74  Fat  Decomposition  and  Glycerin.  {AFetaXy,Pi9iom' 
of  fatty  acids  in  petroleum  ether  onto  a  filter  and  filter  into  a  tared 
dish,  add  more  ether  to  the  water,  thoroughly  washing  Erlenmeyer 
and  separatory  funnel,  each  time  pouring  the  ethereal  washings 
onto  filter.  Finally  wash  filter  and  funnel  stem.  You  now  have  the 
total  fatty  acids  in  a  petroleum  ether  solution  in  a  tared  dish.  Dry 
until  the  loss  is  not  more  than  0.02  grammes  in  20  min.  at  ioo°  C. 
Before  the  pump  was  started  six  to  nine  inches  of  water  was  turned 
into  the  decomposing  tank  and  the  steam  turned  on,  an  open  coil 
being  fitted  in  the  tank.  (The  water  is  only  used  in  starting  a  new 
plant,  thereafter  the  decomposing  tank  will  contain  an  indefinite 
amount  of  waste  acid  from  the  rest  of  the  plant.) 
Cotton-seed  foots  are  50  per  cent,  saponified  when  received  and 
are  "  decomposed  "  into  "  black  oil  "  by  boiling  with  sulphuric  acid. 
When  there  is  waste  acid  in  the  decomposing  tanks  it  is  started 
boiling  the  same  time  the  car  is  being  emptie'd  so  that  the  saponifica- 
tion is  broken  up  almost  as  fast  as  it  can  be  pumped.  After  boiling 
an  hour  it  is  tested  by  allowing  same  to  run  off  a  paddle  and  should 
show  no  trace  of  soap.  It  is  allowed  to  settle,  the  water  and  dirt 
going  to  the  sewer.  (If  the  first  boil  has  been  on  waste  acid  the 
acid  is  exhausted  when  it  tastes  salty.)  After  running  the  settlings 
into  the  sewer  add  about  three  inches  of  water  and  1  per  cent,  of 
sulphuric  acid  and  boil  until  fat  is  brilliant  and  clear.  Allow  to 
settle.  This  is  waste  acid,  tastes  sour,  and  does  for  the  first  boil 
on  the  next  car.  After  settling  "  skim  "  the  oil  from  the  top  with 
a  gravity  suction  pipe  into  "  black  oil  storage  tank."  From  storage 
the  clear  black  oil  is  run  into  "  acid  boil  tank  "  and  shows  a  varying 
analysis :  dry  black  oil ;  50  to  75  per  cent,  fatty  acid ;  2  to  4  per  cent, 
unsaponified ;  4  to  2  per  cent,  glycerin ;  1  to  2  per  cent,  moisture ; 
y2  to  iJ/2  per  cent,  dirt 
In  the  acid  boil  tank  1  per  cent,  of  sulphuric  acid  and  just  enough 
water  to  cover  the  coil  are  added.  The  precaution  here  is  that  the 
waste  acid  should  be  180  B,  for  cotton-seed  foots,  to  obtain  a  good 
product;  this  waste  acid  goes  to  the  decomposing  tanks.  The  fat 
is  boiled  in  the  acid  boil  tank  for  about  two  hours,  a  sample  taken 
for  analysis  and  the  stock  is  ready  for  the  Twitchell  tank. 
It  requires  a  man  of  intelligence  somewhat  above  the  average 
unskilled  employee  to  be  "  Twitchellman."  He  does  the  "  rough 
analysis  "  of  the  tanks  during  operation  and  keeps  the  records  of 
each  tank.  Where  there  are  so  many  tanks  it  is  practically  impos- 
sible to  weigh  each  charge,  so  that  the  tanks  are  measured  and 
weight  of  contents  per  inch  calculated.    Six  inches  of  water  are 
