522  Manganous  Oxides  and  Carbonate.  {Am\J5°rH$.arm" 
MANGANESE  OXIDES  AND  MANGANOUS  CARBONATE.1 
By  A.  Gorgeu, 
When  manganous  hydroxide  is  exposed  to  air  in  presence  of  an 
excess  of  a  manganous  salt,  it  yields  the  manganese  manganite, 
2MnO,Mn02,  with  a  variable  quantity  of  water.  In  presence  of 
oxygen  instead  of  air,  oxidation  is  more  rapid  and  the  proportion  of 
oxygen  in  the  product  is  slightly  higher.  The  product  slowly  absorbs 
oxygen  from  the  air  or  from  oxygen  at  the  ordinary  temperature,  but 
even  after  12  years  the  proportion  of  oxygen  does  not  exceed  that 
required  by  the  formula  Mn02,MnO.  In  presence  of  alkalis  or  alka- 
line earths,  as  is  well  known,  manganous  hydroxide  will  take  up  a 
much  larger  proportion  of  oxygen. 
Solutions  of  manganous  salts  gradually  become  turbid  when  exposed 
to  air,  especially  in  diffused  light,  and  still  more  rapidly  in  bright 
sunlight.  The  change  does  not  take  place  in  an  atmosphere  of  hydrogen. 
With  the  chloride,  sulphate  and  acetate,  the  precipitate  has  the  com- 
position MnO,Mn02,  but  with  the  nitrate,  its  composition  is  2MnO, 
3Mn02.  The  quantity  of  manganese  precipitated  in  this  form  is  only 
a  small  fraction  of  that  present  in  the  liquid.  In  concentrated  solu- 
tions the  amount  precipitated  is  still  less,  and  hence  it  would  seem 
that  precipitation  is  due  to  the  action  of  oxygen  on  a  manganese  salt 
partially  dissociated  by  water. 
Solutions  of  manganous  sulphate,  nitrate,  chloride,  bromide  and 
iodide  may  be  boiled  without  undergoing  any  noteAVorthy  alteration, 
but  the  acetate  yields  more  precipitate  than  at  the  ordinary  tempera- 
ture. The  precipitate  has  the  composition  MnO,Mn02,  the  acetic  acid 
is  continuously  given  off  during  boiling,  hence  it  would  seem  that 
manganous  oxide  is  liberated  in  consequence  of  the  dissociation  of  the 
salt,  and  behaves  like  the  manganous  hydrate  thrown  down  by  alkalis. 
Iodine  dissolved  in  a  solution  of  potassium  iodide  has  little  action 
on  manganous  hydroxide,  scarcely  attacks  manganous  carbonate,  and 
has  no  action  on  the  acetate  and  salts  of  the  strong  acids.  Chlorine 
acts  rapidly  on  the  hydroxides  and  on  all  the  salts.  The  most  con- 
cordant results  were  obtained  with  chlorine-water  and  manganous 
carbonate.  With  the  carbonate  in  excess,  the  product  was  MnO,Mn02, 
but  with  chlorine  in  excess  the  more  highly  oxidized  products, 
MnO,4Mn02  and  MnO,5Mn02,  were  obtained.  Up  to  the  latter  point 
1Compt.  rend.,  cviii,  p.  948  and  1006;  reprinted  from  Jour.  Chem.  Soc,  Sept., 
1889,  p.  829. 
