294 
PHARMACY  OF  THE  CINCHONAS. 
should  not  be  picked  out,  or  even  taken  at  random,  for  this 
assay,  since  it  is  so  difficult  if  not  impossible  to  get  a  fair  average 
of  a  larger  lot  in  that  way.  But  rather  the  quantity  required 
for  the  stock  of  the  pharmacist  should  be  bought  subject  to  ap- 
proval, or  subject  to  a  verification  of  the  statements  made  as  to 
quality  by  the  seller  of  it,  and  then  if  unpowdered  the  whole 
should  be  powdered  and  sifted  together,  and  a  portion  of  the  well 
mixed  powder  be  then  taken  for  the  assay.  One  thousand  grains 
of  the  powder  is  weighed  upon  a  counterbalanced  paper,  and 
poured  into  the  largest  dish,  and  enough  alcohol  stirred  into  it 
to  wet  it  thoroughly  and  uniformly  into  a  smooth  even  magma  of 
almost  a  semifluid  consistence.  It  should  hardly  be  thin  enough 
to  pour,  but  just  thick  enough  to  be  transferred  with  the  end  of  a 
spatula  ,  without  running  off  or  dripping.  If  the  powder  be  very 
fine  and  dense  2  J  fluidounces  of  alcohol  will  be  sufficient.  If  a 
little  coarser,  or  lighter,  as  is  commonly  the  case  with  true  good 
Calisaya,  3  fluidounces  will  be  required.  Then  place  the  funnel 
in  the  marked  flask,  and  fold  two  three-inch  round  filters  into 
quarters,  in  the  usual  way,  by  twice  doubling  down  the  sheet. 
When  a  filter,  so  folded  in  the  common  way,  is  placed  in  a  fun- 
nel for#the  reception  of  the  substance,  there  are  three  thicknesses 
of  the  paper  against  one  side  of  the  funnel,  and  but  a  single 
thickness  against  the  other,  and  then  as  the  porous  paper  is  the 
only  channel  through  which  the  liquid  can  reach  the  receptacle 
below,  it  follows  that  the  three  thicknesses  of  paper  will  filter 
much  more  rapidly,  or,  under  some  other  circumstances,  much 
less  rapidly,  than  the  one  thickness.  Such  inequality  in  the  two 
sides  is  not  well  adapted  to  percolation ;  nor  should  a  ribbed 
funnel  ever  be  used  for  percolation,  nor  a  smooth  one  for  simple 
filtration,  if  it  can  be  avoided.  To  compensate  this  inequality  of 
sides  in  this  process,  let  the  one  little  folded  filter  be  placed 
inside  of  the  other,  with  the  three-thickness  side  of  one  applied 
to  the  single-thickness  side  of  the  other,  and  when  they  are  then 
placed  in  the  funnel  there  will  be  four  thicknesses  of  paper  ap- 
plied to  the  funnel  all  round,  thus  giving  a  uniform  direction  to 
the  passage  of  liquid  under  a  uniform  pressure  from  within. 
Such  details  are  often  of  more  importance  than  they  appear  to 
be,  and  are  easily  learned.    When  the  little  filters  are  thus  pro- 
