436         FATTY  ACIDS  FOR  CANDLE  AND  SOAP  MAKING. 
fatty  acids  obtained  is  96 — 97  per  cent.  The  operation  is 
carried  out  in  a  single  day ;  thus,  operating  on  2000  kilo- 
grammes, three  hours  are  required  for  the  saponification,  one 
hour  for  the  decomposition,  three  hours  for  the  fusion  and  set- 
tling, for  the  crystallization  eight  hours,  for  pressure  when 
cold  in  a  double  press  four  hours,  making  altogther  nineteen 
hours  for  the  operation ;  and  as  the  crystallization  takes  place 
in  the  night,  there  is  in  effect  only  eleven  hours'  work. 
By  this  simple  method  we  effect  not  only  great  economy  in 
labor,  fuel  and  product,  but  also,  thanks  to  the  lowness  of  the 
temperature  throughout,  we  obtain  an  inodorous,  unaltered 
stearic  acid,  fusible  at  58° — 59°,  and  an  oleic  acid,  equal,  if 
not  superior,  to  the  best  oils  used  in  soap  making. 
It  is  obvious  that  this  manufacture  is  revolutionized.  Fatty 
bodies  are  now  treated  to  produce  stearic  acid,  leaving  oleic 
acid  as  residue ;  in  future,  the  same  fatty  bodies  will  be  treated 
to  obtain  oleic  acid,  and  the  price  of  stearic  acid  will  be  low- 
ered by  the  value  of  the  oleic  acid  obtained. 
Thus  M.  Ohevreul's  prognostications  will  be  realized,  and 
the  products  of  France,  where  this  manufacture  originated,  will 
no  longer  be  inferior  to  those  of  foreign  countries. 
Soaps. — The  best  white  soap  may  be  made  from  pure  oleic  acid, 
either  alone  or  mixed  with  other  oils.  None  but  neutral  oils 
can  be  used,  such,  for  instance,  as  are  now  used  for  Marseilles 
soap.  In  the  first  case — that  is  to  say,  when  oleic  acid  only 
is  used,  the  glycerine  being  removed — it  suffices  to  saturate 
this  acid  by  a  feeble  washing.  The  soap  globules  form  imme- 
diately, and  no  delay  is  required  before  fusing  them.  On  the 
contrary,  when  oleic  acid  is  mixed  with  other  oils,  or  when 
only  neutral  oils  are  employed,  the  process  described  for  suet 
is  used.  The  fatty  bodies  are  converted  into  the  globular  state, 
the  globules  being  kept  in  motion  by  a  hot  and  salt  lixivium 
until  complete  saponification.  The  saponified  globules  are  se- 
parated by  fusion,  the  soap  is  melted,  separated  from  the  lixi- 
vium, and  poured  into  the  moulds  where  it  solidifies  by  cooling. 
The  operation  requires  six  hours'  effective  work,  and  in  twenty- 
four  hours  a  soap  is  obtained  as  perfect  as  neutral,  and  lathery 
as  old  Marseilles  soap.  (The  specimens  of  silk  presented  to 
the  Academy  had  been  comparatively  treated  at  the  Gobelins 
