530       ACTION  OF  PHOSPHATE  OF  SODA  ON  FLUOR  SPAR. 
It  was  calculated  that  2NaO,  P05  +  NaO,  C02  +  3CaF  would 
produce  3CaO,  P05  +  3NaF. 
Accordingly  the  ordinary  phosphate  was  converted  into  the 
pyrophosphate  at  a  red  heat,  and  after  the  mixture  of  the  differ- 
ent substances,  heat  was  carefully  applied  to  expel  the  carbonic 
acid,  and,  afterwards,  to  melt  the  mass,  which  wants  frequent 
stirring  with  a  clay  rod.  After  cooling  on  an  iron  plate,  the 
mass  contained  crystals  of  apatit,  which  have  been  observed  by 
Manross,  in  1851.  The  mass  was  boiled  with  water  in  a  silver 
dish,  the  solution  contained,  besides  fluoride  of  sodium,  much 
phosphate  of  soda.  The  crystals  of  the  fluoride  were  skimmed 
off  during  evaporation,  and  purified  by  repeated  washing  and 
recrystallization.  An  analysis  showed  them  to  be  pure,  but  the 
yield  was  too  much  below  the  calculated  amount,  and  the  opera- 
tion too  tedious. 
An  alteration  of  the  mixture  to  CaO  +  2CaF  +  2NaO,  P05, 
thus  hoping  to  obtain  2NaF  and  3CaO,  P05,  had  a  rather 
less  favorable  result,  and  formed  the  same  crystals  of  apatit  : 
3  (3CaO,  P05)  -f  CaF.  To  obtain  this,  instead  of  phosphate 
of  lime,  an  addition  of  J  CaF  to  the  first  mixture  was  made, 
which,  however,  proved  to  be  only  a  little  more  favorable. 
Phosphate  of  potassa  substituted  for  the  soda  salt  yielded  so 
little  fluoride  of  potassium  that  it  could  not  be  obtained  pure. 
If  the  above  melted  mass,  instead  of  being  boiled,  is  extracted 
by  water  in  a  water  bath,  and  the  filtered  liquor  concentrated  in 
it,  on  cooling,  clear  crystals,  regular  octohedrons,  are  formed, 
which  are  hard,  and  of  a  nauseous  alkaline  taste;  their  spec, 
grav.  at  25°  C,  (77°  F.)  is  2.2165;  at  25°  C.  their  saturated 
solution  weighes  1.0329,  and  contains  1  part  of  the  salt  in  8.31 
water;  when  saturated  at  70° C.  (158°F.)  1  part  is  dissolved 
in  1.74  water,  and  has  a  spec.  grav.  of  1.1091.  The  analysis 
proved  it  to  be  of  the  following  composition:  3NaO,  P05  +  NaF 
+  24HO.  Boiling  of  the  solution  decomposes  it,  separating 
fluoride  of  sodium. 
The  same  salt  is  obtained  by  digesting  finely  pulverized  kryo- 
lith  of  Greenland,  (3NaF  +  Al2  F3)  in  a  solution  of  phosphate 
of  soda  with  caustic  soda ;  and  by  evaporating  a  mixture  of  the 
solutions  of  the  medicinal  phosphate  of  soda,  caustic  soda  and 
fluoride  of  sodium.     Soda,  in  this  double  salt,  cannot  be  sub- 
