'^'^NoZ'St^'''^'}    Lard  Adulteration  with  Cotton-Seed  Oil.  575 
The  contents  of  the  bottle  are  poured  into  a  beaker,  the  bottle  is 
rinsed  with  potassium  iodide  solution,  and  the  liquid  titrated  with  tV 
normal  sodium  hyposulphite,  which  has  been  standardized  with  pure 
iodine  just  before  use.  The  Hiibl's  reagent  must  also  be  standardized 
for  each  set  of  experiments,  and  to  offset  the  reducing  action  of  chlo- 
roform upon  the  iodine  solution,  a  quantity  equal  to  that  used  in  the 
test  must  be  added  in  standardizing.  There  is  a  practical  advantage 
in  determining  the  iodine  absorption  of  the  fatty  acids  instead  of  the 
fat,  in  that  the  use  of  chloroform  can  be  dispensed  with,  owing  to  the 
solubility  of  the  fatty  acids  in  alcohol.  The  fatty  acids  are  best  pre- 
pared by  saponifying  the  fat  with  rectified  spirit  and  the  saturated 
aqueous  solution  of  caustic  soda,  recommended  by  Wollny  for  use  in 
Reichert's  butter  process. 
8.  Silver  nitrate  test. — This  test  is  considered  by  all  to  be  charac- 
teristic for  cotton-seed  oil ;  in  its  execution  various  methods  are  em- 
ployed. I.  Bechi^s  test^  contains  an  amylic  alcohol  solution  of  rape 
oil,  which  it  has  been  shown  can  be  dispensed  with  without  impairing 
the  delicacy  of  the  test.  The  simplified  reagent  is  a  solution  of  1  gm. 
silver  nitrate  in  200  gm.  alcohol  and  40  gm.  ether,  acidifying  by  ad- 
dition of  0.1  nitric  acid.  To  the  oil  or  fat  to  be  examined  add  half 
its  bulk  of  the  above  solution  and  heat  in  a  water-bath  for  fifteen 
minutes.  Pure  lards  always  remain  perfectly  unchanged,  cotton-seed 
oil  mixtures  blacken  more  or  less  quickly.  II.  Milliau^s^  modification 
of  the  above.  III.  Stock's  process  is- based  on  that  of  Milliau.  15 
gm.  of  the  sample  are  saponified  in  a  7-inch  capsule  with  a  mixture  of 
15  cc.  of  a  30  per  cent.  NaOH  solution,  and  15  cc.  92  per  cent,  al- 
cohol by  heating  the  fat  to  110°  C.  and  adding  the  mixture,  1  cc.  at  a 
time,  with  constant  stirring.  The  temperature  should  not  fall  below 
95°  C. ;  if  the  operation  has  been  successful,  the  soap  is  a  smooth, 
thick  paste.  Boiling  distilled  water  is  added  slowly  at  first  until  the 
paste  is  thinned,  then  water  is  added  to  make  500  cc,  in  which  vol- 
ume the  soap  should  dissolve  completely.  40  cc.  dilute  SO4  (1-10) 
are  added  and  the  liquid  brought  to  a  boil  for  7  to  12  minutes,  then  kept 
just  below  boiling,  until  the  separated  fatty  acids  fuse  to  a  clear,  oily 
layer  from  which  the  greater  part  of  the  aqueous  layer  is  removed  by 
syphonage;  the  remainder  with  the  fatty  acids  is  poured  into  a  clean, 
warm  flask  with  a  long  and  narrow  neck.    The  acids  are  freed  as 
1  American  Journal  of  Pharmacy,  1887,  280. 
2  American  Journal  of  Pharmacy,  1888,  290. 
