442 
AiKiliitlcdl  ]le<:'(ir(']t('s  (lii'l  Inrc-Hiuidiion,^.  | 
Am.  Jour,  rhiirm. 
Sept..  1882. 
ANALYTICAL  RESEARCHES  AND  INVESTIGATIONS, 
Collated  by  Pkof.  Frkdkrick  B.  Powek,  Ph.D. 
Estimation  of  Resin  joitli  Fats.  By  T.  S.  Gladding. — The  autlior 
recomnieiids  the  following  method  for  the  quantitative  estimation  or" 
resin,  when  accompanied  by  fats,  which  is  based  upon  the  insolubility 
in  ether  of  the  silver  salts  of  the  fatty  acids,  while  the  resinate  of  sil- 
ver is  readily  dissolved  in  large  amounts;  a  small  amount  of  alcohol 
which  may  be  contained  in  the  ether  exerts  no  objectionable  intluenc*^ 
About  0*5  gram  of  the  fatty  acids  containing  resin  is  brought  into  a 
small  flask,  20  cul)ic  ceutimeters  of  95  per  cent,  alcoliol  added,  and  the 
mixture  shaken  until  the  fatty  acids  and  resin  are  dissolved.  One  drop 
of  a  phenolphtalein  solution  is  then  added,  and  subsequently  a  satura- 
ted alcoholic  solution  of  potassa,  drop  by  drop,  with  constant  agitation, 
until  the  red  coloration  which  designates  the  excess  of  alkali  becomes 
permanent.  One  or  two  drops  of  the  potassa  solution  are  afterwards 
added  in  excess,  the  mixture  maintained  at  the  temperature  of  boiling 
alcohol  for  ten  minutes  upon  the  water-bath,  in  order  to  ensure  the 
complete  saponification  of  the  fat;  after  being  allowed  to  cool  the  con- 
tents of  the  flask  ai'c  Avashed  by  means  of  concentrated  ether  into  a 
graduated  cylinder,  holding  100  cubic  centimeters,  which  is  afterAvards 
filled  with  ether.  The  contents  of  the  cylinder  are  mixed  by  agitation^ 
one  gram  of  very  finely  powdered  neutral  nitrate  of  silver  added,  and 
the  whole  actively  shaken  for  10  or  15  minutes,  until  the  flocculeut 
precipitate  of  stearate  and  oleate  of  silver  has  aggregated  and  i)ecome' 
deposited,  whereupon  from  50  to  70  cubic  centimeters  of  the  clear 
liquid,  filtered,  if  necessary,  are  brought  into  a  second  graduated  cylin- 
der of  the  capacity  of  100  cubic  centimeters.  To  this  liquid  a  small 
additional  amount  of  nitrate  of  silver  is  added  in  order  to  determine 
Avhether  the  fatty  acids  have  been  c;ompletely  precipitated,  in  wliich 
case  the  liquid  will  remain  clear.  20  cubic  centimeters  of  a  mixture  of 
one  part  of  hydrochloric  acid  and  two  parts  of  water  are  then  added^ 
and  actively  agitated,  whereby  the  complete  decomposition  of  all  tin; 
silver  salt  is  accomplished,  and  after  being  allowed  to  subside  a  definite 
amount  of  the  supernatant  etherial  resin,  solution  is  separated,  and 
evaporated  in  a  platinum  capsule  on  the  water-bath  to  dryness.  Tlu;- 
residue  is  then  weighed,  and  consists  of  the  resin,  which  can  contain  at- 
the  most  only  traces  of  accompanying  oleic  acid. 
The  utility  of  the  described  method  has  been  tested  by  the  author 
