556 
Process  of  Percolation. 
f  Am.  Jour.  Pharm. 
\     Dec.  1,  1874. 
tempted,  for  all  that  it  will  cost,  to  continue  the  percolation  until  I 
have  stronger  evidence  that  the  drug  is  exhausted. 
There  is  also  another  prominent  feature  in  the  officinal  process  for 
fluid  extracts,  of  which  I  desire  to  saj  a  word,  and  that  is  in  regard 
to  the  use  of  glycerin  in  nearly  all  these  formulae. 
I  have  had  much  experience  in  the  use  of  glycerin  in  practical 
pharmacy,  and  there  is  no  one  who  holds  a  higher  opinion  of  it  than 
I  do,  both  as  a  solvent  and  preservative  of  the  active  properties  of 
many  drugs  ;  but,  I  must  confess,  I  have  never  found  it  so  nearly  a 
universal  solvent  and  preservative  as  the  authors  of  the  formulae  for 
fluid  extracts  of  our  Pharmacopoeia  seem  to  have  discovered.  In 
reviewing  these  formulae,  I  am  led  to  believe  that  glycerin  must  pos- 
sess latent  qualities,  in  this  respect,  that  have  escaped  my  notice. 
Glycerin  is  certainly  an  agent  of  inestimable  value  in  pharmacy,  but 
I  do  not  approve  of  its  indiscriminate  use — and  especially  when  em 
ployed  as  a  menstruum — in  percolation  in  making  fluid  extracts,  when 
the  object  is  to  obtain  saturated  or  highly  concentrated  percolates. 
In  such  cases,  it  must  be  handled  with  judgment,  and  only  by  the 
hand  of  experience,  or  it  may  prove  a  very  dangerous  impediment  to 
success  rather  than  a  means  thereto.  In  the  formulae  for  fluid  ex- 
tracts in  our  Pharmacopoeia,  I  think  it  has  been  used  with  a  too  lavish 
hand.  There  are  some  of  these  formulae  from  which,  I  cannot  but 
believe,  it  would  have  been  better  to  omit  it. 
It  should  be  held  as  a  cardinal  principle,  that  glycerin  should 
never  form  a  part  of  any  menstruum  for  fluid  extracts,  unless  it  is 
known  to  be  a  better  solvent  for  the  active  properties  of  the  drug  to 
be  exhausted  than  either  alcohol  or  water,  or  these  two  combined,  for, 
by  reason  of  its  greater  density,  it  in  a  measure  blunts,  as  it  were, 
and  interferes  with  the  solvent  action  of  the  latter  liquids.  And, 
when  its  presence  is  necessary  as  a  solvent,  or  when  its  retention  in 
the  finished  product  is  desirable  or  necessary  as  a  preventive  against 
decomposition  or  deposit,  it  must  be  employed,  as  I  have  before  re- 
marked, with  judgment.  It  can  rarely,  in  any  case,  be  used  with 
advantage  in  greater  proportion  than  from  one-eighth  to  one-fourth 
of  the  balk  of  the  menstruum,  notwithstanding  its  wonderful  sol- 
vent power  over  rhubarb,  cinchona  and  wild  cherry  bark,  and  other 
articles  that  might  be  named.  Yet,  if  it  forms  just  a  little  too  large  a 
proportion  of  the  menstruum,  even  in  such  instances,  it  enfeebles  the 
action  of  the  menstruum  and  percolation  proceeds  in  an  unsatisfactory 
manner. 
