Dispersion of Fluorbenzene and Allied Compounds. 7 





Per cent. 



»A' 



R H . 



Potassium fluoride 



3964 

 34-24 



8-15 



8-42 



8-38 

 8-70 







Mean value ... KP 



8-28 

 7-85; 



8-54 

 8-36 



K 



F 





0-43 



0-18 







Ammonium Fluoride. — The salt was prepared by saturating 

 ammonia with hydrofluoric acid and gently evaporating down 

 in vacuo. An aqueous solution containing 3 6* 88 per cent., 

 having a specific gravity of 1*1734 at 10°-7C.,gave indices for 

 A = 1-3689, for F = 1-3782, and for H = 1-3853. The mole- 

 cular refractions calculated from these are given below, and 

 the value of NH 4 is deducted : — 





E A . 



E F . 



E H . 



NH 4 F 



NH 4 



10-69 



10-26 



10-97 

 10-55 



11-16 

 10-81 



F 



0-43 



0-42 



0-35 



Hydrofluoric Acid. — Notwithstanding the difficulty of work- 

 ing with hydrofluoric acid, we succeeded in obtaining a de- 

 termination for the line D in an aqueous solution of this 

 substance. The strength was 23*2 per cent. ; the specific gravity 

 was 1*101 ; the refractive index was 1*3155 ; the molecular 

 refraction for D was therefore 2*64. Deducting 1*31 for the 

 hydrogen, we obtain E D =1*33 for the fluorine. This is a 

 somewhat larger figure than what is given by other com- 

 pounds ; but that is only in accordance with what occurs in 

 the case of the other halogen acids, which always give figures 

 in excess of theory. The length of the spectrum was evidently 

 very small, but no trustworthy measurements were made. 



Hydrofluo silicic Acid. — Different preparations of this acid in 

 aqueous solution gave rather discordant results. But the two 

 most trustworthy gave the following : — 



