BORON AND FLUORINE. 



45 



tions. Comparisons by cross-reference have been advocated and 

 frequently been utilized by F. W. Clarke 9 and have often fur- 

 nished valuable data and checks upon experimental work. As a 

 rule, however, the original experimenter scarcely ever determines 

 a cross-ratio for its own sake. In most cases two compounds 

 may be brought into direct relation without the intervention of a 

 third. In some instances, however, such direct comparisons are 

 most unpromising, if not impossible, for practical reasons. For 

 such reasons, an indirect ratio, or cross-ratio, may be preferable 

 to a direct ratio. 



TABLE 3. 1 



1 Experimental data recorded in table 1 (p. 42.) 



In the determination of the atomic weight of fluorine, for 

 example, it would seem very desirable to establish its ratio to 

 another halogen. However, since the chemistry of the halides 

 holds forth no very promising means of comparing the fluoride 

 of a given element directly with another halide of the same ele- 

 ment, practically no efforts have been made in this direction. 

 True enough, the analyses of silver fluoride by Berzelius 10 and 

 possibly those by Fremy n would fall within the category; the 

 properties of silver fluoride, however, are such as to deprive these 

 analyses of any practical value in the fixing of the atomic weight 



A Recalculation of the Atomic Weights, 3d ed. (1910). 



10 Afhandlingar i Fys. Kemi Miner. 4, 243, 455 (1815). The original paper we have 



not seen. The reference is that given by Brauner (in Abegg's "Handbuch"). 

 The data are also given in Christensen's paper on the atomic weight of fluorine 

 (Jour. prak. Chem. (2) 35, 541-559 (1887). 



11 Ann. chim. phys. (3) 47, 1 (1856). 



