78 THE ATOMIC WEIGHTS. 



FLUORmE. 



The* atomic weight of fluorine has been determined only 

 by one general method, namely, by the conversion of flu- 

 orides into sulphates. Excluding the early results of Davy,* 

 we have only to consider the experiments of Berzelius, 

 Louyet, Dumas, and DeLuca, with reference to the fluorides 

 of calcium, sodium, potassium, barium, and lead. 



The ratio between calcium fluoride and sulphate has been 

 determined by the four 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 ensure complete transforma- 

 tion special precautions are necessary ; such, for instance, as 

 repeated 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,t 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, zh .0004 



Louyet's researches^ were much more elaborate than the 

 foregoing. He began with a remarkably concordant series 

 of results upon fluor spar, in Avhich one gramme of the flu- 

 oride yielded from 1.734 to 1.737 of sulphate. At first he 

 regarded these as accurate, but he soon found that i)articles 

 of spar had been coated with sulphate, and had therefore 

 escaped action. In the following series this source of error 

 was jj-uarded against. 



*Phil. Trans., 1814,64. 



t Poggend. Annal., 8, i. 1826. 



X Ann. Chim. Phys., (3,) 25, 300. 1849. 



