6 10  Separation  of  Resin  from  Fatty  Acids.  {Amv™*\m&rva' 
holic  solution,  the  acids  constituting  resin  are  not  attacked.  The 
process  obviously  may  be  either  gravimetric  or  volumetric,  but 
chemists  will  prefer  the  latter  on  account  both  of  speed  and  accu- 
racy. The  description  of  the  process  is  as  follows : — 2-5  to  3  grms. 
of  the  dried  fatty  and  resin  acids  are  dissolved  in  from  25-30  cc. 
of  perfectly  absolute  alcohol,  and  a  current  of  dry  hydrochloric  acid 
gas  passed  in  constantly.  The  flask  containing  the  mixture  must 
be  kept  cool  by  immersion  in  cold  water.  When  the  etherification 
is  complete  the  ethers  separate  and  the  gas  is  no  longer  absorbed. 
The  flask  is  removed,  corked  well,  and  allowed  to  stand  half  an 
hour.  It  is  diluted  with  about  1 00  to  125  cc.  hot  water,  then 
cooled,  transferred  to  a  separatory  funnel,  and  agitated  with  75  cc.  of 
ether.  The  watery  layer  is  removed,  and  the  ethereal  layer  washed 
with  cold  water  till  neutral  to  delicate  litmus  solution  (twice  always  is 
sufficient).  The  ethereal  liquid  is  received  in  a  flask,  the  separator 
washed  out  with  about  50  cc.  of  neutral  spirit,  and  the  whole 
titrated  by  standard  alcoholic  alkali,  using  phenolphthalein  as  indi- 
cator. The  alkali  should  be  standardized  by  an  accurate  solution 
of  half  normal  HC1,  and  should  be  either  one-fifth  or  one-half 
normal  according  to  the  amount  of  resin  in  the  fatty  acids.  Taking 
the  mean  combining  weight  of  resin  as  347,  then  the  percentage  is 
easily  calculated ;  it  is  reported  both  on  100  of  dry  fatty  matter  and 
on  100  of  soap. 
Twitchell's  test  experiments  are  eminently  satisfactory,  and  I 
have  now  pleasure  in  confirming  them  by  my  own  tests  : 
(1)  Sample  of  distilled  fatty  acids  containing  no  resin,  when 
treated  as  described  showed  0-7  per  cent,  resin. 
(2)  The  above  distilled  fatty  acids,  to  which  were  added  common 
resin  to  the  extent  of  22-5  per  cent.,  showed,  when  treated  as  above 
described,  23-3  per  cent,  of  resin,  which,  after  deducting  the  07  per 
cent,  found  in  No.  I,  gives  exactly  22-5  per  cent.,  or  the  amount 
which  was  added. 
(3)  Soap  made  from  palm  oil  and  other  fats,  but  no  resin,  gave 
0  8  per  cent,  resin. 
(4)  Another  soap  made  from  fatty  matter  of  unknown  origin,  but 
no  resin,  gave  i-O  per  cent,  resin.  This,  it  should  be  observed, 
was  of  a  dark  color,  and  evidently  contained  some  altered  or  oxi- 
dized oily  matter. 
(5)  Soap  which  showed  by  Gladding's  test  6  per  cent,  of  resin, 
gave  4-9  per  cent,  by  Twitchell's  process. 
