MANUFACTURE  OF  CHLORINE,  ETC. 
539 
cost  of  the  manufacture  of  chlorine,  greatly  increases  the 
quantity  of  chlorine  which  can  be  practically  obtained  from  a 
given  quantity  of  hydrochloric  acid,  and,  moreover,  enables  the 
manufacture  of  chlorine  to  be  carried  on  without  the  production 
of  any  offensive  residue,  I  have  ventured  to  think  that  a  very 
brief  account  of  it  might  not  be  without  interest  to  this  Section. 
What  has  hitherto  been  the  ordinary  process  of  manufacturing 
chlorine  consists  simply  in  digesting  with  hydrochloric  acid  ores 
containing  peroxide  of  manganese.  The  reaction  which  takes 
place,  besides  liberating  chlorine,  produces  chloride  of  manganese, 
which  remains  behind  a  solution  after  the  chlorine  has  gone  off, 
and  has  hitherto  been  usually  thrown  away.  There  have  been 
proposed  and  tried  a  great  number  of  processes  for  transforming 
this  chloride  into  peroxide  for  use  over  again  ;  but  the  only  one 
of-  them  which  has  met  with  the  slightest  measure  of  practical 
success,  prior  to  that  which  is  the  subject  of  this  paper,  is  the 
one  which  is  known,  from  the  name  of  its  inventor,  as  Dunlop's 
process.  Dunlop's  process  decomposes  the  chloride  of  man- 
ganese by  heating  its  solution,  under  a  pressure  of  from  two  to 
four  atmospheres,  with  milk  of  carbonate  of  lime,  and  then,  in 
the  dry  way,  transforms  the  resulting  carbonate  of  manganese 
into  a  mixture  or  compound  of  two  equivalents  of  peroxide  with 
one  equivalent  of  protoxide,  by  subjecting  it  for  forty-eight 
hours  to  the  action  of  air  at  a  temperature  of  about  600°  Fahr. 
The  product  of  Dunlops's  process  is  a  suflficiently  satisfactory 
one,  containing  about  72  per  cent,  of  Mn02;  but  the  process  re- 
quires a  very  formidable  amount  of  apparatus,  and,  in  this  and 
other  ways,  is  so  costly  that  its  use  has  never  been  extended 
beyond  a  single  firm  of  manufacturers. 
Three  years  ago  I  began  to  endeavor  to  work  out  the  idea  of 
decomposing,  by  either  lime  or  magnesia,  the  chloride  of  man- 
ganese in  the  residual  liquors  of  the  chlorine  manufacture,  and 
then  blowing  air  through  the  resulting  mixture  of  hydrated  pro- 
toxide of  manganese  with  solution  of  chloride  of  calcium,  or  of 
chloride  of  magnesium,  as  the  case  might  be.  I  took  for  granted 
that  one-half  of  the  protoxide  of  manganese  so  treated  was  the 
largest  proportion  of  it  that  could  thereby  be  converted  into 
MnOa — in  other  words,  that  one  could  obtain  only  sesquioxide 
