390  Some  Official  and  Non-Official  Iodides.  {Amli^liFis^m' 
first  and  then  heat  the  mixture.  When,  after  sufficient  warming, 
the  bright  yellow  precipitate  has  firmly  subsided,  decant  the  superna- 
tant liquor.  Mix  the  residuary  mercurous  iodide  with  four  to  six  fluid- 
ounces  of  water,  pour  the  mixture  into  a  plain  filter  and  thoroughly 
wash  the  precipitate  with  sufficient  water.  Finally  dry  the  powder 
by  exposure,  but  shielded  from  strong  daylight. 
Bismuih-oxyl  iodide. — The  so-called  sub-iodide  or  oxyiodide  of  bis- 
muth is  attracting  some  attention.  Some  difficulties  are  encountered 
in  the  production  of  a  definite  salt,  having  a  proper  form  and  appear- 
ance. It  has  been  ascertained  that  the  substance  should  have  the  com- 
position BiOI,  and  that  it  should  be  an  amorphous  powder  of  a 
light  brick-red  color.  The  product  usually  obtained,  although  having 
the  desired  physical  character,  is  always  slightly  in  excess  of  the 
theoretical  amount.  The  excess  is  about  sufficient,  in  case  it  were  wa- 
ter, to  give  the  body  the  formula  Bi  01.  Aq,  or  Bi  (OH)2 1.  If  how- 
ever, exposed  to  a  water-bath  heat  for  many  hours,  it  does  not  lose 
appreciably  in  weight.  This,  however,  is  no  serious  evidence  against 
the  presence  of  the  elements  of  water  in  some  state  of  combination. 
But  the  preponderance  of  evidence  seems  to  indicate  that  the 
bismuth-oxyl  nitrate  has  the  formula  Bi  0N03  and  not  Bi  O  NOs  Aq. 
according  to  the  pharmacopoeia.  It  is  officially  stated  to  be  a  heavy,, 
white  powder,  nothing  being  said  about  its  more  intimate  physical 
structure.  When  a  specimen  of  one  of  the  most  reliable  articles  in 
the  market  is  examined  under  a  half-inch  power  it  is  found  to  be 
wholly  made  up  of  stunted  needle-shaped  crystals.  This  condi- 
tion is  also  possessed  by  the  salt  resulting  from  the  writer's  process 
elsewhere  published  in  September,  1884.  The  success  of  this  method 
led  the  writer  to  apply  it  in  the  preparation  of  the  bismuth-oxyl  iodide. 
The  peculiar  feature  of  the  process  consists  in  generating  the  oxy-salt 
in  a  decreasingly  acidine  mixture,  through  the  agency  of  calcium  car- 
bonate. When  a  solution  of  bismuth  nitrate  is  treated  with  potassium 
iodide,  either  in  substance  or  solution,  a  seemingly  black  and  bulky 
bismuth  iodide  is  precipitated.  By  adding  calcium  carbonate  to  a 
mixture  of  one  m.  of  Bi  I3  and  two  ms.  of  Bi  (N03)3  the  brick-red  Bi 
O  I  results  according  to  the  following  equation. 
Bi  I3  +  2  (Bi  (N03)3  +  3  (CaCOs)  =  3  (BiOI)  +  3  (Ca  (M>3)  2  + 
3  C02.  The  presence  of  acetic  acid  exerts  no  solvent  power,  but 
appears  to  be  useful,  if  not  essential  to  the  process.  The  calcium  car- 
bonate is  not  added  to  total  neutrality,  but  merely  in  sufficiency  to 
