134  PREPARATION  Or  RESIN  OF  PODOPHYLLUM. 
ascertained  by  dropping  the  percolate  into  water,  when,  if  it 
contains  an  appreciable  portion  of  resin,  each  drop  will  occasion 
a  slight  cloudiness. 
2d.  Concentrating  the  tincture  In  large  operations  it  will 
be  desirable  to  recover  the  alcohol,  which  may  be  done  with  very 
little  trouble  with  a  pharmaceutical  still.  In  evaporating  a 
pint  or  two  of  the  tincture,  an  evaporating  dish  on  a  sand  bath, 
or  submitted  to  the  regulated  flame  of  a  gas  furnace,  will  serve 
a  good  purpose.  The  extent  of  the  evaporation  is  a  point  of 
importance,  to  determine  which  I  have  made  a  number  of  experi- 
ments. If  the  tincture  is  not  concentrated  enough,  a  consider- 
able proportion  of  the  resin  will  remain  in  solution  when  added 
to  water  ;  if  too  much,  it  will  not  mix  with  water  sufficiently  to 
produce  a  favorable  separation  of  the  resin  ;  in  the  case  of  a  re- 
cipe furnished  with  a  view  to  its  insertion  in  the  Pharmacopoeia, 
I  obtained  three-fourths  as  much  resin  on  the  partial  evaporation 
of  the  liquid  after  the  separation  of  the  first  precipitate,  as  was 
precipitated  on  the  original  admixture  with  water.  The  best 
point  at  which  to  arrest  the  evaporation  appears  to  be  at  from 
2J  to  3J-  fluid  ounces  of  the  evaporated  tincture  to  each  pound 
of  the  root  treated. 
2>d.  Precipitating  by  water.  — The  proportion  of  water  to 
which  the  evaporated  tincture  should  be  added  is  not  unimport- 
ant. I  think  four  parts  of  water  to  one,  is  perhaps  most 
desirable.  If  the  specimen  of  the  root  treated  was  highly 
resinous,  and  the  extraction  was  very  complete,  the  alcoholic 
fluid  extract  may  be  rather  thick  and  even  of  a  syrupy  consist- 
ence at  the  degree  of  concentration  above  indicated  ;  in  this 
case  it  is  better  to  add  it  to  the  water  while  hot  and  compara- 
tively fluid. 
4th.  Collecting  the  precipitate. — In  some  instances,  in  which 
this  process  has  been  varied  to  test  the  eligibility  of  certain 
modifications,  the  resin  has  been  so  imperfectly  precipitated  as 
in  part  to  pass  through  a  filter,  remaining  suspended  in  the 
filtrate  ;  in  others,  though  arrested  by  the  filtrate,  it  could  be  only 
partially  separated  after  drying ;  in  no  case  could  it  be  suc- 
cessfully collected  by  subsidence,  so  that  several  experiments  were 
made  to  find  the  best  method  of  collecting  it.  The  most  suc- 
cessful of  these  consisted  in  heating  the  whole  aqueous  liquid 
