PREPARATION  OF  SOAP  FOR  SOAP  LINIMENT. 
269 
alkali  together  until  they  unite,  the  oil  be  first  treated  in  the 
cold  with  2Dth  of  its  weight  of  strong  sulphuric  acid  and  allowed 
to  remain  for  twenty-four  hours,  it  is  rendered  so  soluble  in  liq. 
sodae  that  its  conversion  into  soap  becomes  a  matter  of  the 
utmost  facility.  Adopting  this  plan,  I  have  found  the  process 
to  be  one  of  the  easiest  of  pharmaceutical  operations.  The  acid 
mixes  freely  with  the  oil,  forming  a  blackish-colored  fluid.  On 
the  addition  of  the  soda  this  color  entirely  disappears,  and  the 
soap  obtained  is  quite  white.  The  follow^ing  is  the  method  of 
procedure  I  have  found  to  be  the  most  convenient : — 
Almond  oil  IJ  pound  (av.), 
Sulphuric  acid  1  ounce  (weight), 
Liq.  sodse  10  pints  (Imp.) 
Add  the  acid  to  the  oil,  stirring  the  mixture.    Allow  this  to 
remain  for  twenty-four  hours.    Then  pour  it  into  the  liq.  sodse 
contained   in   a  clean  iron  vessel,    and  apply   heat.  Very 
shortly  after  it  boils,  the  liquid  becomes  perfectly  bright  and 
transparent ;  the  fire  is  then  removed,  and  the  whole  allowed  to 
become  perfectly  cold.    The  soap  is  then  found  as  a  coherent 
cake  floating  on  the  top  of  the  liquor.    It  is  laid  on  a  calico  fil- 
ter, and  left  to  drain  for  several  hours  ;  or,  if  it  is  desired  to 
obtain  it  perfectly  free  from  all  traces  of  caustic  alkali,  it  may 
be  redissolvcd  in  10  pints  of  boiling  water,  and  a  strong  solution 
of  5  oz.  of  common  salt  added.    As  the  mixture  cools,  the  soap 
rises  to  the  surface ;  and  when  quite  cold,  again  forms  a  fine 
layer,  resting  on  the  aqueous  liquid.    No  loss  of  weight  is  thus 
incurred.    The  soap  is  placed  on  calico  to  drain,  after  which  it 
may  be  submitted  to  moderate  pressure,  or  melted  in  a  tared 
dish,  and  reduced  to  a  uniform  weight  of  2i  pounds.  When 
thoroughly  cold,  it  forms  a  firm  white  soap,  which  may  be  cut 
into  pieces,  and  kept  for  use  in  a  covered  pot. 
In  the  preparation  of  linimentum  saponis,  this  soap  is  mace- 
rated in  the  spirit  in  the  cold.  It  very  quickly  dissolves,  es- 
pecially if  the  mixture  be  agitated.  From  4  to  5  per  cent,  of 
the  weight  of  the  soap  remains  insoluble,  as  a  flocculent  deposit. 
After  this  is  filtered  out,  a  pale  liniment  is  obtained,  which  may 
be  kept  at  32°  F.  for  any  length  of  time  without  thickening  or 
depositing.    The  Pharmacopoeia  does  not  direct  the  soap  to  be 
