252         ON  THE  PREPARATION  OP  MEDICAL  TINCTURES. 
ing  this  deposit  was  inert,  and  that  its  preparation  did  not  lessen 
the  value  of  the  medicine.  It  would  be  quite  the  reverse  were 
this  deposit  formed  essentially  of  principles  possessing  great 
activity.  This,  then,  is  a  point  which  it  was  necessary  should  be 
cleared  up  by  a  series  of  consistent  researches  and  qualitative 
analysis,  executed  with  all  possible  care  and  precision. 
It  is  important,  also,  in  estimating  the  value  of  the  tinctures, 
not  to  rely  solely  on  their  relative  densities,  or  on  the  quantity 
of  dry  residue  left  by  evaporation,  but  rather  on  the  results  of 
the  analyses  of  these  residues,  for  it  sometimes  happens  that 
the  best  tincture  gives  the  least  residue,  being  richer  in  alkaloids 
and  other  really  active  principles  than  those  giving  the  smaller 
quantity  of  residue.  I  am  aware  that  the  researches  I  have 
indicated  would  require  much  time  and  skill  on  the  part  of  the 
operator,  but  there  are  many  druggists  capable  of  successfully 
undertaking  them. 
One  word  more  concerning  tinctures. 
In  my  opinion,  alcohol  is  not  so  good  a  preservative  as  it  is 
generally  supposed  to  be,  and  the  tinctures  should  be  used  as 
soon  as  possible  after  they  are  prepared.  The  following  facts 
pr"ove  that  certain  immediate  principles  of  vegetable  origin  alter 
when  dissolved  in  alcohol. 
A  tincture  prepared  from  the  leaves  of  a  plant  will  be  of  a 
beautiful  green  color,  due  to  the  presence  of  chlorophyl,  and 
will,  under  the  influence  of  hydro-chloric  acid,  undergo  trans- 
formations, which  M.  Fremy  has  described,  and  which  I  have 
studied  myself.  .Now,  these  transformations  do  not  take  place 
in  a  tincture  which  has  been  prepared  for  several  months,  and 
the  most  essential  characteristics  of  chlorophyl  disappear. 
The  petals  of  the  ranunculus,  macerated  in  alcohol,  give  a 
golden  yellow  tincture,  which,  on  the  addition  of  an  equal  volume 
of  hydrochloric  acid,  turns  green.  After  the  liquid  has  been 
filtered,  a  yellow  substance  remains  on  the  paper,  and  the  filtered 
liquid  is  of  a  pure  blue  colour.  Nothing  of  this  kind  takes  place 
when  the  tincture  has  been  kept  some  time.  Then  the  liquid 
remains  yellow  in  spite  of  the  addition  of  hydroeholoric  acid. 
In  this  case  the  xanthine  of  the  flowers  has  been  altered,  as  well 
•  as  the  chlorophyl. 
