NEW  TEST  FOR  THE  PURITY  OF  CHLOROFORM.  149 
colored  by  these  salts.  The  sensitiveness  of  the  reagent  is  so 
great  that  a  thousandth  of  alcohol,  wood-spirit  or  ether,  in  the 
chloroform,  can  be  readily  detected.  Roussin  has  experimented 
with  different  specimens  of  the  chloroform  of  commerce  and 
found  a  percentage  of  alcohol  in  some  truly  fabulous  ;  and  in 
others,  which  gave  but  a  very  slight  opalescence  after  being 
agitated  with  water,  the  nitro-sulphides  produced  a  color  almost 
black. 
The  test  is  easily  applied,  by  introducing  the  chloroform  into 
a  tube  closed  at  one  end,  then  adding  a  few  centigrammes  of 
the  nitro-sulphides  and  shaking  the  contents  of  the  tube.  It 
is  allowed  then  to  rest  for  a  few  minutes.  The  chloroform  if 
pure  will  remain  as  limpid  as  distilled  water  :  but  if  it  contain 
alcohol,  ether  or  wood-spirit,  it  assumes  a  dark  color,  varying 
with  the  percentage  of  these  foreign  substances,  but  which  is 
appreciable  even  when  as  small  an  amount  as  a  thousandth  is 
present. 
To  prepare  the  nitro-sulphide  of  iron,  it  is  only  necessary  to 
mix  two  solutions, — one  of  nitrate  of  potassa  and  the  other  of 
sulphydrate  of  ammonia,  and  adding,  drop  by  drop,  to  this  mix- 
ture a  solution  of  proto  sulphate  of  iron,  constant  stirring  being 
employed,  until  the  mixture  retains  but  a  slight  alkaline  reac- 
tion. It  is  then  raised  to  the  boiling  point,  and  is  evaporated 
to  dryness  over  a  water  bath.  The  residuum  is  treated  with 
alcoholized  ether  and  thrown  on  a  filter.  By  evaporation  of  this 
liquid,  prismatic  crystals  of  the  binitrosulphide  of  iron  are  ob- 
tained which  should  be  washed  with  weak  liquor  ammoniac.  The 
product  is  then  dried  in  the  air  on  some  folds  of  absorbent 
paper,  and  preserved  in  a  flask  with  a  ground  stopper. 
This  body  may  be  considered  as  a  compound  of  sulphide  of 
iron,  sulphydric  acid  and  binoxide  of  nitrogen.  Its  formula  is 
-FeS,  N02  +  Fe2  S3,  N02+  HS.  It  resembles  the  double  cy- 
anides of  iron  by  its  chemical  behavior,  and  the  latent  state  of 
the  molecules  of  iron,  the  nitrpprussiates  by  the  similarity  in  for- 
mation, and  a  grouping  so  analogous  that  it  is  possible  to  pass 
from  one  series  to  the  other  by  a  simple  substitution — Journal 
and  Trans,  of  the  Maryland  Col.  of  Phar. 
