154  ON  THE  PREPARATION  OF  FLUID  EXTRACTS. 
is  a  proper  addition  in  the  preparation  of  simple  fluid  extracts 
of  these  substances. 
Mr.  Campbell,  after  moistening  the  drug  upon  which  he  is 
operating,  packs  it  in  a  percolator  and  allows  it  to  macerate 
therein  for  four  days,  after  which  he  proceeds  to  displace  the 
tincture.  By  this  process  the  portion  in  the  bottom  of  the  in- 
strument is  subjected  to  a  more  thorough  action  of  the  men- 
struum than  that  near  the  top,  and  while  the  lower  portion  would 
be  entirely  exhausted,  it  might  perhaps  be  doubted  whether  the 
upper  portion  was  eqlially  so,  although  long  maceration  seems 
entirely  to  loosen  the  soluble  from  the  insoluble  portion,  while 
percolation  merely  washes  out  the  soluble  part  so  separated. 
I  would  suggest  that  the  maceration  should  not  be  made  in  the 
percolator,  but  in  a  separate  vessel,  and  that  once  or  oftener 
during  the  maceration  it  would  be  advisable  to  thoroughly  stir 
the  mixture,  since  the  upper  part  would  naturally  become  dryer 
than  the  lower.  By  this  means  the  maceration  would  be  made 
more  uniform  throughout  the  mass,  while  at  the  same  time  there 
would  be  less  danger  of  the  menstruum  running  in  particular 
grooves  or  channels.  In  the  case  of  resinous  or  gummy  sub- 
stances, previous  to  percolation,  I  would  recommend  the  addi- 
tion of  sand,  washed  sawdust,  the  residue  of  a  previous  opera- 
tion, or  some  other  inert  substance,  whereby  a  freer  passage 
may  be  given  to  the  menstruum,  care  being  taken  to  have  the 
mixture  uniform,  and  the  packing  in  the  percolator  being  care- 
fully attended  to. 
Mr.  Campbell  recommends  the  use  of  glass  funnels  or  perco- 
lators in  all  cases,  and  it  is  probable  that  there  are  very  few  in- 
stances in  which  they  will  not  answer  a  good  purpose.  From 
the  experience  I  have  had,  however,  in  the  use  of  percolators  of 
various  shapes,  I  believe  that  the  best  form  of  percolator  is  the 
section  of  a  cone  having  about  the  following  proportions  :  its- 
length  should  be  twice  that  of  its  largest  diameter,  and  four 
times  that  of  its  smallest  diameter.  If  made  of  glass,  the 
smaller  end  should  terminate  in  a  rounded  funnel  with  a  short 
neck ;  if  made  of  tinned  iron,  an  ordinary  funnel  makes  a  very 
good  termination. 
In  view  of  the  great  simplicity  of  this  process,  and  the  ease 
