'ttS'SI  dssay  of  US.P.  Halogen  Compounds.  407 
GENERAL  MODE  OF  PROCEDURE. 
As  a  result  of  some  preliminary  experiments,  it  was  found  that 
the  following-  procedure  yielded  satisfactory  results :  The  thymol 
iodide 17  (0.1  to  0.5  Gm.)  was  treated,  in  a  500  c.c.  Erlenmeyer 
flask,  with  10  c.c.  of  ether  (U.S. P.),  followed  by  20  c.c.  of 
approximately  ^  alcoholic 18  sodium  hydroxide  and  2  Gms.  zinc 
dust,19  mixing  thoroughly  after  adding-  each  of  these  constituents. 
The  contents  of  the  flask  were  then  actively  boiled  under  a  reflux 
condenser  for  one  hour.  The  flask  was  then  disconnected  from 
the  condenser  and  the  contents  acidified  with  10  c.c.  of  glacial 
acetic  acid  (99.5  per  cent.  )  and  diluted  with  200  c.c.  of  distilled 
water,  mixing  thoroughly  after  adding  each  of  these  constituents. 
The  contents  of  the  flask  were  then  again  actively  boiled  under  the 
reflux  condenser  for  another  hour.  (With  this  procedure  there 
is  the  fortunate  circumstance  that  the  undissolved  residue  tends  to 
conglomerate,  while  the  liquid  finally  becomes  perfectly  clear  and 
hence  filters  very  rapidly.)  The  condenser  was  then  washed  with 
a  small  amount  (about  10  c.c.)  of  water  which  was  allowed  to 
drain  into  the  flask  and  the  contents  of  the  latter  filtered  (using 
about  30  c.c.  of  hot  water  in  the  washings).  The  filtrate  then 
received  a  measured  amount  of  AgNOs  which  was  a  little 
(about  5  c.c.)  in  excess  of  that  theoretically  required.  The  whole 
was  then  actively  boiled  for  ten  minutes,  50  c.c.  of  dilute  (10  per 
cent. )  nitric  acid  added,  and  again  actively  boiled  for  five  minutes. 
After  filtering  (using  about  30  c.c.  of  hot  water  in  the  washings) 
and  cooling  to  room-temperature,  the  excess  silver  in  the  filtrate 
was  determined  by  means  of  standard  thiocyanate,  using  5  c.c. 
of  10  per  cent,  ferric  alum  as  indicator. 
In  applying  the  above  method  to  assaying  thymol  iodide,  it 
should  also  be  possible  to  determine  any  considerable  amount  of 
chlorine,  if  present,  by  weighing  the  silver  precipitate  and  finding 
the  amount  of  chlorine  by  calculation  as  pointed  out  by  Gane  and 
Webster.20 
In  order  to  determine  the  effect  of  varying  the  time  of  the 
11  The  thymol  iodide  used  in  this  work  was  obtained  from  a  well-known  firm 
whose  products  usually  are  of  a  high  degree  of  purity. 
18  Prepared  by  dissolving  20  Gms.  of  NaOH  in  40  c.c.  water  and  making  up 
to  1000  c.c.  with  alcohol  (U.S. P.). 
19  As  zinc  dust  frequently  contains  small  amounts  of  chlorine  suitable  controls 
were  made  in  all  cases. 
20Loc.  cit. 
