IODINE  FROM  THE  ASHES  OF  SEA-WEEDS.  587 
found  in  the  boilers  ;  this  is,  of  course,  added  to  the  rest  in  the 
cask  and  allowed  to  drain. 
The  liquor  being  now  deprived  of  its  sulphate  of  potash,  will, 
upon  cooling,  deposit  a  plentiful  crop  of  white  crystals  of  chlo- 
ride of  potassium  all  round  the  sides  and  bottom.  This  liquor, 
when  cold?  must  now  be  ladled  into  the  boilers  again  for  further 
evaporation ;  the  bottom  of  the  cooler,  from  which  it  has  been 
taken,  cleaned  out  and  put  into  tubs  with  small  holes  in  the 
bottom  to  drain  the  salt,  the  liquor  being  preserved  and  added 
to  that  in  the  boiler ;  the  crystals  on  the  sides  will  drain  down 
to  the  bottom  in  a  few  hours,  and  then  may  be  removed,  mixed 
with  the  dried  bottoms  and  sent  to  market. 
The  liquor  from  which  these  crystals  were  obtained,  and  which 
was  returned  again  to  the  boilers,  is  now  to  be  evaporated  as 
before  ;  this  time  the  boiling  is  to  continue  until  the  hydrometer 
marks  66°  or  68°  ;  and  during  this  boiling  the  soda  salts  begin 
to  be  deposited  in  the  same  manner  as  the  sulphate  was  in  the 
first.  The  pan  must  be  diligently  scraped  and  the  salt  put  into  a 
tub,  and  set  to  drain  over  the  edge  of  the  pan  as  before,  keeping 
this  deposit  and  the  sulphate  separate.  When  a  pellicle  is 
formed  as  before,  which  will  be  at  66°  or  68°,  the  same  mode  of 
procedure  is  to  be  adopted  as  in  the  first  case,  and  a  further 
deposit  of  crystals  obtained.  When  the  liquor  is  cold,  it  is 
again  to  be  boiled,  and  the  same  process  followed  exactly  as  in 
the  former  cases.  The  deposit  at  this  third  boil  being  still  soda 
salts,  may  be  mixed  with  the  salt  from  the  second  boil;  the 
liquor  should  be  brought  to  mark  72°,  and  again  set  aside  to  cool. 
Some  manufacturers  now  stop  the  further  concentration,  but  the 
majority  prefer  boiling  a  fourth  time,  proceeding  exactly  as 
directed  for  the  three  previous  boils  ;  all  the  deposited  salt  which 
falls  during  the  last  three  boils,  being  soda  salts,  are  stirred  to- 
gether. The  first,  or  sulphate  of  potash,  stored  by  itself,  and 
the  contents  of  the  crystallizing  vessels,  or  chloride  of  potassium, 
also  kept  separate.    The  liquor  at  the  last  boil  should  mark  74°, 
The  pans  in  which  the  evaporation  is  conducted  are  generally 
made  about  7  J  feet  across  the  mouth,  with  a  depth  of  3 h  feet. 
They  should  be  set  so  that  the  flame  may  not  strike  the  bottom 
of  the  pan,  but  play  round  the  sides  ;  this  is  done  by  setting  the 
bottom  solid  on  clay,  and  building  a  small  arch  in  front,  so  the 
