536 
IODINE  FROM  THE  ASHES  OF  SEA-WEEDS. 
of  evaporating  a  large  quantity  of  useless  water,  and  consequently 
save  expense. 
In  regard  to  the  separation  of  the  mixed  salts.  They  are 
taken  out  in  the  order  of  their  insolubility,  sulphate  of  potash 
being  the  first  parted  with  by  the  ley,  as  it  contracts  in  the 
evaporation.  There  are  two  methods  of  obtaining  this  salt ; 
that  which  is  adopted  depending  upon  whether  the  operator  wishes 
to  crystallize  out  the  salt,  or  merely  to  deposit  it  during  the  boil- 
ing ;  if  the  crystals  are  wanted,  the  ley  from  the  steeps  should  not 
exceed  30°  on  the  hydrometer,  and  should  be  boiled  until  it 
shows  a  pellicle  on  the  surface,  when  a  little  should  be  taken  out 
and  blown  upon  by  breath  ;  this  will  occur  when  it  marks  on  the 
hydrometer  42°  to  44°.  The  fire  should  now  be  drawn  out, 
and  the  hot  ley  ladled  into  the  crystallizing  pans,  which  are  best 
made  of  cast  iron ;  when  cold,  a  layer  of  the  salt  will  be  found 
adhering  to  the  sides  of  the  vessel;  this  should  be  allowed  to 
remain  after  the  liquor  is  removed,  and  five  or  six  different  panfuls 
allowed  to  crystallize,  one  after  the  other,  when  the  salt  mey  be 
removed  to  make  room  for  another  quantity.  This  plan  is, 
however,  now  seldom  adopted,  as  it  entails  a  loss  of  time  in  the 
cooling,  and  takes  up  too  many  vessels. 
The  other  plan  is  this  :  the  ley  at  S69  or  40°  is  evaporated 
up  to  62°  or  64°  at  one  boiling.  When  it  reaches  44°  it  then 
begins  to  part  with  the  sulphate  of  potash,  which  falls  down  to 
the  bottom  of  the  pan,  in  small  scaly  crystals,  of  a  grey  color  ;  as 
these  are  apt  to  adhere  to  the  sides  of  the  pan,  a  scraper  of  iron, 
tipped  with  steel,  is  used  to  keep  the  sides  free,  and  prevent 
caking,  as  this  would  endanger  the  safety  of  the  vessel.  The 
scraper  is  an  iron  rod  about  6  feet  in  length,  with  the  lower  end 
broadened  out  to  about  3  inches  in  width,  and  kept  sharp.  The 
salt,  as  it  is  scraped  down  and  deposited,  is  scooped  out  with  a 
long  wooden-handled  iron  shovel,  perforated  with  small  holes  to 
allow  the  water  to  drain  off;  a  half  cask  with  a  few  holes  for 
drainage  is  placed  with  its  edge  over  the  side  of  the  pan  to  receive 
the  wet  salt ;  this  allows  the  liquor  to  drain  back  into  the  boiler. 
After  the  boiling  has  continued  until  a  strong  pellicle  is  formed 
on  the  ley,  which  will  occur  at  62°  or  64°,  the  fire  should  be 
withdrawn,  and  after  standing  20  minutes  or  so,  the  contents 
ladled  into  the  coolers.    A  further  deposit  of  sulphate  will  be 
