Utilization  of  Recovered  Salt. — The  salt  as  removed  from  the
filter  is  of  varying  degrees  of  purity  according  to  the  thoroughness  of
the  purification  of  the  waste  lye,  whether  hydrochloric  or  sulphuric
acid  has  been  used  as  the  neutralizing  agent,  whether  a  portion  of
the  crude  sulphate  has  been  separated  by  fractional  crystallization,
previously  described,  and  according  to  the  thoroughness  of  the
washing  process.  The  impurities  may  be  divided  into  two  classes,
viz.,  organic  and  inorganic.  The  former  comprise  fatty,  resinous
and  albuminous  matter  imperfectly  removed  from  the  waste  lye  and
crude  glycerin  remaining  after  the  washing  process  in  the  filter.
The  latter  may  compromise  sodium  hydrate  and  carbonate,  incom-
pletely neutralized  in  the  preliminary  purification  of  the  waste  lye
and  adhering  in  solution  to  the  salt  and  sodium  sulphate  resulting  from
the  use  of  sulphuric  acid  in  neutralization,  and  oxide  of  iron  from
the  interior  of  the  evaporator,  or  iron  salts  not  completely  removed
in  the  purification  of  the  waste  lye.  In  addition  there  is  more  or
less  water.  The  salt  may  be  used  directly  in  the  kettle  without
further  treatment.  When  dark  it  is  not  without  discoloring  effect
upon  the  soap  which,  while  not  affecting  rosined  soap  to  an  appreciable
degree  prevents  its  use  for  graining  white  soap.  It  may  be  purified,
when  desirable  and  practicable  to  use  it  in  saturated  solution,  by
dissolving  it  in  water;  treating  it  with  sufficient  diluted  sulphuric
acid  to  aid  removal  of  the  organic  matter  by  filtration,  and  treating
the  filtrate  thus  purified  with  soda-ash  to  precipitate  the  iron  salts,
whereupon  it  is  again  filtered  and  is  ready  to  be  used.
