AmMaTCh;wo9nn'}'  Scammony  Resin.  109 
so  dark  that  it  was  impossible  to  see  the  end  point  with  much  accu- 
racy when  so  dilute  a  solution  was  used  for  titration.  The  quantity 
of  indicator  (which  was  the  customarily  employed  phenolphthalein) 
had  to  be  larger  than  ordinary,  not  being  less  than  10  drops.  Find- 
ing that  the  N/5  solution  used  did  not  work  so  well  as  could  be 
desired,  recourse  was  had  to  N/2  alcoholic  potash.  With  this  the 
determinations  were  finally  carried  out  with  a  greater  degree  of 
accuracy,  at  least  in  the  observation  of  the  quantity  of  solution  used 
for  titration.  There  was,  of  course,  a  consequent  loss  in  accuracy 
through  the  use  of  the  more  concentrated  solution,  but  this  was  more 
than  compensated  by  the  facts  just  mentioned;  so  that  for  all 
practical  purposes  the  use  of  the  N/2  alcoholic  potash  will  be  found 
preferable  to  a  more  dilute  solution  for  use  with  this  resin. 
From  the  results  obtained  it  appears  that  the  acid  value  de- 
termination is  of  no  importance  in  the  distinguishing  between  true 
and  false  scammony  resin.  The  lowest  values  found  concord  with 
the  acid  value  of  resin  scammony  recorded  by  Kremel  as  quoted  by 
Dieterich  (Analysis  of  Resins,  218),  which  was  14.6.  The  acid 
values  as  a  whole  show  no  wider  variation  than  might  be  expected 
in  samples  of  resin  obtained  entirely  from  true  scammony  root.  The 
results  obtained  by  Cowie  are  somewhat  higher  for  genuine  scam- 
mony and  lower  for  Mexican  scammony. 
Saponification  Value. — For  the  determination  of  the  saponifica- 
tion value  1.5  grammes  of  the  resin  were  treated  with  25  c.c.  of  N/2 
alcoholic  potash  and  boiled  gently  for  half  an  hour  under  a  reflux 
condenser.  In  attempting  then  to  determine  the  excess  of  the  alkali 
by  titration  with  N/2  hydrochloric  acid  it  was  found  that  with  any 
reasonable  amount  of  phenolphthalein  it  was  in  many  cases  absolutely 
impossible  to  see  the  end  reaction.  Furthermore,  an  additional  diffi- 
culty arose  in  that  in  some  cases  the  resin-soap  produced  was  de- 
posited in  the  bottom  of  the  flask  as  a  sticky  mass  which  was 
insoluble  in  alcohol  and  all  the  other  usual  organic  solvents  and 
which  occluded  a  considerable  quantity  of  alkali.  This  rendered  the  . 
end  point  indecisive  as,  after  titrating  to  the  disappearance  of  the 
red  color  of  the  phenolphthalein,  when  such  disappearance  could  be 
observed,  on  standing,  the  solution  again  became  alkaline  from  the 
dissolving  of  some  of  the  occluded  alkali.  This  is  not  a  case  of 
alkalinity  produced  by  the  hydrolysis  of  the  resin-soap  through  the 
presence  of  the  water  introduced  as  N/2  hydrochloric  acid,  but  is 
truly  a  case  of  occlusion.    The  difficulty  of  seeing  the  end  point 
