4o6  Assay  of  US. P.  Halogen  Compounds.  {^^^1910"' 
in  the  case  of  chloral)  or  through  a  suitable  combination  of  these. 
The  basis  of  all  these  assays  would  be  the  Volhard  method,  which 
is  already  in  the  U.S. P.,  but  which  is  not  fully  utilized  even  where 
it  is  directly  applicable.  Moreover,  the  Volhard  method  might  be 
applied  to  a  number  of  other  U.S. P.  substances  by  previously 
introducing  halogen  into  them,  as  was  pointed  out  by  the  writer  13 
in  the  case  of  a  large  number  of  the  alkaloids.  It  will  be  seen, 
therefore,  that  while  we  would  thus  supply  methods  of  assay  where 
none  are  given  at  present,  we  would  at  the  same  time  not  in- 
crease the  requirements  for  analytical  skill  on  the  part  of  the 
pharmacist,  but  simply  extend  the  usefulness  of  a  well-known 
method  (the  Volhard  method)  which  is  very  easily  carried  out 
and  which  might  be  made  to  cover  a  very  large  portion  of  the 
U.S.P.  field. 
It  appeared  from  the  literature  examined  that  thymol  iodide, 
(CcH2.CH3.C3H7.OI)2,  is  especially  difficult  to  decompose  by  a 
wet  process  so  as  to  convert  its  halogen  quantitatively  into  in- 
organic (or  readily  ionized)  iodide.  Thus  according  to  Gane  and 
Webster  16  "  none  of  the  usual  wet  methods  is  applicable ;  only 
partial  decomposition  is  effected  by  heating  with  alcoholic  potash 
to  1300  C.  under  pressure,  while  neither  treatment  with  silver 
nitrate  and  nitric  acid  nor  with  freshly  precipitated  silver  chloride 
is  suitable."  Owing  to  this,  "  resort  was  therefore  had  to  fusion 
with  alkali  carbonates."  To  carry  out  such  fusion,  1  Gm.  of  the 
thymol  iodide  is  intimately  mixed  with  an  equal  amount  of 
KNaC4H4Oe  and  5  Gms.  anhydrous  Na2CO:r  A  porcelain  crucible 
of  30  c.c.  capacity  is  used,  and  a  mixture  of  1  Gm.  KNaC4H40(. 
and  5  Gms.  anhydrous  Na2CO:,  is  employed  to  cover  the  mixture 
containing  the  thymol  iodide.  It  is  directed  to  "  heat  to  such 
temperature  as  will  ensure  production  of  a  perfectly  white  fused 
mass  in  forty-five  minutes."  After  cooling,  "  thoroughly  extract 
the  fused  mass  with  water,"  filter,  and  determine  the  halogen  in 
the  filtrate.  As  stated  by  these  authors,  resort  was  had  to  the 
fusion  method  only  after  finding  the  usual  wet  methods  unsuitable. 
Inasmuch,  however,  as  Gane  and  Webster  apparently  had  not 
tried  the  reduction  method,  it  was  thought  desirable  to  make  some 
trials  with  the  latter  method.  The  following  experiments  were 
therefore  carried  out. 
15  Bull.  No.  54,  Hyg.  Lab.,  U.  S.  Pub.  Health  &  Mar.-Hosp.  Serv.,  Wash.. 
and  Jour.  Amcr.  Chem.  Soc,  32,  132-139  (1910). 
16  Drug  Topics,  24,  52-53  (1909). 
