472 
Tiyicture  of  Cantharides. 
(  Am.  Jour.  Pli&rm. 
\     October,  1911. 
tincture  assayed  0.031.  Hot  percolation  was  employed  on  another 
lot,  stopping  when  the  correct  amount  of  tincture  was  obtained. 
This  assayed  0.035.  The  drug  was  thereupon  further  percolated,  the 
weak  percolate  reduced  to  small  volume  under  reduced  pressure 
and  incorporated  with  the  first  percolate  which  then  assayed  0.0499. 
The  small  amount  of  light-colored  sediment  which  forms  in  these 
tinctures,  on  standing,  contains  cantharidin  which  may  be  ammonium 
cantharidate  or  some  similar  combination,  as  it  is  quite  likely  that 
ammonia  or  an  amine  is  formed  when  the  drug  is  subjected  to  heat 
or  by  aging.  A  small  experimental  lot  was  now  made,  using  hot 
percolation  and  obtaining  four  successive  fractions  each  equal  in 
volume  to  the  amount  of  tincture  to  be  finished.  These  assayed  as 
follows : 
No.  I — .058  No.  3 — .003 
No.  2 — .010  No.  4 — .002 
It  is  evident  that  the  first  two  fractions  contain  practically  all 
the  cantharidin  that  can  be  obtained  in  this  way.  This,  however, 
is  only  about  two-thirds  of  what  was  in  the  drug  and  the  question 
arises,  why  were  the  succeeding  fractions  so  weak?  The  solution 
probably  lies  in  the  condition  indicated  above,  that  part  of  the  can- 
tharidin is  present  as  a  cantharidate  which  is  but  very  sparingly 
soluble  in  alcohol.  From  this,  it  seems  imperative  that  some  acid 
be  used  if  alcohol  is  to  be  the  extracting  agent  or  if,  as  later  results 
show  to  be  desirable,  the  cantharidin  is  wanted  in  the  uncombined 
state.  However,  a  better  solvent  than  alcohol  is  needed  to  make  a 
full-strength  tincture  even  though  acid  is  used.  This  is  shown 
by  the  fact  that  when  the  drug  was  moistened  with  a  mixture  of 
equal  parts  glacial  acetic  acid  and  alcohol,  allowed  to  stand  several 
hours  and  then  percolated  with  alcohol,  the  resulting  tincture  assayed 
only  .04. 
The  plan  of  converting  all  the  cantharidin  into  cantharidate  was 
next  tried  and  a  portion  of  drug  was  mixed  with  magnesium  oxide, 
moistened  with  water  and  dried  at  a  gentle  heat.  It  was  then 
divided,  one-half  being  percolated  with  alcohol  and  the  other  half 
with  dilute  alcohol.  The  resulting  tinctures  assayed :  alcohol  .023 
and  dilute  alcohol  0.053,  showing  that  the  weaker  menstruum  is 
much  the  better  for  combined  cantharidin.  Using  a  caustic  alkali, 
it  was  found  necessary  to  add  considerable  excess  as  the  fat 
present  in  the  drug  requires  a  certain  amount  for  saponification.  A 
quantity  of  drug  was  moistened  with  one-tenth  its  weight  of  caustic 
