124  IMPROVEMENTS  IN  TREATING  FATTY  AND  OILY  MATTERS. 
same  state  of  intimate  mixture  in  which  they  enter  them.  I 
therefore  prefer  to  place  the  series  of  heating  tubes  in  a  vertical 
position,  so  that  any  partial  separation  which  may  take  place 
while  the  liquids  pass  up  one  tube,  may  be  counteracted  as  they 
pass  down  the  next.  I  believe  that  it  will  be  found  useful  to  fix 
at  intervals  in  the  heating  tubes  of  such  apparatus  as  may  admit 
of  such  an  addition,  diaphragms  pierced  with  numerous  small 
holes,  so  that  the  liquids  being  forced  through  these  obstructions 
may  be  thoroughly  mixed  together.  I  deem  it  prudent  to  test 
the  strength  of  the  apparatus  by  a  pressure  of  10,000  lbs.  to  the 
square  inch  before  taking  it  into  use  :  but  I  believe  that  the  work- 
ing pressure  necessary  for  producing  the  heat  I  have  mentioned, 
will  not  be  found  to  exceed  2000  lbs.  to  the  square  inch.  When 
it  is  desired  to  diminish  the  contact  of  the  liquids  with  iron,  the 
tube  or  channels  of  the  apparatus  may  be  lined  with  copper. 
The  hot  mixture  of  fat  acids  and  solution  of  glycerin  which 
escapes  from  the  exit  valve  of  the  apparatus  are  separated  from 
each  other  by  subsidence ;  the  fat  acids  may  then  be  washed  with 
water,  and  the  solution  of  glycerin  concentrated  and  purified  by 
the  usual  means. 
The  fat  acids  thus  produced  may,  like  those  obtained  by  other 
methods,  be  used  in  the  manufacture  of  candles  and  soap,  and 
applied  to  various  purposes  according  to  their  quality ;  and  when 
desired  they  may  also  be  first  bleached  or  purified  by  distillation 
or  otherwise,  as  is  now  well  understood. 
I  prefer  that  the  fatty  bodies  should  be  previously  deprived,  as 
far  as  practicable,  of  such  impurities  as  would  cause  the  discolora- 
tion of  the  fat  acids  produced ;  but  when  the  fat  acids  are  to  be 
finally  purified  by  distillation,  this  preliminary  purification  is  of 
less  importance. 
When  any  acid  or  other  corrosive  agent  shall  have  been  used 
for  purifying,  hardening  or  otherwise  preparing  the  fatty  body 
to  be  operated  upon,  I  take  care  that  all  traces  of  it  shall  be 
washed  out  or  neutralized  before  passing  it  through  the  apparatus. 
Some  fatty  bodies  (particularly  when  impure)  generate  during 
the  process,  a  portion  of  acetic  or  other  soluble  acid,  which  might 
tend  to  injure  the  iron  tubes  ;  in  such  cases  I  add  a  correspond- 
ing quantity  of  alkaline  or  basic  matter  to  the  water  and  oil 
before  they  are  pumped  into  the  tubes. 
