158 
U.  S.  p.  Methcd. 
15  grams. 
150  Mils,  of  a  mixture 
of  2  parts  of  benzene 
and  I  part  purified 
petroleum  benzin. 
2  Mils.  HCl. 
Let  stand  over  night. 
Gradually  warm  to  40° 
C.  and  keep  there  3 
hours,  with  frequent 
shaking.  Cool  and 
decant  off  100  Mils. 
Bvaporate  to  about  5 
Mils. 
Add  5  Mils.  CHCI3  and 
let  evaporate  in  warm 
place. 
Add  10  Mils,  of  a  mix- 
ture of  equal  parts  of 
dehydrated  alcohol 
and  purified  petro- 
leum benzin  satur- 
ated with  pure  can- 
tharidin,  let  stand  15 
minutes.  Decant 
liquid  through  a  pel- 
let of  purified  cotton 
and  reject  filtrate. 
Wash  crystals  with  suc- 
cessive portions  of 
saturated  cantharidin 
solution,  prepared  as 
directed  above,  until 
free  of  coloring 
matter,  and  pour 
through  the  same 
pellet  of  cotton. 
Wash  cotton  with  small 
amount  hot  CHCI3 
and  add  washings  to 
tarred  beaker. 
JBvaporate  solvent. 
Dry  V2  hour  at  60°  C. 
Weigh. 
Resulting  weight  equals 
cantharidin  in  10 
grams  of  cantharidin. 
This  should  give  both 
free  and  combined  can- 
tharidin. 
Cantharides  Assay. 
Methods  Used. 
Author's  Method. 
10  grams. 
30  Mils.  CHCI3. 
Let  stand  over  night. 
Shake    during  several 
hours. 
Filter  and  wash  with 
70  Mils.  CHCI3. 
Evaporate  on  water 
bath. 
Treat   residue   with  5 
Mils.  CS2. 
Am.  Jour.  Pharm. 
March,  1920. 
Bandin's  Method. 
25  grams. 
100  Mils.  CHCl,. 
Let  stand  over  night. 
Shake  2  to  3  hours. 
Filter  on  covered  filter. 
Collect  60  Mils,  of  the 
filtrate  representing 
15  grams. 
Evaporate  on  water 
bath,  and  proceed  just 
the  same  as  the  Au- 
thor's Method. 
Transfer  to  small  tarred 
filter  paper,  4  cm. 
diameter. 
Wash  with  10  Mils.  CS2 
in  small  portions. 
Dry  filter  at  60°  C. 
Weigh. 
Add  0.010  grams  for  sol- 
vent action  of  CS2. 
This  should  give  free 
cantharidin. 
To  obtain  combined  as 
well,  add  2  Mils.  HCl 
to  the  original  chloro- 
form. 
This  should  give  free 
cantharidin.  To  ob- 
tain combined  as  well, 
add  2  Mils.  HCl  to  the 
original  chloroform. 
