Am.  Jour.  Pharm. 
May,  1898. 
Hydrogen  Dioxide. 
231 
No  barium  salts  or  fluorides  were  detected  by  the  U.S. P.  tests. 
N 
The  limit  of  acid  (0-5  c.c.  of  _  soda  for  50  c.c.)  was  exceeded  in 
three  samples.  The  limit  of  residue  (0  25  grammes  for  50  c.c) 
was  exceeded  in  one.  Nos.  I,  II,  and  III  are  aqueous  solutions, 
stated  to  contain  respectively  10,  15,  and  30  volumes  of  available 
oxygen,  while  No.  IV  is  an  ethereal  solution  claimed  to  contain  25 
per  cent,  of  hydrogen  dioxide.  These  claims  as  to  strength  are  rea- 
sonably well  supported  by  the  results  obtained.  It  will  be  seen  that 
with  some  samples  the  results  by  the  different  methods  vary  more 
than  with  others,  the  differences  being  greatest  in  the  case  of  Sam- 
ple IV.  Subsequent  experiments  showed  the  discrepancies  in  this 
case  to  be  at  least  partially  due  to  the  presence  of  ether,  and  the 
fourth  method  to  be  the  most  trustworthy  for  the  assay  of  ethereal 
solutions.  The  first,  third,  and  fourth  methods  are  fairly  well  in 
accord  with  each  other,  but  the  second  frequently  gave  figures  dif- 
fering not  only  from  those  obtained  by  other  methods,  but  also  dif- 
fering widely  among  themselves  in  duplicate  estimations.  This 
method,  because  of  its  seeming  unreliability,  was  left  out  of  consid- 
eration in  later  experiments. 
Estimation  in  Presence  of  Preservative  Agents  In  the  experi- 
ments to  be  described,  Sample  II  was  used,  as  it  proved  to  be  the 
purest  of  the  aqueous  solutions  at  the  writer's  disposal.  The  mix- 
tures were  prepared  by  diluting  13-35  cc-  °f  this  solution,  contain- 
ing 15-45  volumes  of  available  oxygen,  to  100  c.c.  with  distilled 
water,  after  adding  a  definite  quantity  of  the  substance  whose  influ- 
ence on  the  methods  was  to  be  determined.  Five  c.c.  of  the  dilu- 
tion represent  1  c.c.  of  a  solution  of  two-thirds  the  above  strength, 
or  10  3  volumes.  It  was  thought  best  to  base  the  calculations  on 
this  latter  standard  of  strength,  as  being  the  more  customary  one. 
The  percentages  given  in  the  table  below,  of  preservative  substances 
added,  were  also  based  on  this  standard.  In  some  cases  these  were 
added  in  the  quantity  that  would  be  required  to  make  a  saturated 
solution  in  the  amount  of  10  volume  solution  present;  in  other  cases 
much  larger  quantities  were  taken.  The  results  are  given  in 
volumes  of  available  oxygen. 
