Am.  Jour.  Pharm. ) 
October,  1911.  j 
Tincture  of  Cantharides. 
471 
n/io  AgNOg.  Subtracting  this  from  the  corresponding  equivalent 
of  the  total  KCN  added,  multiplying  the  difference  by  0.3,  and  divid- 
ing this  product  by  the  weight  of  the  sample  taken,  the  quotient  will 
represent  the  percentage  by  weight  of  absolute  formaldehyde  in  the 
sample. 
TINCTURE  OF  CANTHARIDES.^ 
By  E.  G.  Eberhardt,  Indianapolis,  Ind. 
About  two  years  ago  when  an  attempt  was  made  to  prepare  a 
standardized  fluid  extract  of  cantharides,  it  was  discovered  that 
such  a  preparation  was  an  impossibility  because  of  the  sparing 
solubility  of  cantharidin  in  alcohol,  the  latter  being  considered  the 
only  proper  solvent.  When  the  investigation  was  extended  to  the 
tincture  it  was  found  that,  for  the  same  reason,  a  tincture  could  not 
be  made  which  represented  10  per  cent,  of  drug.  The  latter,  if  of 
good  quality,  will  average  about  i  per  cent,  of  cantharidin,  but  the 
tincture  made  by  the  official  method  only  assays  from  0.03  per  cent, 
to  0.04  per  cent.  This  same  fact  was  brought  out  in  a  paper  on 
"  Tincture  Cantharides,"  by  Prof.  W.  L.  Scoville,  read  at  the  1910 
meeting  of  the  American  Pharmaceutical  Association  and  he  there 
recommends  a  menstruum  of  alcohol  15  volumes  and  glacial  acetic 
acid  I  volume  as  giving  a  much  better  tincture,  the  results  averaging 
from  0.057  per  cent,  to  0.064  per  cent.  Prof.  Scoville  also  determined 
the  solubility  of  cantharidin  in  official  alcohol  at  25°  C.  to  be  i  :  1333 
(W.V.).  Accordingly  it  would  be  possible  to  have  a  tincture  made 
with  alcohol  assaying  .075  per  cent,  unless  the  accompanying  extract- 
ive would  decrease  the  solvent  power  of  the  menstruum  for  can- 
tharidin. 
As  complete  extraction  of  cantharides  could  not  be  accom- 
plished with  alcohol  at  the  ordinary  temperature  an  attempt  was 
made  to  obtain  an  alcoholic  prej^aration  of  maximum  strength 
by  the  use  of  heat.  A  lot  of  tincture  was  made  by  digesting  the  drug 
in  a  closed  vessel  with  hot  alcohol  for  about  two  hours,  allowing 
to  cool  at  room  temperature,  draining  off  the  liquid,  digesting  the 
residue  with  a  fresh  portion  of  alcohol  and  washing  the  residue 
finally  with  sufficient  alcohol  to  make  the  required  amount.  This 
^  Presented  before  the  Division  of  Pharmaceutical  Chemistry  at  the  In- 
dianapolis meeting  of  the  American  Chemical  Society,  Jnly,  tqti. 
