226 
Hydrogen  Dioxide. 
Am.  Jour.  Pharm. 
May,  1398. 
pose,  to  make  comparisons  of  the  more  prominent  titrimetric  and 
gasometric  methods  under  such  conditions  as  might  be  encountered 
in  practice.  The  experiments  were  confined  to  four  methods,  a  de- 
scription of  which  will  first  be  given. 
Titrimetric  Permanganate  Method. — When  a  solution  of  potas- 
sium permanganate  is  gradually  added,  with  agitation,  to  a  solution 
of  hydrogen  dioxide  containing  sulphuric  acid,  the  permanganate  is 
decolorized  through  the  formation  of  manganous  sulphate,  and  all 
available  oxygen  is  liberated  from  the  hydrogen  dioxide,  together 
with  an  equal  amount  from  the  permanganate.  When  the  last  drop 
of  the  solution  added  leaves  a  permanent  red  color  after  agitation, 
the  reaction  is  ended.  It  proceeds  in  accordance  with  the  following 
equation: 
5H202  +  2KMn04  +  3H2S04  =  502  -f  2MnS04  +  K2S04  +  8H20. 
N 
If  I  c.c.  of  hydrogen  dioxide  solution  is  taken  and  a  - —  solution 
7      &  10 
of  permanganate  used,  the  number  of  cubic  centimeters  required  to 
produce  a  permanent  red  color,  multiplied  by  0-56,  will  indicate  the 
number  of  volumes  of  available  oxygen  yielded  by  one  volume  of 
the  sample. 
Gasometric  Permanganate  Method. — The  reaction  made  use  of  in 
this  method  is  the  same  as  in  the  preceding  one,  the  principal  differ- 
ence being  in  the  direct  measurement  of  the  liberated  oxygen  in- 
stead of  its  calculation  from  the  amount  of  permanganate  consumed. 
The  operation  is  performed  in  a  gasometer,  or  nitrometer,  several 
forms  of  which  have  been  devised.  A  description  of  the  form  best 
suited  to  this  work  and  its  use  will  be  found  in  the  Appendix 
of  the  U.  S.  P.  of  1890,  under  "Gasometric  Estimations,"  and 
in  the  Dispensatories.  The  writer  operated  in  the  following 
manner:  The  measuring  tube,  graduated  to  100  c.c,  is  filled  with 
a  saturated  solution  of  sodium  chloride,  2  c.c.  of  the  sample  are 
accurately  measured  into  the  funnel  tube  and  slowly  let  into  the 
measuring  tube,  care  being  taken  that  no  air  is  admitted.  Ten 
c.c.  of  10  per  cent,  sulphuric  acid  are  then  admitted  in  the  same 
manner,  and  finally  20  c.c.  of  a  2  per  cent,  solution  of  potas- 
sium permanganate.  When  the  reaction  has  nearly  ceased,  the 
tube  is  inverted  a  few  times  to  insure  complete  decomposition  of  the 
hydrogen  dioxide.    This  must  be  repeated  several  times  within  the 
