PROTOXIDES  OF  IRON,  MANGANESE,  AND  TIN.  527 
SIMPLE  METHOD  OF  PREPARING  THE  PROTOXIDES  OF  IRON, 
MANGANESE  AND  TIN. 
By  Prof.  Liebig. 
Prof.  A.  Vogel's  description  of  the  preparation  of  his  excellent 
polishing  powder  from  protoxalate  of  iron  has  been  an  induce- 
ment to  the  investigation  of  some  other  oxalates,  especially  the 
protoxalates  of  manganese  and  tin,  which,  as  I  have  found,  may 
be  obtained  perfectly  anhydrous. 
Protoxalate  of  manganese  is  obtained,  like  the  iron  salt,  by 
precipitating  a  protosalt  of  manganese  with  free  oxalic  acid ;  it 
is  a  white  pulverulent  precipitate,  with  a  tinge  of  red.  When 
heated  to  212°— 248°  F.,  it  loses  all  its  water ;  and  when  heated 
in  this  state  in  a  common  combustion-tube,  it  furnishes  carbonic 
acid  and  carbonic  oxide  gases  in  exactly  equal  volumes,  and 
leaves  a  pure  protoxide  of  manganese  of  a  pale  green  color,  which, 
when  touched  with  a  red-hot  body,  ignites  and  smoulders  into 
protoperoxide  of  manganese. 
Protoxalate  of  tin  behaves  in  exactly  the  same  manner,  and 
these  two  preparations  may  be  employed  in  the  formation  of  pure 
protoxide  of  manganese  or  tin  as  a  class  experiment.  The  de- 
composition of  protoxalate  of  iron  described  by  Vogel,  furnishes 
a  protoxide  of  iron,  which  is  not  quite  free  from  metallic  iron, 
but  which  is  at  any  rate  the  purest  that  can  be  prepared  in  an 
anhydrous  state  ;  it  ignites  spontaneously  in  the  air,  and  burns 
like  a  pyrophorus  to  oxide  of  iron.  Protoxalate  of  iron  contains 
in  1  atom  (C4  Ofi,  2  FeO)  exactly  4  equivs.  of  water,  as  found  by 
Vogel ;  when  heated  nearly  to  its  point  of  decomposition,  it 
loses  another  atom  of  water  ;  and  the  great  hardness  of  the  oxide 
of  iron  obtained  from  it  by  slow  combustion  in  the  air  depends 
evidently  upon  the  dry  combustion  of  the  protoxide  of  iron. 
I.  3-067  grms.  of  protoxalate  of  manganese,  rlried  at  212°  F., 
gave  1-642  grm.  of  protoperoxide=:  50-02  per  cent,  of  protoxide 
^(C203,  MnO). 
II.  3-941  grms-  of  protoxalate  of  iron,  dried  at  302o-320°F., 
left  after  calcination  1-857  grm.  oxide  of  iron  =42-4  per  cent, 
of  protoxide  of  iron  ;  the  formula  C4  06,  FeO  +  3Aq  requires 
42-11  per  cent. 
