the  small  end  of  the  chimney.  A  rubber  cork  is  best, 
and  such  may  be  made  of  concentric  sections  of  rubber  tubing  of  dif- 
ferent sizes  ;  or,  the  largest  cork  at  hand  may  be  increased  to  the 
proper  size  by  stretching  around  it  short  sections  of  rubber  tubing. 
The  short  piece  of  glass  tubing  should  not  go  quite  through  the  cork 
on  the  inside,  and  should  project  about  an  inch=25mm.  outside.  A 
piece  of  rubber  tubing  of  not  over  |th  inch=3mm.  bore,  and  about  13. 
inches=*325m.  long  has  one  end  slipped  onto  the  glass  tube.  If  this 
tubing  be  much  larger  than  the  dimensions  given  it  fails  to  be  filled 
with  the  liquid,  and  then  when  the  percolator  is  in  the  position  of  Fig. 
3,  it  fails  to  perform  the  office  of  a  Sprengel  pump  in  exhausting  the 
liquid  and  air  bubbles  from  the  lower  part  of  the  percolator.  Two. 
disks  of  blanket  or  thick  flannel,  and  one  of  filtering  paper  cut  a  little 
larger  than  the  inner  surface  of  the  cork,  and  laid  upon  it,  complete 
the  arrangement  of  the  percolator.  The  powder,  moistened  with  great 
care  and  uniformity  is  packed  loosely,  firmly  or  very  firmly,  according 
to  its  nature  or  condition,  with  the  square  end  of  a  stick,  say  -8  inch 
—•02m.  diameter.  As  a  rule  the  largest  practicable  proportion  of 
liquid  should  be  used  in  moistening  the  powder,  because  then  the  pow- 
der occupies  the  smallest  space  in  the  percolator, — requires  the  loosest 
packing,  and  is  saturated  for  the  maceration  by  the  smallest  additional 
quantity  of  liquid,  and  therefore  gives  the  most  concentrated  first  per- 
colate for  the  reserve,  and  secures  the  most  rapid  exhaustion  by  the 
