IMPROVEMENTS  IN  TREATING  FATTY  AND  OILY  MATTERS.  123 
mixture  which  has  been  operated  upon  to  escape  out  of  the  cool- 
ing tubes,  h,  h,  at  the  valve,  i,  placed  at  the  other  end  of  the 
apparatus.  No  steam  or  air  should  be  allowed  to  accumulate  in 
the  tubes,  which  should  be  kept  entirely  full  of  the  mixture.  For 
this  purpose,  whenever  it  may  be  required,  the  speed  of  the  pump 
should  be  increased,  so  that  the  current  through  the  tubes  may 
be  made  sufficiently  rapid  to  carry  out  with  it  any  air  remaining 
in  them.  Although  the  decomposition  of  the  neutral  fats  by 
water  takes  place  with  great  quickness  at  the  proper  heat,  yet  I 
prefer  that  the  pump,  c9  should  be  worked  at  such  a  rate  in  pro- 
portion to  the  length  or  capacity  of  the  heating  tubes,  d,  d,  d, 
that  the  mixture  while  flowing  through  them  should  be  maintained 
at  the  desired  temperature  for  about  ten  minutes  before  it  passes 
into  the  refrigerator  or  cooling  parts,  h,  h,  of  the  apparatus. 
The  melting  point  of  lead  has  been  mentioned  as  the  proper 
heat  to  be  used  in  this  operation,  because  it  has  been  found  to 
give  good  results ;  but  the  change  of  fatty  matters  into  fat  acids 
and  glycerin  takes  place  with  some  materials  (such  as  palm  oil) 
at  the  melting  point  of  bismuth,  yet  the  heat  has  been  carried 
considerably  above  the  melting  point  of  lead  without  any  appar- 
ent injury,  and  the  decomposing  action  of  the  water  becomes 
more  powerful  as  the  heat  is  increased.  By  starting  the  appara- 
tus at  a  low  heat  and  gradually  increasing  it,  the  temperature 
giving  products  most  suitable  to  the  intended  application  of  the 
fatty  body  employed,  can  easily  be  determined. 
To  indicate  the  temperature  of  the  tubes,  d,  d,  d,  I  have  found 
the  successive  melting  of  metals  and  other  substances  of  different 
and  known  degrees  of  fusibility  to  be  convenient  in  practice. 
Several  holes,  half  an  inch  in  diameter  and  two  or  three  inches 
deep,  are  bored  into  the  solid  parts  of  the  casting  surrounding. the 
tubes,  each  hole  being  charged  with  a  different  substance.  The 
series  I  have  used  consist  of  tin,  melted  at  about  440°,  bismuth 
at  about  510°,  lead  at  about  612°,  and  nitrate  of  potash  at  about 
660°.  A  straight  piece  of  iron  wire  passing  through  the  side  of 
the  furnace  to  the  bottom  of  each  of  the  holes,  enables  the  work- 
man to  feel  which  of  the  substances  are  melted,  and  to.  regulate 
the  fire  accordingly.  It  is  important  for  the  quickness  and  per- 
fection of  the  decomposition  that  the  oil  and  water  during  their 
entire  passage  through  the  heating  tubes  should  remain  in  the 
