ACTION  OF  IODIDE  OF  STARCH  ON  VARIOUS  SALTS.  223 
chlorine  water,  over  and  above  what  may  be  necessary  to  pre- 
cipitate the  oxide  of  iron,  etc.,  then  the  liquid  being  filtered, 
and  then  slowly  heated  to  expel  the  excess  of  ammonia,  or 
neutralized  by  adding  nitric  acid.  By  adding  a  solution  of 
ferrocyanate  of  potassa,  a  red  precipitate  will  be  formed,  or  at 
least  it  will  show  a  red  color,  according  to  the  greater  or  less 
quantity  of  copper  contained  in  the  liquid.  If  it  be  desired  to 
ascertain  the  exact  quantity  of  copper,  then  sulphuretted  hydro- 
gen gas  must  be  passed  through  the  chlorine  water,  the  sulphu- 
ret  of  copper  thus  formed  must  be  decomposed  and  oxidized  by 
using  nitro-muriatic  acid,  and  the  copper  is  to  be  precipitated 
from  the  filtered  solution  by  caustic  potassa.  The  oxide  of 
copper  now  obtained,  must  be  edulcorated,  exsiccated,  ignited 
and  weighed. 
According  to  my  judgment,  the  Edinburgh  formula  for  mak- 
ing chlorine  water  should  be  expunged  from  the  Dispensatory  of 
the  United  States,  and  apothecaries  should  only  be  allowed  to 
prepare  the  article  according  to  the  Dublin  method.  Sapienti 
sat! 
ON  THE  ACTION  OF  IODIDE  OF  STARCH  ON  VARIOUS  SALTS. 
By  M.  F.  Pisani. 
Iodide  of  starch  poured  into  solutions  of  various  salts,  is  de- 
colored in  certain  cases,  whereas  in  others  its  blue  color  is  un- 
affected. Thus,  the  salts  of  silver  immediately  decolor  iodide 
of  starch,  but  those  of  lead  and  copper  have  no  action  on  it.  The 
metals,  besides  silver,  which  produce  this  decoloration  are — mer- 
cury, tin  (stannous  salts,)  antimony  (the  chlorides,)  arsenic 
(arsenious  acid  and  chloride,  As  CI3,)  gold  (perchloride,)  iron 
(ferruginous  salts,)  and  manganese  (manganic  salts.) 
Iodide  of  starch  enables  us  at  once  to  dis'tinguish  the  mercu- 
rous  from  the  mercuric  salts ;  for  with  the  mercurous  salts,  there 
is  decoloration,  at  the  same  time  that  the  yellow  iodide  is  pre- 
cipitated, whereas  with  the  mercuric  salts  there  is  decoloration 
without  the  formation  of  any  precipitate. 
Stannous  and  stannic  salts,  likewise  behave  quite  differently 
with  this  reagent.  Thus,  the  first  alone  have  the  property  of 
causing  it  to  lose  its  color.    Arsenious  acid  and  its  correspond- 
