Am.    Jour.  Pharm.) 
March,  1920.) 
Cantharides  Assay, 
159 
The  assays  were  run  on  two  different  lots  of  cantharides  used  in 
our  manufacturing  department. 
First  Lot: 
U.  S.  P.  Method   0.71%  free  and  combined  cantharidin 
Author's  Method   i-i7%  free  cantharidin 
Second  Lot: 
U.  S.  P.  Method   (a)  0.569%  free  and  combined  cantharidin 
{h)  0.570%  free  and  combined  cantharidin 
Author's  Method   (a)  0.795%  free  cantharidin 
{h)  0.810%  free  cantharidin 
Baudin's  Method   {a)  0.789%  free  cantharidin 
(&)  0.753%  free  cantharidin 
Author's  Method  Modified          {a)  1.73%  free  and  combined  cantharidin 
(b)  1.11%  free  and  combined  cantharidin 
The  method  pursued  in  this  laboratory  is  the  one  given  here  under 
the  heading  "Author's  Method."  It  is  the  assay  method  of  Baudin 
as  given  in  Hager's  "Handbuch  der  Pharmaceutischen  Praxis,"  Vol.  i,; 
page  595,  and  in  Sadtler  and  Coblentz's  "Pharmaceutical  and  Medi- 
cal Chemistry,"  Vol.  2,  page  226,  modified  only  so  as  to  make  it  a 
complete  extraction  method,  instead  of  an  aliquot  portion  method. 
We  have  nothing  now  to  suggest  as  to  the  relative  value  of  these  two 
well-known  chemical  procedures  except  to  express  a  preference  for 
total  extraction  methods.  This  does  not  seem  to  agree  with  the 
trend  of  development  of  the  U.  S.  P.  text. 
A  glance  at  the  U.  S.  P.  will  leave  no  doubt  that  the  cantharides 
assay  is  a  very  troublesome  and  difficult  procedure.  Note  the  di- 
gestion, maintained  at  40°  C.  for  three  hours  with  frequent  shaking. 
Note  the  evaporation  to  about  5  Mils,  and  the  addition  of  chloro- 
form to  promote  crystallization.  Note  the  curious  mixtures  of 
solvents  used — ^benzene  and  benzin,  dehydrated  alcohol  and  ben- 
zin. 
However,  the  chief  objection  that  we  have  found  with  the  U.  S.  P. 
assay  method  is  not  the  number  of  manipulations  and  varieties  of 
solvents  involved,  but  that  we  have  been  obtaining  lower  results 
for  both  "combined  and  free"  cantharidin,  by  this  method  than  we 
obtain  for  "free"  cantharidin  alone  by  either  the  Author's  or  the 
original  Baudin  Method;  and  that  the  resulting  crystals  are  not  as 
satisfactory  as  those  obtained  by  the  latter  two  methods.  The 
crystals  obtained  by  both  the  Author's  Method  and  Baudin's  Method 
for  free  cantharidin  are  clean,  white  and  well  formed.  Those  we  have 
obtained  with  the  U.  S.  P.  assay  method  have  been  dark  and  resinous. 
