544  Preservation  of  Hydrogen  Peroxide.   { A^ember  ^i?1' 
Discussion  of  Results. 
From  the  results  of  series  I,  it  is  evident  that,  contrary  to  the 
general  assumption,  pure  hydrogen  peroxide  is  a  very  unstable  sub- 
stance and  that  its  stability  is  greatly  increased  by  the  addition  of 
small  amounts  of  acid.  The  addition  of  salts  of  the  alkali  and  alka- 
line-earth metals  does  not  appear  to  have  any  marked  effect.  In  two 
or  three  cases  the  resulting  solutions  are  more  stable  and  in  the  other 
cases  they  are  less  stable.  By  the  addition  of  acetanilide  alone  to  the 
solution  its  stability  was  greatly  increased,  the  decomposition  being 
about  2.7  per  cent,  in  5  months. 
From  series  II  the  same  conclusion  may  be  reached  in  regard  to 
the  stability  of  pure  hydrogen  peroxide,  and  the  effect  of  acids 
and  of  acetanilide  upon  the  solution.  The  combined  effect  of  acid 
and  its  salt  and  of  free  silica  is  here  brought  out  and  it  is  evident  that 
in  acidified  solutions  the  salts,  at  the  strength  in  which  they  were 
used,  have  no  influence  upon  the  stability  of  the  solutions,  while  free 
silica  renders  them  less  stable. 
In  series  III  a  study  was  made  of  the  effects,  in  varying  strengths, 
of  the  different  acids  sometimes  used  in  acidifying  the  commercial 
solution  of  hydrogen  peroxide.  Phosphoric  acid  gave  the  best 
results  at  all  the  concentrations  used.  It  will  be  noted,  however,  that 
the  best  preserved  solution  had  lost  in  strength  nearly  30  per  cent, 
in  7  months  and  that  such  a  solution,  although  more  stable  than  the 
chemically  pure  peroxide,  would  not  answer  at  all  for  commercial 
purposes. 
In  series  IV,  V,  and  VI  there  were  introduced  into  the  solutions 
of  pure  peroxide  all  of  the  mineral  impurities  likely  to  occur  in 
a  commercial  preparation,  and  in  the  maximum  concentrations  in 
which  they  might  be  found.  In  order  to  cover  the  ground  completely 
and  so  that  the  different  series  might  serve  as  a  check  upon  each 
other,  three  different  acids  were  used  with  their  corresponding 
salts.  Each  impurity  was  used  with  and  without  acetanilide  so  that 
the  effect  of  this  preservative  might  be  seen  in  all  possible  cases. 
Several  different  brands  of  commercial  peroxide  were  examined 
and  the  total  mineral  residue  was  always  found  to  be  less  than 
.05  per  cent.  This  residue  was  found  to  consist  in  all  cases,  of  over 
50  per  cent,  silica,  so  that  the  total  mineral  matter  other  than  silica 
was  less  than  1  part  in  4000. 
The  results  obtained  in  the  last  3  series  of  experiments  are 
