^'"sfp^'^im*""  }     Analytical  E&mrrches  and  In/vedigafiom.  443 
with  mixtures  of  resin  and  fjitty  acids  in  known  proportions,  and  has 
proved  perfectly  satisfactory.  It  is  particularly  adapted  for  the 
technical  examination  of  soap,  to  which  resin  is  frequently  added,  and 
in  this  (;ase  the  previous  separation  of  the  fatty  acids  may  be  avoided  by 
dissolving  the  scraped  soap  directly  in  alcohol,  and  proceeding  as  above 
described.— P/i arm.  Zeitung,  No.  49,  1882,  p.  361,  from  Chem.  News,. 
Detection  of  Salicylic  Acid  in  Foods. — This  is  usually  accomplished 
by  agitating  the  substance  to  be  examined  with  ether,  benzol  or  carbon 
bisulphide.  The  method  is,  however,  circumstantial,  and  is  not  appli- 
cable in  the  presence  of  fats.  The  following  simple  and  reliable 
method,  perfected  in  the  laboratory  of  the  "  Chemiker-Zeitung,^^  is 
based  upon  the  volatility  of  salicylic  acid  with  aqueous  vapor.  If  a 
liquid,  wine,  beer,  milk,  etc.,  is  to  be  examined,  about  100  cubic  cen- 
timeters of  the  same  are  brought  into  a  flask  connected  with  a  Liebig's 
condenser,  and  distilled  as  quickly  as  possible.  A  few  drops  of  the 
distillate  are  collected  from  time  to  time,  and  tested  with  pure,  neutral 
ferric  chloride  ;  if  a  violet  coloration  ensues,  salicylic  acid  is  present. 
From  dilute  solutions  the  salicylic  acid  does  not  distil  so  readily  as 
from  concentrated.  A  liquid,  e.  g.,  which  contained  0*005  per  cent,  of 
salicylic  acid  gave  in  the  first  half  of  the  distillate  only  a  very  feeble 
reaction,  while  two  drops  of  the  following  portion  assumed  with  ferric 
chloride  an  intense  violet  color.  Salicylic  acid  is  not  volatile  with 
alcohol  vapors,  and  likewise  not  in  the  presence  of  tannin  ;  in  the  lat- 
ter case,  and  when  contained  in  red  wine,  it  suffices  to  acidulate  with, 
sulphuric  acid  in  order  to  obtain  perceptible  amounts  of  salicylic  acid 
in  the  distillate. 
If  non-volatile  substances,  such  as  butter,  are  to  be  examined  a  suf- 
ficient amount  is  brought  into  a  flask,  an  active  current  of  steam  led 
through  the  mass,  and  the  distillate  tested  as  above.  With  slight 
traces  of  salicylic  acid  which  are  no  longer  detectable  in  the  distillate 
by  ferric  chloride  (O'OOOd  gram  dissolved  in  100  cubic  centimeters  of 
water  yields  an  intense  coloration),  a  large  amount  of  the  distillate  is 
slightly  supersaturated  with  ammonia,  and  evaporated  on  the  watei- 
bath  to  dryness.  The  residue  is  then  dissolved  in  a  little  water,  and 
tested  with  ferric  (chloride  ;  if  the  violet  coloration  does  not  now 
appear  the  absence^  of  salicylic  acid  is  proven. 
It  is  still  to  be  observed  that  the  violet  (coloration  does  not  ap])ear  in 
the  presence  of  free  acids,  alkalies,  or  large  amounts  of  salts. —  Cliem, 
Zeitung,  No.  32,  1882,  p.  619. 
