Am.  Jour.  Pharm. 
April,  19 1 9. 
Estimation  of  Phenacetin. 
243 
for  calculating  the  results,  owing  to  the  difficulty  of  determining 
when  an  excess  has  been  added,  and  it  is  therefore  necessary  to  de- 
termine .the  amount  of  quinone  chlorimine  formed,  after  addition 
of  excess  of  hypochlorite  and  removal  of  free  chlorine  from  solu- 
tion. In  the  absence  of  free  chlorine,  the  reaction  between  the 
quinone  compound  and  hydriodic  acid  affords  a  convenient  means 
of  determining  this.  The  reaction  is  the  reverse  of  that  given 
above,  four  atoms  of  iodine  being  liberated  by  each  molecule  of 
quinone  chlorimime,  and  /?-aminophenol  being  re-formed. 
As  no  reagent  was  found  which  will  combine  with  the  excess  of 
free  chlorine  without  also  decomposing  the  chlorimine,  and  boiling 
is  out  of  the  question  owing  to  the  volatility  and  instability  of  the 
latter  in  hot  solutions,  the  chlorine  must  be  removed  by  blowing  a 
current  of  air  through  the  solution.  Experiments  showed  that 
chlorine  is  fairly  rapidly  removed  by  this  means,  100  Cc.  of  a 
saturated  aqueous  solution  of  this  gas  losing  98  per  cent,  of  its 
strength  after  five  minutes  aeration  at  the  rate  of  700  to  800  Cc. 
of  air  per  minute,  and  becoming  practically  free  from  chlorine  after 
fifteen  minutes.  The  quinone  chlorimine  being  also  slightly  vola- 
tile, and  tending  to  decompose  on  long  standing  in  acid  solution,  it 
is  necessary  to  add  a  small  correction  to  account  for  this.  Any 
error  introduced  by  the  action  of  the  dissolved  air  on  the  iodide 
subsequently  added  is  included  in  this  correction,  which  averages 
1  : 5  per  cent,  of  the  total  quinone  chlorimine  present  for  an  aera- 
tion of  from  fifteen  to  twrenty  minutes. 
The  details  of  the  method  finally  adopted  are  shown  in  the  fol- 
lowing examples  of  its  application : 
Estimated  of  p- Amino  phenol,  p-Phenetidine,  etc. — An  amount 
of  an  acid  solution  equivalent  to  about  0.1  Gm.  of  the  base  is 
measured  into  a  250  Cc.  stoppered  bottle  and  diluted  to  rather  more 
than  100  Cc. ;  5  Cc.  of  strong  hydrochloric  acid  are  added,  followed 
by  10  Cc.  of  sodium  hypochlorite  solution  (about  0.8  N).  The 
resulting  solution  should  be  pure  yellow,  and  not  deposit  yellow 
flocks.  Air  is  now  blown  through  at  a  brisk  rate  for  fifteen  minutes, 
in  which  time  all  chlorine  will  have  been  removed,  2.5  Gm.  of  potas- 
sium iodide  are  added,  and  the  solution  allowed  to  stand  for  at  least 
five  minutes,  as  the  reduction  is  rather  slow.  The  liberated  iodine 
is  then  titrated  with  N fio  thiosulphate  and  starch  indicator.  Any 
residual  blue  tint  shows  that  reduction  has  not  been  complete. 
Each  Cc.  of  N /10  thiosulphate  is  equivalent  to  0.00273  Gm.  of 
