Am.  Jour.  Pbarm.  ( 
October,  1911.  J 
Tincture  of  Cantharides. 
473 
potash  dissolved  in  water,  the  magma  heated  on  the  water-bath  to 
complete  the  reaction  and,  as  it  was  in  no  condition  to  percolate,  it 
was  dried  at  a  gentle  heat  and  ground.  It  could  then  be  percolated 
with  dilute  alcohol  and  yielded  a  tincture  assaying  0.106,  which 
practically  represented  the  full  strength  of  the  drug. 
This  tincture  was  compared  for  vesicating  power  with  a  U.S. P. 
tincture  assaying  about  one-third  as  much  cantharidin.  Three  drops 
of  the  U.S. P.  tincture  caused  distinct  redness  on  a  man's  arm 
and  six  drops  produced  vesication.  Three  drops  of  the  alkaline 
tincture  produced  no  visible  effect  and  six  drops  only  a  slight  redness. 
When  equal  volumes  were  evaporated  spontaneously,  a  few  drops  of 
acetic  acid  added  to  each,  and  then  mixed  with  a  definite  amount  of 
lead  plaster,  the  effects  were  about  equal  when  applied  to  a  shaven 
area  on  a  dog's  leg,  each  producing  redness  in  five  hours,  and 
vesicles  in  15  hours.  As  the  presence  of  lead  plaster  may  have 
prevented  to  a  considerable  extent  the  liberation  of  cantharidin,  this 
test  was  repeated,  using  lanolin  as  a  base.  The  result  did  not 
materially  differ  from  that  previously  obtained  even  when  the  test 
was  repeated  with  a  larger  amount  of  acetic  acid.  When  the  tincture 
itself  was  acidified  and  filtered  it  assayed  only  .062,  showing  a  loss 
of  40  per  cent,  of  cantharidin  which  in  all  probability  would  be 
still  greater  on  longer  standing.  As  acetone  is  a  much  better  solvent 
for  cantharidin  than  alcohol  a  tincture  was  made  by  exhausting  the 
drug  with  acetone,  recovering  the  solvent  and  dissolving  the  residue 
in  alcohol.  This  tincture  assayed  0.066  and  probably  contained  all 
the  free  cantharidin  in  the  drug.  It  is  a  question,  however,  whether 
this  amount  of  cantharidin  would  remain  permanently  in  solution  in 
an  alcoholic  tincture  and  as  there  can  be  no  serious  objection  to  the 
use  of  acetone  as  a  menstruum,  a  final  experiment  was  made  in  which 
the  cantharides  was  moistened  with  a  mixture  of  acetone  19  parts 
and  glacial  acetic  acid  i  part,  and  then  percolated  with  acetone. 
When  one-half  the  required  amoiint  of  tincture  had  been  obtained, 
the  percolate  was  almost  colorless  and  therefore  this  first  half  was 
assayed  separately  from  the  second  half.  A  second  fraction  equal 
in  volume  to  the  finished  tincture  was  also  obtained  and  assayed. 
The  results  were  as  follows : 
1st  half  of  tincture  =  0.140  ) 
2d  half  of  tincture  =  0.0078  f     average  —  0.0739 
Fraction  No.  2  =0.01 
