142 
ON  A  NEW  TEST  FOR  IODIDES. 
of  the  importance  of  the  matter  and  the  fact  that  I  have  myself 
verified  the  accuracy  of  the  process  by  repeated  trials,  to  make 
it  public. 
Brewer's  process  was  founded  upon  the  hypothesis,  confirmed 
as  above  by  Pereira  and  myself,  that  the  iron  is  in  the  form  of 
protochloride,  and  consists  simply  of  a  conversion  of  this  proto- 
chloride  into  sesquichloride  by  passing  a  few  bubbles  of  chlorine 
gas  through  a  nearly  saturated  hot  solution  of  crude  sal-am- 
moniac, and  the  subsequent  decomposition  of  the  sesquichloride  of 
iron  by  ammonia.  The  solution  is  then  kept  hot  on  the  sand  bath 
for  a  short  time,  or  until  the  precipitate  separates  in  flocks,  and 
then  quickly  filtered  while  hot.  On  cooling,  the  sal-ammoniac 
ci^stallizes  out  absolutely  pure. 
When  passing  the  chlorine  gas  into  the  liquid,  special  care 
must  be  taken  to  keep  the  liquid  hot,  and  not  to  prolong  the  ac- 
tion sufficiently  to  allow  the  formation  of  the  well  known  danger- 
ously explosive  compound  Nil  CI2,*  usually  called  chloride  of 
nitrogen.  It  is  evident  that  the  sal-ammoniac  obtained  cannot 
contain  any  free  chlorine,  all  the  chlorine  introduced  being  con- 
verted into  chlorohydric  acid,  which  combines  with  the  excess  of 
ammonia,  or  according  to  the  long  known  reaction, 
4  NIP  +  3  01  =  3  Nil4  CI  +  N. 
ON  A  NEW  TEST  FOR  IODIDES. 
By  David  S.Price,  Ph.  D.,  F.  C.  S. 
Having  in  the  preceding  paperf  pointed  out  the  principle  on 
which  the  detection  of  nitrites  by  means  of  iodide  of  potassium 
and  hydrochloric  acid  depends,  I  shall  proceed  briefly  to  describe 
the  application  of  nitrites  for  the  detection  of  iodides,  and  at  the 
same  time  give  one  or  two  instances  of  the  practical  application 
of  the  test  in  cases  where  the  quantity  of  iodine  is  exceedingly 
small. 
The  method  of  employing  the  test  is  the  following.  The  liquid 
*The  discovery  by  Adolphe  Wurtz,  of  the  detonating  compound  formed 
by  the  action  of  chlorine  upon  ethylamine,  and  called  by  him  "  V eihylamine 
bichloree,"  (Mcmoire  sur  les  ammoniaques  composees,  par  M.  Ad.  Wurtz,  p. 
o3)  leaves  us  hardly  any  alternative,  if  we  consider  the  perfect  analogy  be- 
tween the  two  cases,  than  to  assign  the  above  formula  to  the  soi-disant  chlo- 
ride of  nitrogen.  N 
fSee  Chem,  Gazette  vol.  ix.  p.  290. 
