270  ARSENIOUS  ACID  AND  IODIDE  OF  POTASSIUM. 
Distilled  water  or  rain-water  600  litres. 
Pyrophosphate  of  soda  5  kilogrms. 
Dried  and  fused  tin-salt  1  kilogrm. 
Chemical  Gazette,  from  Le  Technologiste,  18 5 1,  p.  629. 
ON  THE  COMPOUNDS  OF  ARSENIOUS  ACID  WITH  IODIDE  OF 
POTASSIUM. 
By  E.  Harms. 
Emmet  has  stated  that  a  solution  of  arsenite  of  potash,  mixed 
with  sufficient  acetic  acid  to  prevent  reddening  of  turmeric- 
paper,  gives  rise  to  a  pulverulent  precipitate  of  the  composition 
KI,  3  AsO3,  on  the  addition  of  iodide  of  potassium.  The  author  has 
tested  this  statement,  and  found  that  this  salt  contains  water, 
which  is  not  dispelled  at  302°  F.  The  quantity  of  potassium 
found  amounted  to  8-21. 
In  these  experiments  the  author  has  also  discovered  two  other 
salts  of  the  same  kind.  One  of  these  is  produced  when  arsenite 
of  potash  is  employed  without  neutralization  by  acetic  acid,  the 
precipitate  formed  on  the  addition  of  iodide  of  potassium  dissolved 
in  boiling  water,  the  solution  mixed  with  8  or  4  vols,  of  hot 
alcohol,  and  then  treated  with  carbonic  acid  gas  until  a  film  of  salt 
begins  to  be  formed  upon  the  sides  of  the  vessel,  and  upon  the 
tube  through  which  the  gas  is  passed.  A  syrupous  fluid  sepa- 
rates, containing  much  carbonic  acid  with  iodine  and  arsenious 
acid.  If  the  alcoholic  solution  be  then  further  evaporated,  a 
finely  crystalline  compound  is  obtained,  with  the  composition 
KI+3(KO  HO,  AsO3).    Its  analysis  gave,— 
KI  .  .  26-06  25-98  1  26-32 
AsO3  .  .  46-91  46-87  3  47-01 
KO  .  .  21-35  21-15  3  1  22-39 
HO  .  .  5.43  4-67  3  4-28 
The  3  equivs.  of  water  are  not  driven  off  at  212°  F.,  and 
even  at  526°  F.  the  water  was  not  expelled. 
The  salt  is  readily  soluble  in  water  and  alcohol.  The  hot 
saturated  solution  deposits  the  following  salt  on  cooling,  in  wart- 
like masses,  in  which  no  appearance  of  crystallization  can  be 
detected  even  under  the  microscope. 
With  the  salts  of  the  alkaline  earths,  earths  and  metallic  oxides, 
