72  Fat  Decomposition  and  Glycerin.      { ^b^im™' 
trade,  and  is  being  more  extensively  used  by  the  soap  manufacturers 
who  have  recognized  the  advantages  of  the  process  for  the  recovery 
of  glycerin,  in  that  95  per  cent,  of  all  the  glycerin  in  the  fat  can 
be  obtained  as  CP.  This  will  give  yields  from :  good  tallow, 
9  to  10  per  cent,  absolute  glycerin  ;  cocoanut  oil,  12  to  13  per  cent, 
absolute  glycerin  ;  cotton  oil,  10  per  cent,  absolute  glycerin  approx. ; 
grease  and  poor  tallow,  6  to  8  per  cent,  absolute  glycerin. 
The  sweet  water  to  be  evaporated  contains  15  per  cent,  glycerin 
instead  of  from  2  to  4  per  cent,  as  in  spent  lye,  and  therefore  about 
25  per  cent,  as  much  water  has  to  be  evaporated  to  make  crude 
glycerin  as  with  soap  lye.    As  an  illustration : 
The  glycerin  refiner  is  supposed  to  obtain  9  per  cent,  of  absolute 
glycerin  by  weight ;  of  the  total  amount  of  tallow  saponified,  actually 
about  yy2  per  cent,  is  obtained ;  as  the  tallow  contained  approxi- 
mately 10  per  cent,  of  glycerin  the  loss  is  considerable.  Instead  of 
having  to  handle  200,000  lbs.  of  spent  lye  containing  3.75  to  4.25 
per  cent,  of  glycerin,  by  the  Twitchell  process  of  first  deglycerizing 
the  fats  there  would  be  approximately  60,000  lbs.  of  sweet  water 
containing  15  per  cent,  of  glycerin.  Besides  having  to  handle  such 
a  large  quantity,  the  spent  lye  contains  salt,  alkali,  and  fats,  which 
are  troublesome  to  remove ;  the  Twitchell  sweet  water  only  has  to 
be  neutralized  with  lime  before  concentrating,  consequently  there 
is  a  reduction  in  loss  of  glycerin  to  almost  nothing  and  a  product 
of  crude  glycerin  containing  90  per  cent,  of  absolute  glycerin 
against  80  from  soap  lye,  which  means  a  less  expense  in  the  refinery. 
The  Twitchell  crude  is  of  better  quality,  containing  but  a  few  tenths 
of  one  per  cent,  of  ash  and  CP.  can  be  made  in  one  distillation, 
while  it  often  requires  three  distillations  from  soap  lye  crude,  so 
that  a  still  will  handle  about  30  per  cent,  more  per  hour  of  the 
Twitchell  crude  and  produce  less  glycerin  foots. 
The  fatty  acid  obtained  can  be  saponified  with  soda  ash  instead 
of  caustic,  which  means  a  net  saving  of  12  cents  per  hundred 
pounds  of  fat  saponified,  and  finally  the  fatty  acid  is  of  much  better 
odor  than  the  original  stock. 
In  some  cases  it  is  of  more  importance  to  obtain  good  color 
fatty  acid  than  high  yield  of  glycerin,  and  for  working  convenience 
the  stock  is  divided  into  three  classes : 
First.  No.  1  tallow,  mutton  tallow,  yellow  or  white  cotton  oil, 
cocoanut  and  palm  kernel  oil,  white  grease,  olive  oil,  corn  oil,  lard, 
and  good  stearin.    The  color  and  odor  are  of  prime  importance. 
Second.  No.  1  and  No.  2  tallow  and  "  off  "  cotton  oil,  all  the 
