NEW  PROCESS  FOE  REGENERATING  OXIDE  OP  MANGANESE.  255 
of  loss,  a  charge  of  manganese,  once  put  into  a  still,  when 
treated  by  this  process,  not  only  never  needs  to  be  replaced,  but 
never  needs  even  to  be  added  to,  while  it  will  liberate  an  equiv- 
alent of  chlorine  every  few  hours  for  literally  any  length  of  time. 
The  starting-point  of  any  process  for  the  regeneration  of  the  oxide 
of  manganese  employed  in  the  manufacture  of  chlorine,  must, 
of  course,  be  that  residue  which  is  known  as  "  still-liquor," 
being  that  which  remains  in  the  stills  when  oxide  of  manganese 
and  hydrochloric  acid  have  been  digested  together  until  all  the 
chlorine  which  the  oxide  is  capable  of  liberating  from  the  acid 
has  been  liberated  and  given  off.  When  working  with  a  native 
oxide  of  manganese,  the  still  liquor  contains,  in  addition  to  a  quan- 
tity of  protochloride  of  manganese,  equivalent  to  the  quantity  of 
oxide  of  manganese  which  has  been  dissolved,  a  considerable  quan- 
tity of  free  acid,  and  more  or  less  chlorides  of  iron  and  other  bases 
due  to  the  native  oxide  of  manganese  being  always  more  or  less  as- 
sociated with  other  oxides.  When  working,  however,  with  the  arti- 
ficial oxide  of  manganese  produced  as  is  about  to  be  described,  the 
still-liquor  contains  scarcely  anything  whatever  but  protochloride 
of  manganese  ;  and  the  new  process  consists  simply  in  first 
adding  an  equivalent  of  lime  to  this  liquor,  without  removing 
the  liquor  from  the  still,  and  then  blowing  atmospheric  air 
through  the  resulting  mixture  of  protoxide  of  manganese  and 
solution  of  chloride  of  calcium.  The  white  protoxide  is  thereby 
rapidly  converted  into  a  very  dark-colored  higher  oxide,  and 
when  this  product  has  been  allowed  to  subside  from  the  solution 
of  chloride  of  calcium  in  which  it  was  formed,  and  the  greater 
part  of  that  solution  has  then  been  drawn  off  from  it,  it  is  ready 
to  be  treated  with  hydrochloric  acid,  from  which  it  then  liberates 
chlorine,  with  reproduction  of  exactly  as  much  protochloride 
of  manganese  as  was  commenced  with.  From  this  point  the 
very  simple  series  of  operations  described  is  repeated  just  as 
before,  and  so  on,  over  and  over  again,  for  any  required  number 
of  times.  The  manganese  is  thus  constantly  undergoing, 
always  in  one  and  the  same  vessel,  around  of  regularly  recurring 
changes  of  state  of  combination,  by  which  it  passes,  first  from 
the  state  of  protochloride  to  that  of  protoxide,  next  from  the 
state  of  protoxide  to  that  of  a  higher  oxide,  capable  of  libera- 
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