Am'reb.!i£7arm"}  Testing  of  Balsams,  Resins  and  Gum  Resins.  91 
THE  TESTING  OF  BALSAMS,  RESINS  AND  GUM 
RESINS. 
Dieterich  and,  more  recently,  A.  Kremel  have  attempted  to  extend 
the  Kottstorfer  method  of  examining  fats  and  oils  to  the  testing  of 
substances  included  in  the  groups  of  balsams,  resins  and  gum  resins. 
The  leading  idea  in  Kottstorfer's  method,  it  will  be  remembered,  is 
that  in  fats  and  oils,  besides  free  fat  acids,  there  are  present  glycerin 
ethers  of  fat  acids.  By  titration  it  is  ascertained  how  much  potassium 
hydrate  is  required  by  a  unit  of  the  fat  or  oil  to  combine  with  the  free 
acid,  and,  further,  how  much  is  used  up  in  the  saponification  of  the 
glycerin  ether.  The  former  quantity  is  distinguished  as  the  acid 
number,  the  latter  as  the  ether  number,  and  the  sum  of  the  two  as  the 
saponification  number.  Quite  similar  data  are  yielded  by  balsams, 
resins  and  gum  resins,  as  all  these  substances  contain  free  acids  mixed 
with  varieties  of  ethers. 
The  determination  of  these  bodies  may,  therefore,  be  carried  out  in 
a  manner  quite  analogous  to  the  Kottstorfer  method.  About  one 
gm.  of  the  substance  to  be  examined  is  dissolved  in  alcohol  free  from 
acid  reaction,  some  drops  of  phenolphthalein  added  and  then  titrated 
with  half-normal  potash  solution  until  there  is  a  permanent  red  colora- 
tion. The  quantity  of  caustic  potash  used  for  one  gm.  of  the  sub- 
stance is  taken  in  milligrams,  and  this  is  called  the  acid  number.  In 
those  substances  where  ether  is  present  in  addition  to  acid,  a  definite 
portion  of  the  liquid  is  heated  with  excess  of  half-normal  potash  solu- 
tion, and  then  titrated  back  with  hydrochloric  acid.  The  quantity  of 
alkali  used  is  calculated  to  one  gm.  of  the  substance,  and  the  number 
of  the  milligrams  similarly  taken  as  the  ether  number.  The  sum  of 
the  two  gives  the  saponification  number. 
In  the  examination  of  substances  not  completely  soluble  in  alcohol 
they  are  dissolved  with  the  aid  of  ether-alcohol  or  ether-chloroform. 
Gum  resins  are  first  exhausted  in  a  Soxhlet  apparatus  with  alcohol, 
and  the  alcoholic  extract,  after  drying  and  weighing,  is  estimated  ;  the 
numbers  obtained  are  not  calculated  in  respect  to  the  whole  of  the 
substance  originally  taken,  but  only  for  the  quantity  of  resin  soluble 
in  alcohol.  In  the  determination  of  light-colored  substances  the  use 
of  phenolphthalein  presents  no  difficulty ;  with  dark-colored  sub- 
stances, such  as  [Peru  balsam,  guaiacum  resin,  etc.,  the  difficulty  is 
overcome  by  adding  water  to  the  alcoholic  solution  up  to  the  point  of 
milky  turbidity,  and  then  dropping  in  alternately  potash  solution, 
