^ptemberTilS!'}  Assay  °f  U.S. P.  Halogen  Compounds.  405 
dust  under  a  reflux  condenser,  the  zinc  dust  being  replaceable  by 
zinc  filings  and  acetic  acid/ or  by  aluminium  powder  and  acetic 
acid,  the  time  required  for  effecting  the  decomposition  of  the 
chloral  in  Self's  procedure  being  only  from  twenty  to  thirty 
minutes. 
In  this  connection  it  seemed  to  the  writer  that  having  such 
excellent  methods  for  estimating  chloral  and  chloroform,  it  would 
be  desirable  that  the  U.  S.  Pharmacopoeia  (which  at  present  gives 
no  method  whatever  for  estimating  the  percentage  purity  of  these 
substances,  although  in  the  case  of  chloroform  it  prescribes  a 
purity  of  99  to  99.4  per  cent.)  should  include,  in  the  next  revision, 
methods  of  assay  based  on  these  principles.  Such  want  should  be 
filled  not  only  for  the  sake  of  consistency  and  completeness,  but 
also  because  there  is  actual  demand  for  such  methods,  as  may  be 
seen  from  the  fact  that  the  British  Pharmacopoeia  had  included  a 
method  for  assaying  chloral  hydrate  even  before  either  Wallis  or 
Self  described  their  improved  (chloride)  methods  and  although 
the  B.P.  procedure,  as  already  mentioned  above,  was  shown  by 
Hinrichs  to  be  very  far  from  satisfactory.  Similarly,  Gane  and 
Webster  12  cite  a  controversy  with  one  of  the  large  users  of  iodo- 
form as  showing  the  importance  of  establishing  a  standard  method 
of  assay  for  this  substance  and  point  out  that  Utz's  13  method  might 
be  used,  wherein  the  iodine  of  the  iodoform  is  converted  into 
silver  iodide  and  the  excess  silver  nitrate  determined  volumetrically. 
Likewise,  in  the  case  of  bromoform  (for  which  the  present  U.S. P. 
prescribes  a  purity  of  99  per  cent,  without,  however,  giving  any 
method  of  assay),  Richaud 14  has  pointed  out  how  its  bromine 
can  be  readily  converted  into  bromide  and  the  bromoform  thus 
estimated  through  a  determination  of  the  resulting  bromide.  In 
other  words,  there  appears  no  sufficient  reason  why  a  number  of 
the  halogen-containing  substances  of  the  U.S. P.  should  remain 
without  any  method  of  assay  when  it  is  quite  probable  that  every 
one  of  them  could  be  very  readily  estimated  through  a  determina- 
tion of  its  halogen.  Further,  it  is  quite  probable  that  the  con- 
version of  the  organic  halogen  into  inorganic  halide  can  be  effected 
in  all  cases  by  some  modification  of  the  alkaline  or  of  the  reduction 
method  (typified  by  the  Wallis  and  Self  procedures,  respectively, 
aPharm.  Jour.,  (4),  28,  555  (1909). 
nApoth.  Zeit  (Berlin),  18,  869  (1903). 
"'Tour,  de  pharm.  et  de  chim.,  (6),  9,  232-236  (1899),  and  Tour.  Chem.  Soc, 
76,  (2),  527  (1899)- 
