66  Rapid  Assay  of  Hydrogen  Peroxide.  {Am 
found  inefficient,  was  no  doubt  due  to  the  use  of  a  decomposed 
article.  The  object  of  this  paper  is  to  give  a  method  for  determin- 
ing the  value  of  hydrogen  peroxide,  which  will  enable  the  pharma- 
cist to  make  an  assay  in  the  course  of  a  few  minutes,  the  method  is 
so  expeditious  that,  if  desirable,  the  assay  can  be  made  for  each  pre- 
scription, and  the  result  noted  on  the  prescription  ;  as  a  rule,  how- 
ever, each  bottle  when  opened,  should  be  assayed,  and  if  the 
demand  be  light,  either  for  each  prescription  or  about  once  a  week 
so  as  to  have  a  check  upon  the  rapidity  of  decomposition.  To  the 
question,  "  What  is  the  minimum  value  of  hydrogen  peroxide  suit- 
able for  dispensing  ?"  the  answer  should  come  from  the  practi- 
tioner, but  the  suggestion  is  here  made  that  the  prescription  be  so 
written  as  to  show  the  volume  of  oxygen  which  the  remedy 
should  contain  when  it  is  to  be  used,  thus  enabling  the  pharmacist 
to  give  directions  for  the  dilution  ;  if  this  suggestion  be  enacted 
there  will  result  greater  uniformity  of  strength  than  by  dispensing 
original  packages,  or  by  taking  the  specified  quantity  from  freshly 
opened  bottles,  as  this  is  no  guarantee  that  the  contents  are  of  the 
claimed  strength.  The  method  of  assay  depends  upon  the  follow- 
ing reaction  and  data  :  5  H202  +  K2Mn208  +  3  H2S04  =  5  (02) 
4-  8  H20  -f-  K2  S04  +  2  MnS04 ;  as  one-half  of  the  liberated  oxygen 
comes  from  the  K2M2Os,  one  molecule  of  the  latter  (molecular  weight 
314)  will  liberate  five  atoms  of  oxygen  (weighing  80),  coming  from 
the  H202,  so  that  62*8  grams  K2Mn208  will  liberate  16  grams  oxygen 
which, at  o°  C.  will  occupy  1  ri6  litres  or  at  20°  C.  (an  average  tem- 
perature) almost  12  litres  or  12,000  cubic  centimetres  ;  1  cc.  oxygen  at 
200  C.  therefore  is  liberated  by  the  use  of  0-00525  gm.  K2Mn2Og. 
2-625  gm.  K2Mn208,  dissolved  in  sufficient  distilled  water  to  make  a 
litre  of  solution,  will  liberate,  under  proper  conditions,  500  cc.  oxygen 
from  H202,  so  that  1  cc.  of  this  solution  represents  0-5  cc.  oxygen. 
[Solution  of  permanganate  of  potassium,  containing  3  grams  per 
litre  has  repeatedly  been  shown  to  be  permanent  for  a  long  time 
(Am.  Journ.  Pharm  ,  1892,  565);  so  there  is  no  difficulty  in  keeping 
this  solution  made  up,  provided  it  be  protected  from  dust  and 
light.] 
In  using  this  solution  it  was  soon  found  that  variable  results 
could  be  obtained  if  the  assay  was  made  in  the  presence  of  only  a 
small  quantity  of  water  ;  the  more  rapidly  the  permanganate  was 
added,  the  more  it  would  take;  added  slowly  it  required  less,  the 
