IMPROVED  PROCESS  FOR  FLUID  EXTRACT  OF  BUCHU.  131 
"  tinctures,''  while  the  word  percolate  would  appear  to  he  more 
accurate  as  well  as  more  appropriate. 
The  next  criticism  is  upon  the  more  important  points  of  the 
practical  application  of  the  process;  and  here  the  writer  feels 
much  more  within  his  own  legitimate  sphere.  "  Buchu  in  mode- 
rately fine  powder"  is  directed.  This  degree  of  fineness  is  de- 
fined, on  page  7,  as  being  obtained  by  a  sieve  of  fifty  meshes  to 
the  inch.  The  writer's  experience  indicates  that  a  much  finer 
powder  is  better  ;  that  the  ordinary  dusted  powder,  which  passes 
easily  through  a  sieve  of  one  hundred  and  twenty  meshes  to  the 
inch,  works  well  in  practice  on  any  scale  ;  and  that  it  is  impossi- 
ble to  have  the  powder  too  fine.  The  most  important  of  the 
cardinal  rules  which  apply  to  successful  percolation,  and  that 
upon  which  the  success  almost  entirely  depends,  is  the  rate  at 
which  the  percolate  passes,  and  this  cannot  be  well  controlled  in 
the  use  of  coarse  powders. 
In  the  use  of  the  Pharmacopoeia  quantities,  or  indeed  upon 
any  moderate  scale,  the  perQolate  should  pass  off  not  faster  than 
a  drop  in  each  second  at  first,  getting  a  little  faster  as  the  ex- 
haustion progresses.  The  most  successful  and  thorough  percola- 
tions are  the  slowest,  and  such  require  the  smallest  quantity  of 
menstruum  for  exhausting.  The  best  efforts  of  the  writer,  when 
operating  on  quantities  of  from  thirty  to  fifty  times  the  officinal 
formulas,  have  been  with  dusted  powders,  percolated  at  the  rate 
of  a  drop  for  every  three  seconds,  or  twenty  drops  a  minute, 
this  rate  being  obtained  of  course  through  the  fineness  of  the 
powder  as  well  as  by  the  packing. 
The  next  point  to  be  noticed  is  that  the  quantity  (two  pints) 
of  weak  percolate  directed  to  be  obtained  is  excessive  in  view  of 
the  present  cost  of  alcohol,  and  the  amount  of  medicinal  extract 
obtained  by  it.  The  s.  g.  of  the  alcohol  used  as  the  menstruum 
is  *835.  That  of  the  reserved  percolate  is  -914.  That  of  the  first 
of  the  two  pints  of  weak  percolate  is  *861.  And  that  of  the 
second  of  the  two  pints  is  "844.  This  two  pints  of  weak  percolate, 
when  evaporated  slowly  to  four  fluidounces,  has  a  specific  gravity 
of  1-049,  much  of  which  gravity  is  due  to  oxidation  during  the 
evaporation.  When  the  two  portions  are  mixed  together,  and 
before  the  filtration,  the  s.  g.  is  *953.    After  filtration  it  is  "946. 
