124  CHEMICAL  CONSTITUTION  OF  FLUORINE  COMPOUNDS,  ETC. 
ON  THE  CHEMICAL  CONSTITUTION  OF  FLUORINE  COM- 
POUNDS, AND  ON  THE  ISOLATION  OF  FLUORINE. 
By  M.  Prat. 
The  following  is  a  full  abstract  of  M.  Prat's  memoir  on  this 
subject,  recently  communicated  to  the  French  Academy.  The 
complete  paper  will  not  be  published  until  the  chemical  referees 
of  the  Academy  have  reported  on  it. 
M.  Prat  considers  that  chemists  have  hitherto  been  mistaken 
as  to  the  composition  of  fluorides  and  the  theory  of  fluorine.  He 
regards  the  fluorides  as  in  reality  oxyfluorides,  and  the  equiva- 
lent of  fluorine  as  consequently  much  higher  than  is  usually  sup- 
posed.   He  represents  fluoride  of  calcium  by 
2  equivalents  of  calcium,  .  .  .  40*0 
1  "  oxygen,  .  .  .  8-0 
1  "  the  new  fluorine,         .  .  29-6 
77-6 
This  accords  with  the  known  analyses  of  fluor  spar,  since  it 
contains  51*5  per  cent,  of  calcium. 
By  doubling  the  old  equivalent  of  fluorine  (19)  we  get  38,  that 
is  to  say  nearly  the  sum  of  the  equivalents  of  oxygen  (8),  and  of 
the  new  fluorine  (29-6)=37-6. 
According  to  M.  Prat,  in  order  to  obtain  true  fluorine  it  suf- 
fices to  heat  fluoride  of  calcium  with  chlorate,  or  rather  with  per- 
chlorate  of  potash,  since  it  is  only  after  the  formation  of  this 
latter  salt  that  the  reaction  takes  phice.  Oxygen  is  disengaged 
and  also  a  product  which  silver  absorbs.  The  compound  so 
formed  is  fluoride  of  silver,  insoluble  in  water,  soluble  in  ammo- 
nia, from  which  it  is  precipitated  by  nitric  acid,  and  more  rap- 
idly altered  in  the  light  than  chloride  of  silver.  Neither  chlo- 
rine nor  oxygen  attack  it  even  at  the  fusing  point  of  the  fluoride. 
It  is,  however,  decomposed  by  potash  at  a  dull  red  heat,  and  this 
reaction  permits  its  analysis  :  it  contains — 
Silver,       .       .    0-785    .       .    108-0—1  equivalent. 
Fluorine,   .       .  -0-215    .       .      29-6  " 
Fluoride  of  silver,  1-000 
This  fluoride  of  silver,  insoluble 
and 
137-6 
very  stable,  and  having 
