Am.  Jour.  Pharm.  \ 
January,  1911.  j 
Note  on  Sulphur  Dioxide. 
21 
other  words  the  reaction  between  sulphur  dioxide  and  iodine  might 
be  made,  so  to  speak,  the  connecting  Hnk  whereby  the  typical  repre- 
sentatives of  the  four  different  classes  of  volumetric  solutions, 
namely,  the  permanganate,  iodine,  alkali,  and  silver  solutions,  are 
connected  together  and  their  relative  values  established  and  referred 
back  to  the  silver  solution  which  was  used  in  their  first  standard- 
ization. 
The  standardization  and  checking  of  the  volumetric  solutions  as 
thus  outlined  seems  especially  advantageous  in  the  case  referred 
to  above  (the  volumetric  estimation  of  SOo  and  SO3  when  occur- 
ring together),  for  not  only  would  we  be  able  to  refer  all  the  results 
to  one  standard  instead  of  two  different  standards  (e.g.,  iodine  and 
oxalic  acid),  but  we  could  also  base  the  entire  work  on  a  standard 
which  is  more  readily  kept  unaltered  and  is  more  convenient  than  is 
the  case  with  solid  iodine.  Thus,  for  example,  in  the  estimation  of 
the  SOo  and  SO...  by  the  method  of  Kastle  and  McHargue,  we  might 
base  the  entire  work  on  the  value  of  our  standard  sulphuric  acid 
solution.  By  means  of  the  latter,  the  value  of  the  NaOH  solution 
could  be  readily  ascertained ;  and  by  just  decolorizing  a  definite 
amount  of  the  iodine  solution  with  a  dilute,  freshly  prepared  solution 
of  sulphur  dioxide  (the  strength  of  which  need  not  be  known)  and 
determining  the  total  acidity  by  means  of  the  NaOH  solution,  we 
would  obtain  a  check  on  the  correctness  of  the  assigned  relative 
values  of  the  iodine  and  hydroxide  solutions ;  and  since  the  result- 
ing iodide  could  now  be  determined  by  means  of  the  standard 
silver  solution,  we  would  thus  obtain  a  check  on  the  value  of  the 
iodine  solution  by  direct  reference  to  the  standard  silver  solution. 
In  this  way  we  would  not  only  avoid  the  weighing  and  handling  of 
the  solid  iodine  every  time  we  want  tO'  check  our  solutions,  but 
would  also  base  the  entire  work  on  a  single  standard ;  and  having 
found  that  when  working  with  the  solution  of  pure  sulphur  dioxide 
the  results  obtained  are  in  close  agreement  with  the  theory,  we  could 
feel  more  certain  when  working  in  this  way  than  when  employing 
the  double  standard,  that  the  subsequent  results  with  the  mixture 
of  SO.  and  SO.,,  however  slight  the  variation  may  be  from  the 
results  as  obtained  with  the  pure  SOo,  are  not  due  to  any  error 
in  the  standardization  of  our  solutions,  but  solely  to  the  presence  of 
a  small  amount  of  SO... 
The  following  data  will  illustrate  the  plan  for  standardizing 
all  the  ordinary  volumetric  solutions  by  means  of  pure  mietallic  silver 
