Am.  Jour.  Pharm.  1 
July,  1910.  J 
Analysis  of  Ointments. 
319 
Soap. — If  an  ointment^  is  mixed  in  a  separating  funnel  with 
about  three  times  its  volume  of  ether  and  shaken  with  water,  the 
latter  will  take  up  the  soap.  On  addition  of  diluted  hydrochloric 
acid  to  the  aqueous  solution  a  turbidity  and  separation  of  the  fatty 
acids  will  take  place.  Instead  of  mixing  with  ether  the  ointment 
may  be  agitated  with  hot  water,  filtered  after  standing  for  about 
one  hour  and  acidulated  with  hydrochloric  acid  as  before. 
Soaps  insoluble  in  water  (oleates,  lead  plaster)  are  decomposed 
on  shaking  with  hot  diluted  hydrochloric  acid,  the  latter  dissolving 
the  metal. 
Free  Fatty  Acids. — Stearic  Acid. — These  can  be  detected  by 
treating  the  ointment  with  alcohol,  filtering  and  adding  an  alcoholic 
solution  of  lead  acetate.  A  white  precipitate  indicates  the  presence 
of  a  fatty  acid.  Resin  and  soap,  however,  give  a  similar  reaction. 
One  can  also  resort  to  the  following  test 1  for  stearic  acid :  Melt  a 
small  quantity  of  the  material  in  a  porcelain  dish,  stir  up  the  melted 
substance  for  a  few  moments  with  ammonia  water  and  allow  to 
cool.  Remove  the  solidified  mass  from  the  surface,  or  filter  through 
a  wetted  filter  and  acidulate  the  liquid  with  hydrochloric  acid,  when 
stearic  acid  will  be  precipitated. 
Stearic  acid  when  heated  with  alkali  carbonates  on  the  water 
bath  forms  salts  with  effervescence,  giving  off  C02. 
Stearic  acid  has  a  high  acid  number,  200-210,  its  admixture  with 
fats,  oils  and  paraffin  may  be  suspected  on  finding  a  high  acid  num- 
ber, when  colophony,  which  also  has  a  high  acid  number,  is  absent. 
Resinous  Substances. — Colophony,  turpentine,  etc.  (see  under 
substances  soluble  in  alcohol).  The  presence  of  colophony  can  be 
detected  by  the  following  method,  which  was  originally  given  in  a 
somewhat  different  form  by  Parry  for  the  detection  of  colophony 
in  shellac.2  The  colophony  is  isolated  from  the  ointment  by  shaking 
a  small  amount  of  the  latter  with  hot  strong  alcohol,  separating  the 
alcoholic  solution  after  cooling  by  filtration  and  pouring  the  filtrate 
in  water.  The  precipitate  is  collected  on  a  filter,  dried,  triturated 
with  petroleum  ether  and  filtered.  If  no  precipitate  forms  and  the 
liquid  has  the  appearance  of  an  emulsion,  it  should  be  evaporated 
to  dryness  on  the  water  bath  and  the  recovered  colophony  triturated 
with  petroleum  ether  as  before.  On  shaking  the  filtrate  with  a  very 
dilute  copper  acetate  solution,  the  petroleum  ether  will  be  colored 
emerald  green  in  the  presence  of  colophony. 
Another  color  reaction  for  colophony  has  been  given  by  Sans,3  as 
