384  Royal  Society :— 
of  the  silver-salt.  A  solution  of  bromine  or  iodine  in  tetrachloride  of 
carbon  was  quickly  decolorized  by  agitation  with  small  particles  of 
argentic  fluoride. 
Crystals  of  boron  did  not  decompose  fluoride  of  silver  at  a  low 
red  heat,  nor  chemically  change  at  60°  Fahr.  an  aqueous  solution  of 
the  salt  containing  either  free  hydrofluoric  or  nitric  acids. 
Vitrified  boracic  acid  violently  decomposed  fluoride  of  silver  in  a 
state  of  fusion,  emitting  copious  white  acid  fumes  ;  but  it  had  no 
chemical  effect  upon  an  aqueous  solution  of  the  salt  at  60°  Fahr. 
By  placing  crystals  of  silicon  upon  argentic  fluoride  in  a  state  of 
fusion,  they  become  at  once  red-hot,  undergoing  rapid  combustion, 
and  evolving  fluoride  of  silicon.  A  lump  of  fused  silicon  slowly  de- 
composed an  aqueous  solution  of  fluoride  of  silver,  setting  free  me- 
tallic silver  in  crystals.  Crystals  of  silver  behaved  similarly,  but 
much  more  rapidly,  and  evolved  abundance  of  gas  if  the  solution 
contained  free  hydrofluoric  acid  ;  on  adding  nitric  acid  to  this  mix- 
ture, bubbles  of  spontaneously  inflammable  silicide  of  hydrogen  gas 
were  evolved  and  ignited. 
Pure  and  dry  precipitated  silica  added  to  fluoride  of  silver,  at  a 
temperature  of  low  redness,  evolved  much  heat,  with  violent  action, 
and  set  free  metallic  silver. 
No  chemical  change  took  place  on  passing  fluoride  of  silicon  over 
red-hot  fluoride  of  silver. 
Argentic  fluoride  in  a  state  of  fusion  is  rapidly  decomposed  by 
sulphur  with  evolution  of  heat ;  fluoride  of  sulphur  is  at  the  same 
time  produced,  and  argentic  sulphide  formed.  To  ascertain  whether 
fluoride  of  sulphur  is  a  gas  or  a  volatile  liquid,  an  apparatus  called 
a  "  gas-collector  "  was  devised  and  employed,  and  a  full  description 
of  its  construction  is  given.  By  using  this  apparatus,  substances 
may  be  heated  without  contact  with  the  external  air,  and  without 
subjecting  the  joints  of  the  apparatus  in  which  they  are  heated  to 
leakage  by  expansion  or  contraction  of  the  gaseous  contents. 
Fluoride  of  sulphur  was  found  to  be  a  heavy  colourless  vapour, 
uncondensable  at  the  temperature  of  melting  ice  and  at  the  or- 
dinary atmospheric  pressure.  It  corrodes  glass,  fumes  strongly  in 
the  air,  and  has  a  characteristic  and  very  powerful  dusty  odour,  not 
very  unlike  that  of  a  mixture  of  chloride  of  sulphur  and  sulphurous 
anhydride.  Sulphur  rapidly  decomposed  an  aqueous  solution  of 
argentic  fluoride. 
Sulphurous  anhydride  passed  over  fluoride  of  silver  at  an  incipient 
red  heat,  produced  little  or  no  decomposition  of  the  silver-salt.  Va- 
porous fluoride  of  sulphur  also  produced  no  visible  effect. 
By  passing  the  vapour  of  liquid  chloride  of  sulphur  over  the  fluo- 
ride in  a  state  of  fusion,  chemical  action  occurred,  a  vapour  was 
evolved  which  corroded  glass  and  possessed  a  dusty  odour,  but  did 
not  condense  to  a  liquid;  it  was  probably  fluoride  of  sulphur.  The 
saline  residue  consisted  of  argentic  chloride  and  sulphide.  A  solu- 
tion of  argentic  fluoride  was  decomposed  by  agitation  with  liquid 
chloride  of  sulphur,  hydrofluoric  acid  being  evolved,  and  argentic 
chloride  and  sulphide  produced. 
