AFebSS^fPi9i™'}      Fat  Decomposition  and  Glycerin.  75 
run  in  the  Twitchell  tank  and  thirty-two  inch  (30,000  lbs.)  black 
oil,  cotton-seed  foots  being  handled,  3  per  cent,  of  the  weight  of  the 
charge  of  black  oil  of  Twitchell  reagent  is  added,  steam  turned  into 
the  perforated  coil,  the  trap  door  closed,  and  the  Twitchellman  starts 
his  record  of  that  particular  tank.  First  he  would  ascertain  the 
per  cent,  of  fatty  acid  in  the  black  oil  as  follows : 
The  oil  would  be  put  in  an  Erlenmeyer  and  heated  until  abso- 
lutely dry.  Bluish  vapors  on  the  surface  of  the  oil  indicate  a  dry 
condition.  Fifty  c.c.  alcohol  are  put  into  another  Erlenmeyer  and 
warmed,  4.1  c.c.  of  the  dry  oil  are  run  into  the  50  c.c.  alcohol, 
alkaline  blue  used  as  ian  indicator,  and  half  normal  NaOH  run  in 
until  neutralized.  The  number  of  c.c.  of  NaOH  multiplied  by  4 
gives  the  per  cent,  of  fatty  acid.  The  result  is  noted  in  the  record. 
This  record  must  show  the  number  of  the  tank,  amount  of  charge 
and  class  of  goods,  the  per  cent,  of  fatty  acid  the  goods  contained, 
amount  of  Twitchell  reagent  added,  the  hour  it  started  boiling,  the 
hour  it  stopped  boiling,  the  number  of  hours  of  the  first  boil,  amount 
of  sweet  water  run  off,  and  the  B°  strength  and  per  cent,  of  fatty 
acid  at  end  of  first  boil,  the  hour  of  starting  and  ending  second  boil, 
number  of  hours  boiling,  amount  of  Twitchell  fat  run  off,  and  per 
cent,  of  fatty  acid  at  the  finish.  The  length  of  time  for  the  first 
boil  is  about  thirty  hours  and  should  show  from  87  to  90  per  cent, 
fatty  acid.  After  settling  the  glycerin  water  is  run  off  into  a 
storage  tank,  the  number  of  inches  and  B°  taken.  The  second  boil 
lasts  about  twenty-four  hours ;  no  reagent  is  added  to  the  second 
boil.  A  sample  is  taken  and  should  show  93  to  95  per  cent,  of  fatty 
acid,  it  is  allowed  to  settle  and  is  ready  for  the  distillation  plant. 
The  Twitchell  fatty  acid,  as  the  product  is  now  known,  shows  on 
analysis :  92  to  95  per  cent,  free  fatty  acid ;  4  to  1  per  cent,  unsa- 
ponifiable ;  2  to  3  neutral  fat ;  1  to  y2  per  cent.  dirt. 
When  the  fat  has  thoroughly  settled  it  is  run  into  an  intermediate 
storage  stand  and  then  into  the  "  dry  boxes."  These  dry  boxes 
are  of  cast  iron,  built  up  of  sections  2  ft.  6  in.  square  with  machined 
edges  to  make  a  tight  joint,  the  boxes  are  5  ft.  wide,  5  ft.  deep, 
and  10  ft.  long,  and  when  the  fat  is  drv  and  at  about  275 0  F. 
measure  285  lbs.  per  inch.  Each  box  is  fitted  with  a  closed  brass 
coil  and  connections  to  the  still.  It  is  essential  that  the  fat  be  abso- 
lutely dry  when  fed  into  the  still.  The  distillation  is  carried  on  by 
live  fire,  each  still  being  fitted  with  a  perforated  cross  on  the  bottom 
of  the  inside  of  the  still  through  which  superheated  steam  is  injected. 
A  siow  fire  is^started  under  the  still  and  the  vacuum  pump  started. 
