44  RESEARCHES  ON  THE  DIFFUSION  OF  FLUORINE. 
6.  The  river  "water  in  France  richest  in  fluorides,  is  that  of  the 
Somme,  taken  at  Amiens. 
7.  The  various  mineral  waters  are  not  equally  rich  in  fluorides ; 
the  richest  of  those  which  I  have  examined,  are :  the  water  of 
Oontrexe'ville,  Antogast,  and  Chatenois  (Bas-Rhin). 
One  litre  of  these  waters  is  sufficient  for  giving  unequivocal 
marks  of  the  presence  of  fluorine. 
8.  On  the  contrary,  sea  water  (Atlantic)  contains  it  only  in 
proportions  detectable  in  300  litres.  This  fact  establishes  a  very 
decided  difference  between  this  water  and  the  mineral  waters 
which  are  analogous  to  sea  water. 
9.  The  law  of  the  diffusion  of  fluorine  in  the  earth's  crust 
may  be  formulised  thus  :  there  is  fluoride  of  calcium  in  all  the 
waters  which  contain  bicarbonate  of  lime ;  there  may  also  be 
fluorine  in  the  rocks  and  minerals  which  are  formed  by  the  way 
of  sediment. 
With  regard  to  the  manner  of  putting  these  facts  in  evidence, 
it  results  from  what  is  said  in  the  memoir,  that : — 
10.  The  classical  process  sins  in  two  especial  points,  and  leads 
us  to  admit  the  existence  of  fluorine  where  there  is  none  ;  this  is 
owing : — 
A.  To  the  action  which  sulphuric  acid  may  exert  on  the  glass 
plate. 
B.  To  small  quantities  of  hydrofluoric  acid  which  this  acid 
may  contain. 
11.  I  eliminate  these  causes  of  error  : — 
A.  By  replacing  the  glass  plate  by  a  place  of  rock  crystal. 
B.  By  employing  an  acid  free  from  hydrofluoric  acid. 
12.  The  acid  employed  by  preference  for  decomposing  the 
fluorides,  is  sulphuric  acid  purified  by  diluting  it  with  water,  and 
exposing  it  for  some  time  to  a  temperature  of  150°  to  180° 
(302°  to  358°  F.) 
13.  The  solvent  which  I  employ  is  hydrochloric  acid,  which, 
with  some  care,  may  be  found  free  from  fluorine  in  com- 
merce. 
My  memoir  makes  known  the  circumstances  in  which  such 
hydrochloric  acid  is  produced  in  the  large  way. 
14.  All  the  estimates  of  fluorine  heretofore  made  with  the  aid  , 
of  sulphuric  acid,  should  be  repeated. 
