if  neutral,  a  small  quantity  of  such  substances  as  acetanilid  or  boric  acid
are  added.  The  presence  of  ferric  oxide,  alumina,  silica,  etc.,  causes  rapid
decomposition  of  these  solutions.  Hydrogen  dioxide  is  a  powerful
oxidizing  (also  reducing)  agent,  through  its  decomposition  into  nascent
oxygen.    It  bleaches  organic  pigments,  hair,  feathers,  bone,  etc.    -

Oxidizing  Reactions. — Hydrogen  dioxide  oxidizes  :

(i)   Sulphides  to  sulphates,

PbS       1       4HaOa     -        PbS04     4      4HaO.
H2S  4HaOa  HaS04      -     4HaO.
(2)  "cms"  iicids  and  salts  to  "ic"  state,

^^  HaSOa  HaOa  HaSO^      :       HaO.
H3PO3       :       HaC^a       ^     H3PO4      '       HaO.
2FeS04      ;       HaOa     -\-     HaS04     -=     Fea(S04)8     -f     aHaO.
(3)  Arsenic,    arsenous   oxide,  aluminum,    iron,  magnesium,  lead,  etc.,  to  their
highest  oxides,

Mg     r       2HaOa       -     MgO(OH)a     -V     HaO  (MgOa  -h  aHaO).
(4)  The  hydroxides  of  barium,  calcium,  and  strontium  are  converted  into  their
•  peroxides.
Ba(OH)a     -f     HaOa      -     BaOa     -      aHaO.
(5)  Hypochlorous  and  hypobromous  acids  and  their  salts  yield  their  respective
halogen  acids  or  salts,

HCIO  HaOa       -     HCl      •       HaO     -f     Oa.
CaOCla     :       HaOa  CaCla    :       HaO      ^      Oa.
(6)  The  halogens  are  converted  into  their  binary  acids,  ^

Cla      r     HaOa     =     2  HCl     +     Oa.
OXYGEN  AND  HYDROGEN.  199

Redocini^  Reactions. —

II

(7)  Potassium  ferro-cyanide  [K4Fe(CN)e],  in  acid  solution,  is  oxidized  to  the

fem-cyanide     [KsFe(CN)6].      2K4Fe(CN)6     ,     2HCI  -r    HaOa    -^    2K8Fe(CN)6
--   2KCI   T-  2H2O.     In  a^aZf'n^  solution,  reduction  takes  place.
2KsFe(CN)6    -}-     2KOH     4      HaOa      -     2K4Fe(CN)6     -f-     aHaO     +     0%.
(8)  Silver  oxide  is  reduced  to  metallic  silver,

AgaO     -r       HaOa  HaO     -f     Ag2      +         0«.
(9)  Brown  lead  peroxide  is  reduced  to  yellow-oxide,

Pb02     4      HaOa     -  =     PbO     -f-     HjO     -f     O2.
