^'FeTi§Tm'}    GM  Chloride  and  Silver  Nitrate  as  Tests.  67 
positively  the  presence  of  cotton-seed  oil ;  there  is,  however,  with 
cotton-seed  oil  always  a  grayish  film  separated  on  the  sides  of  the  test 
tube,  with  mustard  and  rape  oils  a  film  is  formed  which  is  of  a  black 
color,  the  color  being  due  possibly  in  the  first  case  to  metallic  silver,  in 
the  second  case  to  sulphide  of  silver. 
Arachis  oil  with  silver  nitrate  develops  in  a  few  minutes  a  red  color 
which  then  passes  into  a  dark  brown  in  the  course  of  fifteen  minutes ; 
this  test  is  apparently  characteristic  for  arachis  oil  among  the  vegetable 
oils  but  is  also  given  by  some  of  the  fish  oils. 
Cotton-seed  oils  may  differ  in  the  rapidity  with  which  they  react 
with  both  Au  Cl3  and  Ag  NOs,  this  no  doubt  being  due  to  the  manner 
and  completeness  of  the  purification  of  the  oil  by  chemicals  ;  there  is 
also  a  difference  in  their  behavior  to  sulphuric  acid.  To  ascertain 
something  of  the  nature  of  the  body  giving  the  reaction  with  Au  Cl3, 
a  portion  of  cotton-seed  oil  was  mixed  with  alcohol  and  some  pieces  of 
potassium  hydrate ;  after  shaking  a  few  minutes  a  clear  solution  was 
obtained  which  was  poured  off  from  the  undissolved  potassium  hydrate 
into  a  large  volume  of  water ;  by  this  means  the  unsaponified  oil  was 
again  separated,  the  soap  remaining  in  solution ;  the  separated  oil  was 
now  saponified  and  from  the  two  soap  solutions  were  precipitated  the 
fatty  acids.  The  acid  obtained  from  the  easily  saponified  portion  of 
the  oil  contained  a  liquid  and  a  solid  portion  which  could  be  separated 
by  cooling  the  mixture ;  with  Au  Cl3  a  very  fine  red  coloration  was 
produced ;  the  acid  from  the  more  difficultly  saponified  portion  of  the 
oil  was  solid  and  gave  only  a  momentary  red  color,  changing  into  a 
violet  and  depositing  a  dark  precipitate.  The  cause  of  the  red  color 
is  hence  to  be  found  in  the  liquid  acid. 
2.  Commercial  Oils. 
Almond  1  
2  
Arachis  
Lard  1  
"  2  
Mustard  
Olive  1  (green), 
"  2  
"  3  
Poppy-seed.... 
Rape  
Salad  
Au  CI3. 
Red  in  5  minutes. 
No  change. 
Red  in  3  minutes. 
No  change. 
Red  in  3  minutes. 
No  change. 
Red  in  3  minutes. 
"    "  3 
No  change. 
Red  in  3  minutes. 
-Ag  NO3. 
Red  color,  a,  dark ;  b,  very  thick, 
a,  pale  brownish ;  b,  gray  black,  ppe. 
Red  color,  a,  dark ;  b,  brown  black, 
solid. 
a,  no  change;  b,  brownish  black, 
precipitate. 
a,  no  change;  b,  gray  black,  ppe. 
a,  dark,  ppe;  b,  dark  green,  ppe. 
a,  pale  brown ;  b,  dark  red  brown. 
a,  greenish  ;  b,  solid. 
a,  gray  green,  ppe. ;  b,  no  change. 
a,  pale  brown;  b,  pale  yellow,  solid. 
a,  dark  green,  ppe. ;  b,  no  change. 
Red  color,  a,  green,  ppe. ;  b,  gray 
black,  thick. 
