Am*May!'i886arm*}  Pharmaceutical  Notes  from  Purdue  University.  227 
Volumetric  Estimation. — After  making  the  tests  noted  above, 
an  effort  was  made  to  find  a  ready  method  of  titrating  sulphuric  in 
presence  of  sulphurous  acid.  A  sample  of  sulphurous  acid  free  from 
sulphuric  was  titrated  both  with  caustic  soda  and  with  iodine  ;  but 
the  former  resuH  was  too  high.  This  discrepancy  was  probably  due 
to  dissolved  carbonic  acid,  which  could  not  be  expelled  by  heat  with- 
out loss  of  sulphurous  acid  also.  It  then  remaiued  either  to  oxidize 
the  sulphurous  acid  first  with  decinormal  solution  of  iodine  in  pres- 
ence of  starch  and  titrate  with  decinormal  soda  (deducting  for  both 
sulphuric  and  hydriodic  acids  formed)  to  determine  the  sulphuric 
acid,  or  to  expel  the  sulphurous  with  any  carbonic  acid  by  heat  before 
adding  the  alkali.  In  the  first  case,  the  two  acids  were  determined 
in  one  portion,  the  iodide  of  starch  being  nearly  decolorized  with 
heat  before  adding  the  soda  ;  by  the  latter  method  separate  portions 
were  required,  and  at  a  temperature  of  70°  C.  several  hours  were  re- 
quired to  expel  all  the  sulphurous  acid. 
To  test  these  methods,  solutions  of  sulphuric  and  sulphurous  acids 
were  titrated  separately,  and  measured  quantities  were  then  mixed  to 
be  titrated  together. 
25  c.c.  H2S04  required  25*6  c.c.  decinormal  HNaO,  either  in  pres- 
ence or  absence  of  iodide  of  starch;  hence,  this  volume  contained 
0-125  gm.  H2S04. 
25  c.c.  S02  required  8*4  c.c.  decinormal  solution  of  iodine;  hence, 
this  volume  contained  0*027  gm.  S02. 
Measured  quantities  were  then  mixed  and  both  constituents  deter- 
mined in  the  same  portion  as  follows  : — 
h2so4.  so2. 
Taken.  Found.  Taken.  Found. 
No.  1                              -125  -125  027  '027 
No.  2                              -250  -254  -027  '027 
No.  3                              -125  "129  -054  -054 
Mixtures  were  also  prepared,  and  the  H2S04  determined  after  ex- 
pulsion of  S02  by  heat,  as  follows  : — 
H2S04.  S02. 
Taken.          Found.  Taken.  Found. 
No.  4                              -125            125  -027  '027 
No.  5                              "250            -250  '027  '027 
These  results  are  considered  satisfactory ;  but  after  developing 
