542 
MANUFACTURE  OF  CHLORINE,  ETC. 
it  is  treated  with  carbonate  of  lime,  to  neutralise  any  free  acid  and 
to  decompose  any  sesquichloride  of  iron  or  sesquiehloride  of  alumi- 
nium which  may  be  contained  in  it.  The  neutralised  liquor  is  then 
pumped  up  into  an  elevated  cistern,  in  which  it  is  left  at  rest  for  a 
few  hours,  in  order  that  it  may  deposit  certain  solid  matters  which 
it  now  holds  in  suspension.  The  most  abundant  of  these  is 
usually  sulphate  of  calcium,  due  to  the  somewhat  considerable 
quantity  of  sulphuric  acid  which  is  nearly  always  contained  in  the 
hydrochloric  acid  produced  in  alkali  works  ;  but  there  are  also 
small  quantities  of  sesquioxide  of  iron,  derived  from  the  ses- 
quichloride of  iron  in  the  hydrochloric  acid,  and  sometimes 
partly  from  the  lime  used  in  the  process,  and  larger  or  smaller 
quantities  of  alumina  and  silica,  due  to  the  lime.  These  im- 
purities having  deposited,  the  supernatant  liquor,  which  is  a 
mixed  solution  of  chloride  of  manganese  and  chloride  of  calcium, 
and  is  now  quite  clear,  and  of  a  beautiful  rose-color,  is  run  off 
into  another  vessel,  where  there  is  added  to  it  the  quantity 
of  lime  necessary  to  decompose  the  chloride  of  manganese 
in  it,  and  nearly  an  equivalent  more.  A  blast  of  air  is 
then  injected  into  the  resulting  mixture,  and  what  was  at  first  a 
perfectly  white  mud  (all  the  manganese  in  which  was  in  the  state 
MnO)  soon  becomes  a  very  black  mud,  nearly  all  the  manganese 
in  which  is  in  the  state  of  Mn02.  This  is  then  allowed  to  settle 
for  about  twelve  hours,  at  the  end  of  which  time  it  has  separated 
into  a  denser  black  mud  and  a  supernatant,  clear  solution  of 
chloride  of  calcium.  This  solution  of  chloride  of  calcium  having 
been  drawn  off,  what  remains  is  ready  for  use  in  the  still.  It  is. 
used  as  mud,  without  drying,  being  conveyed  to  the  still  by  pipes, 
and  entering  by  a  hydraulic  lute.  In  the  still  it  meets  with 
hydrochloric  acid,  from  which  it  liberates  chlorine,  at  the  same 
time  re-producing  exactly  such  a  residual  ^solution  as  was  com- 
menced with.  With  this  solution,  the  round  of  operations  is  re- 
commenced, and  so  on,  over  and  over  again,  continually.  The 
samples  I  exhibit  are  portions  of  a  charge  of  manganese 
which,  at  the  works  of  Messrs.  J.  C.  Gamble  and  Sons,  of  St. 
Helen's, — where  this  process  has  been  worked  out,  by  the  liberal 
co-operation  of  Lieut.  Colonel  Gamble,  the  proprietor  of  those 
works,  and  the  invaluable  assistance  of  Mr.  Bramwell,  the  very 
