420 
Peroxide  of  Hydrogen. 
f  Am.  Jour.  Pharna. 
t      Aug.,  1879. 
oxygen  was  so  violent  as  to  amount  almost  to  explosion.  When  kept 
in  solution  in  the  laboratory  a  10-volume  solution  of  peroxide  is  mod- 
erately stable.  During  1878  tests  were  made  of  a  sample  by  the 
bichromate  method  over  mercury ;  the  strength  gradually  decreased 
from  9*o,  on  August  2,  to  7-2,  on  October  24.  A  few  drops  of  ether 
were  now  added  to  250  cc.  of  that  sample  of  October  24,  and  the 
tests  continued  until  December  24,  when  it  still  was  7*2. 
Ether  seems  to  preserve  it,  a  fact  which  has  been  known  for  some 
time.  This  was  also  mentioned  to  me  by  Dr.  Messel,  of  Silvertown,, 
in  August,  1878,  a  method  I  have  used  ever  since.  It  is  stated  in  all 
our  text-books  that  peroxide  of  hydrogen  is  neutral  to  test-papers. 
Now,  all  commercial  peroxide  is  faintly  acid  with  the  excess  of  hydro- 
fluoric or  hydrofluosilicic  which  is  added  and  which  should  be  estimated 
in  each  sample  before  using  it. 
I  have  used  peroxide  of  hydrogen  since  1873,  and  latterly  in  com- 
paratively large  quantities,  and  I  have  made  it  a  rule  to  examine  each 
purchase  as  follows  :  100  cc.  of  the  peroxide  was  evaporated  to  dry- 
ness with  10  cc.  N  soda,  ignited,  and  taken  up  again  with  water.  N 
acid  was  then  added  to  neutrality,  chromate  of  potash,  and  finally 
N 
titrated  with  —  nitrate  of  silver.    The  results  of  many  experiments 
10 
upon  this  one  sample  showed  that  100  cc.  of  peroxide  neutralized  0*2 
N 
cc.  of  N  soda  and  consumed  3  4  cc.  of  —  nitrate  of  silver.    On  the 
10 
evaporation  to  dryness  of  the  peroxide  by  itself  a  very  pungent  acid  is 
liberated,  and  which  can  be  easily  told  is  not  hydrochloric.  In  order 
to  show  the  moderate  stability  of  peroxide  of  hydrogen,  I  have  lately 
had  a  sample  sent  me  of  commercial  peroxide  which  was  at  least  fifteen 
months  old.  When  treated  with  bichromate  over  mercury  it  gave  7 
volumes  of  oxygen,  and  I  know  that  no  special  care,  or  indeed  care  of 
any  kind,  was  bestowed  upon  the  sample. 
Having,  then,  a  ready  method  of  testing  its  contained  amount  of 
active  material,  it  remains  only  for  me  to  show  that  peroxide  of  hydro- 
gen is  an  exceedingly  useful  oxidizing  agent,  for  it  oxidizes  by  reason 
of  its  loosely  combined  oxygen,  and  when  an  excess  is  added  to  any 
substance  or  to  any  solution,  that  excess  is  readily  eliminated,  leaving, 
only  as  a  residue  that  most  neutral  substance,  water. 
There  are  many  substances  often  seen  in  the  laboratories  of  alkali. 
