196         TINCTURE  AND  FERRATED  TINCTURE  OF  BARK. 
given  menstruum,  because  of  our  inability  to  break  up  each 
individual  cell.  While  I  recognize  this,  I  believe  the  cause 
of  the  incomplete  exhaustion,  in  the  above  instance,  to  lie  in  a 
different  direction,  namely  in  the  natural  condition  of  the 
alkaloids  in  the  bark,  which  are  there  partly  combined  with 
with  kinic,  cinchotannic  and  probably  also,  at  least  in  some 
species,  with  rufo-cinchotannic  acid.  This  fact  will  point  out 
directly  the  necessity  of  employing  for  our  tinctures  a  stronger 
alcohol. 
Simple  tinctures  made  from  red  or  Galisaya  bark  with  diluted 
alcohol,  often  commence  to  precipitate  before  the  percolation  is 
finished,  or  at  least  in  the  course  of  a  few  days.  A  tincture, 
however,  prepared  by  percolation  with  alcohol,  of  '811  spec, 
grav.  (3  fluid  parts  alcohol  of  -835  and  1  p.  water,)  retains  every 
constituent  in  solution,  though  it  ma?/,  perhaps,  ultimately  pro- 
duce some  precipitate,  and  the  bark,  after  exhaustion,  does  not 
yield  any  alkaloids  to  a  stronger  alcohol.  The  rational  solvent, 
therefore,  for  our  officinal  tinctures  is,  not  diluted  alcohol,  but  a 
mixture  of  1  part  of  water  with  3  parts  of  alcohol,  or  perhaps 
still  better,  oflicinal  alcohol. 
We  must  keep  in  mind  that  by  employing  a  stronger  alcoholic 
menstruum,  changes  by  oxidation  are  by  no  means  prevented, 
but  on  the  contrary  rather  facilitated,  as  I  attempted  to  prove 
two  years  ago,  in  a  paper  on  the  preservation  of  fluid  extracts. 
To  the  doctrines  laid  down  in  that  paper,  I  still  adhere  j  not- 
withstanding this,  I  now  recommend  a  menstruum  for  the 
tinctures  of  bark,  stronger  in  alcohol,  for  the  following  reasons : 
The  principal  constituents  of  bark,  the  alkaloids,  are  not 
likely  to  be  easily  affected  by  the  exposure  to  the  air  in  the 
presence  of  alcohol  ;  at  least  not  if  heat  is  avoided  as  much  as 
possible.  I  have  isolated  quinia  from  tinctures  and  their  pre- 
cipitates several  years  old.  I  have  also  observed  kinic  acid  in 
the  tincture,  and  as  I  have  shown  above,  in  old  precipitates 
from  ferrated  tincture  of  bark  ;  kinic  acid,  for  this  reason  does 
not  appear  to  be  prone  to  change  by  exposures.  Rufo-cincho- 
tannic acid,  however,  as  has  been  shown  by  many  chemists, 
increases  in  quantity  with  the  age  of  the  solution,  while  the 
cinchotannic  acid  gradually  disappears  ;  the  medicinal  effects  of 
this  product  of  decomposition,  if  we  mny  judge  from  analogy 
