ECKKi.l  SALT    INDUSTRY    IN    UTAH    AND    CALIFORNIA.  491 
from  the  tracks  of  the  Saltair  Railway.  The  salt  first  passes  through 
a  Hersey  rotary  drier.  This  consists  of  two  concentric  cylinders 
clamped  together  and  rotating  on  bearings  which  support  the  outer 
cylinder.  The  inner  cylinder,  or  steam  drum,  is  about  3  feet  in  diam- 
eter, and  is  fed  with  steam  from  the  boiler.  The  outer  cylinder  is 
6  feet  in  diameter  and  45  feet  long.  Angle  irons  are  fixed  at  intervals 
around  its  inner  circumference.  The  drier  is  set  at  a  slight  inclina- 
tion, say  about  one-half  inch  to  the  foot.  The  salt  is  fed  into  the 
space  between  the  two  cylinders  at  the  upper  end  of  the  drier,  and  as 
the  drier  revolves  the  salt  travels  slowly  toward  its  lower  end,  where 
it  is  discharged  into  a  conveyer.  This  carries  it  to  the  second  floor  of 
the  mill,  from  which  it  falls  through  a  chute  to  the  first  set  of  a  series 
of  six  rolls.  After  passing  through  the  first  set  of  rolls  the  crushed 
material  is  again  elevated  to  the  second  floor  and  sent  over  a  shaking 
sieve,  which  acts  as  a  separator,  allowing  the  fine  stuff  to  go  to  the 
bagging  room,  while  the  coarser  material  is  again  dropped  through  a 
chute  to  the  second  pair  of  rolls,  which  are  set  closer  than  the  first 
set  and  therefore  give  a  finer  product.  This  is  again  sieved,  sepa- 
rated, and  crushed  in  still  finer  rolls,  the  process  continuing  until  the 
material  has  passed  through  six  sets  of  rolls  of  increasing  closeness, 
passing  over  sieves  after  each  crushing.  The  sieves  are  of  40  mesh 
at  their  upper  end  and  30  mesh  at  the  lower  end,  and  feed  into  differ- 
ent bins.  Fans  are  placed  over  the  top  of  each  sieve  and  also  in  the 
rolls  and  driers.  These  fans  take  off  the  very  lightest  and  finest 
material,  and  their  product  is  conveyed  into  a  room  where  it  is 
pressed  for  cattle  feed.  As  the  magnesium  and  sodium  sulphates  are 
considerably  lighter  than  the  sodium  chloride,  the  use  of  these  fans 
takes  out  much  of  the  sulphates  and  purifies  the  salt  very  appreciably, 
as  shown  by  the  analyses  below.  This  fine  material,  relativel}7  high 
in  sulphates,  is  mixed  with  0.5  to  2  per  cent  of  powdered  sulphur, 
dampened  slightty,  and  pressed  into  boxes  or  blocks.  These  are 
loaded  on  little  trucks  and  run  into  a  drying  tunnel,  where  they  are 
baked  by  direct  heat. 
That  such  a  device  would  effectively  accomplish  the  separation  of 
the  sulphates  from  the  salt  might  perhaps  be  doubted,  but  the  efficiency 
of  the  fans  is  abundantly  demonstrated  by  comparison  of  analyses  of 
crude  and  of  refined  salt.  A  more  striking  proof,  perhaps,  is  afforded 
by  the  following  analysis.  This  represents  the  composition  of  a 
specimen,  collected  by  the  writer,  of  the  separated  material  which 
had  caked  on  the  drier.  The  analysis  was  made  by  Mr.  W.  T. 
Schaller,  in  the  laboratory  of  the  United  States  Geological  Survey. 
