404 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 54 



FLUOEINE. 



The atomic weight of fluorine has been commonly determined by two 

 general methods; namely, the conversion of fluorides into sulphates. 

 There are, however, two exceptions, which will be considered in due 

 time. 



Excluding tlie early results of Davy/ we have to consider first the 

 experiments of Berzelius, Louyet, Dumas, De Luca and Moissan with 

 reference to the fluorides of calcium, sodium, potassium, barium and lead. 



The ratio between calcium fluoride and sulphate has been determined 

 by the five investigators above named, and by one general process. The 

 fluoride is treated with strong sulphuric acid, the resulting sulphate is 

 ignited, and the product weighed. In order to insure complete trans- 

 formation special precautions are necessary, such, for instance, as re- 

 peated treatment with sulphuric acid, and so on. For details like these 

 the original papers must be consulted. 



The first experiments in chronological order are those of Berzelius,' 

 who operated upon an artificial calcium fluoride. He found, in three 

 experiments, for one part of fluoride the following of sulphate : 



1.749 

 1.750 

 1.751 



Mean, 1.750, ± .0004 



Hence F = 18.85. 



Louyet's researches ' were much more elaborate than the foregoing. 

 He began with a remarkably concordant series of results upon fluor spar, 

 in which one gramme of the fluoride yielded from 1.734 to 1.737 of 

 sulphate. At first he regarded these as accurate, but he soon found 

 that particles of spar had been coated with sulphate, and had therefore 

 escaped action. In the following series this source of error was guarded 

 against. 



Starting with fluor spar, Louyet found of sulphate as follows : 



1.742 



1.744 



1.745 



1.744 



1.7435 



1.7435 



Mean, 1.7437, ± .0003 



Hence F = 18.99. 



>■ PhiL Trans., 64. ]814. 



^ Poggend. .■Vnnalen, 8, 1. 1S26. 



= Ann. ChiiTi. Pliys. (3), 2.5, 300. 1849. 



