336     ROSANILIN  A  REAGENT  FOR  FREE  FATTY  ACIDS,  ETC. 
ON  ROSANILIN  AS  A  REAGENT  FOR  FREE  FATTY  ACIDS, 
AND  FOR  COD-LIVER  OIL. 
By  Dr.  F.  Jacobsen. 
The  author  finds  that  rosanilin  is  insoluble  in  neutral  fatty- 
oils,  but  is  at  once  colored  pale  red,  more  or  less  deep,  if  the 
oil  is  rancid,  or  has  any  free  oily  acid  present,  and  if  very  ran- 
cid, as  deep  as  gooseberry  juice.  The  fuchsin  of  commerce  (mu- 
riate, arseniate,  &c,  of  rosanilin)  dissolves  in  neither  neutral  or 
rancid  oils,  or  fat  acids.  Oleic  acid  and  all  the  fatty  acids  dis- 
solve rosanilin  immediately  in  great  quantity,  and  are  deeply 
colored.  The  oleate  of  rosanilin  dissolves  in  all  proportions  in 
the  oils  and  neutral  fats.  The  rosanilin,  for  this  reason,  can  be 
employed  to  detect  free  acid  in  mixtures  of  oils. 
The  author  proposes  this  reagent  as  a  means  of  detecting  the 
so-called  bleached  cod-liver  oil  sold  in  the  European  markets, 
-which  is  not  cod-liver  oil,  but  the  oily  fats  of  different  marine 
mammals,  or  those  oils  prepared  by  shaking  with  potash  lye, 
and  allowed  to  stand  till  clarified.  As  the  medical  properties  of 
cod-liver  oil  should  be  partly  attributed  to  the  free  fat  acids  that 
it  contains,  the  white  oil  thus  prepared  possesses  properties  analo- 
gous to  the  neutral  fish  oils,  and,  unless  rancid,  are  not  colored 
by  anilin. 
In  some  lubricating  oils  oleic  acid  residues  have  been  used  as 
an  adulteration,  which  this  test  will  easily  discover. 
When  an  oil  contains  but  very  little  free  acid,  the  test  should 
be  applied  as  a  saturated  solution  of  rosanilin  in  absolute  alco- 
hol,— a  few  drops  added  to  the  oil,  and  heated  in  a  water-bath 
with  stirring  until  the  alcohol  is  evaporated.  If  no  free  fatty- 
acid  is  present  no  coloration  is  produced,  and  the  test  separates, 
and  is  deposited  at  the  bottom  of  the  vessel,  or  remains  in  sus- 
pension as  a  brownish  powder. 
Specimens  of  Provence  oil  and  oil  of  sweet  almonds  did  not 
color ;  oil  of  poppy  seed  slightly  red ;  linseed  oil  deeply  red, 
modified  by  the  yellow  color  of  the  oil ;  castor  oil  colors  yet  more 
decidedly.  Olive  oil,  mixed  with  five  per  cent,  of  oleic  acid,  is 
tinted  like  gooseberry  juice.— -Jour,  de  Chim.  Med.,  from  Neues 
Jahr.fur  Pharm. 
