FLUORINE. 277 



Gooch and Rowland's series, of which the mean gives Te = 125.96, a 

 value very little above that of iodine. 



In considering the experimental methods, reference may properly be 

 made to the controversy regarding the atomic weight of antimony. It 

 will be seen that Dexter, estimating the latter constant by the conver- 

 sion of the metal into Sb 2 4 , obtained a value approximately of Sb = 122. 

 Dumas, working with SbCl 3 , obtained nearly the same value. Schneider 

 and Cooke, on the other hand, have established an atomic weight for 

 antimony near 120, and Cooke in particular has traced out the constant 

 errors which lurked unsuspected in the work of Dumas. Now in their 

 physical aspects tellurium and antimony are quite similar. The oxida- 

 tion of tellurium to dioxide resembles in many particulars that of anti- 

 mony, and may lead to error in the same way. In each of the six tel- 

 lurium ratios there is still uncertainty, and a positive measurement, free 

 from objections, of the constant in question is yet to be made. 



FLUORINE. 



The atomic weight of fluorine has been chiefly determined by one 

 general method, namely, by the conversion of fluorides into sulphates. 

 The work of Christensen, however, is on different lines. Excluding the 

 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,f 

 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 

 I-75I 



Mean, 1.750, .0004 



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

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



* Phil. Trans., 1814, 64. 



f Poggend. Annalen, 8, i. 1826. 



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



