Am.  Jour.  Pharm. 
Jan.,  1887. 
Bismuth  Subiodide. 
11 
varying  chemical  composition,  if  any  of  the  details  of  preparation  are 
deviated  from  in  the  slightest  degree. 
In  the  first  place,  if  the  acid  solution  of  the  bismuth  salt  is  too  acid 
and  the  potassium  iodide  solution  is  too  strong,  iodine  is  liberated  and 
the  product  is  black,  probably,  from  the  formation  of  the  black  trio- 
dide  (Bi  Is)  of  Messrs.  Fletcher  and  Cooper.1  Then,  if  the  acid  solu- 
tion is  too  weak  or  the  added  potassium  iodide  is  too  dilute,  the  great 
tendency  is  toward  the  formation  of  a  large  proportion  of  oxynitrate. 
Then,  if  to  the  strongly  acid  solution  the  iodide,  in  not  sufficiently 
diluted  solution,  is  added  the  precipitate  will  be  very  deep  reddish- 
brown  in  color,  which  apparently  does  not  change  on  standing  in  cold 
water,  and  the  variability  of  whose  hue  seems,  partially  at  least,  to  de- 
pend upon  the  acidity  of  the  acid  solution  and  upon  the  temperature  at 
which  the  liquids  are  mixed.  Lastly,  if  the  acid  solution  is  made 
with  the  correct  degree  of  acidity  and  is  poured  into  mixed  solution 
of  potassium  iodide  and  sodium  acetate,  the  so-called  yellow  iodide  of 
bismuth  is  formed;  a  precipitate  whose  color  varies  in  shade  as  ob- 
tained by  different  methods,  and  whose  contained  iodine,  in  quantity, 
is  in  direct  proportion  to  the  depth  of  its  color.  This  latter  product 
has  been  proved1  to  be  nothing  more  than  a,  very  basic  compound  of 
five  molecules  of  bismuthous  oxide  (Bi2  03)  and  one  molecule  of  bis- 
muth iodide  (Bi  I3). 
The  extreme  variability  of  the  products  sold  as  pure  bismuth  sub- 
iodide  may  be  inferred  from  the  fact,  that  of  the  several  makes  which 
have  appeared  in  the  markets,  one  was  of  a  light-buff  yellow  color, 
apparently  made  as  previously  mentioned  or  by  trituration,  simply,  of 
the  oxynitrate  with  a  solution  of  potassium  iodide.  Another  was 
very  light  reddish-yellow  in  color,  evidently  made  by  trituration  of 
the  oxynitrate  with  Lugol's  solution  of  iodine,  and  consisting  of  a 
slightly  larger  percentage  of  oxyiodide  than  the  former ;  and,  yet  another 
sample  was  of  the  normal  brick-red  color  characterizing  the  true  pro- 
duct. 
The  first  process  devised  by  the  author  was  used  for  nearly  two 
months,  and  was  based  upon  the  fact  that  bismuth  subnitrate  was  first 
decomposed,  partially,  when  triturated  with  potassium  iodide,  in  aque- 
ous solution,  to  form  small  quantities  of  iodide  and  oxide  of  bismuth, 
then  by  nascent  iodine  (in  the  presence  of  hot  water),  liberated  through 
1  Year-book  of  Pharmacy,  1882,  p.  472-479. 
