Am'/e°bUI:iSarm'}   Vapor- Density  of  Chlorine  and  Ferric  Chloride.  95 
VAPOR-DENSITY  OF  CHLORINE  AND  FERRIC  CHLO- 
RIDE.1 
By  C.  Friedel  and  J.  M.  Crafts. 
The  authors  have  previously  shown  that  the  vapor-density  of  alum- 
inium chloride  is  constant  between  288°,  and  400°,  and  corresponds 
with  the  formula  A12C16.  Deville  and  Troost's  experiments  with  ferric 
chloride  gave  results  corresponding  with  the  formula  Fe2Cl6,  but  the 
later  determinations  of  Y.  Meyer  and  Griinewald  have  shown  that 
between  440°  and  1300°  the  vapor-density  is  always  lower  than  that 
corresponding  with  Fe2Cl6,  and  agrees  more  nearly  with  the  formula 
FeCl3.  There  is  always,  however,  a  want  of  agreement  between  the 
observed  and  calculated  values,  because  at  temperatures  above  518° 
the  ferric  chloride  decomposes  into  ferrous  chloride  and  chlorine.  The 
authors  point  out  that  Meyer's  results  do  not  agree  at  all  well  with  the 
formula  FeCl3,  and  consider  that  above  750°  the  ferric  chloride  dis- 
sociates into  Fe2Cl4  and  Cl2,  whilst  the  further  reduction  of  density 
observed  above  1052°  is  due  to  the  partial  dissociation  of  Fe2Cl4  into 
2FeCl2.  The  boiling  point  of  ferrous  chloride  and  its  vapor-density 
are,  however,  not  yet  known. 
The  modification  of  Dumas'  apparatus  employed  by  the  authors 
makes  it  easy  to  ascertain  whether  dissociation  has  taken  place  and 
any  crystals  have  been  deposited.  They  find  that,  contrary  to  the 
statement  of  Meyer  and  Griinewald,  ferric  chloride  in  an  atmosphere 
of  nitrogen  is  dissociated  into  chlorine  and  ferrous  chloride,  the  latter 
being  deposited  in  almost  colorless  crystals  which  do  not  recombine 
with  the  liberated  chlorine  on  cooling,  nor  after  remaining  in  contact 
with  it  at  the  ordinary  temperature  for  several  days.  The  ferrous 
chloride  is  not  volatile  at  440°,  and  hence  the  volume  of  gas  in  the 
apparatus  is  not  altered  in  consequence  of  the  dissociation. 
In  order  to  prevent  the  dissociation,  the  apparatus  was  filled  with 
chlorine,  and  hence  it  became  necessary  to  determine  the  relative  den- 
sity of  this  gas  at  the  temperatures  employed.  The  chlorine  was  made 
in  some  experiments  from  manganese  peroxide  and  hydrochloric  acid, 
in  others  from  potassium  dichromate  and  hydrochloric  acid,  and  was 
dried  by  means  of  sulphuric  acid.  The  following  results  were 
obtained : — 
Temperature   19' 7°      21*6°      23'0°      356'9°  440'0o 
Sp.  gr   2-479      2  458      2*475       2  451  2*448 
1  Compt.  rend.,  cvii.,  301-306 ;  reprinted  from  Jour.  Chem.  Soc,  1888,  p.  1251. 
