xii THE HALOGENS 235 



" That there exists in the fluoric compounds a peculiar 

 substance, possessed of strong attractions for metallic 

 bodies and hydrogen, . . . and which, in consequence of 

 its strong affinities and high decomposing agencies, it will 

 be very difficult to examine in a pure form, and, for the 

 sake of avoiding circumlocution, it may be denominated 

 FLUORINE, a name suggested to me by M. Ampere " 

 (Works, V. 423). 



Davy concluded further that : 



" Fluor spar and other analogous substances, . . . must 

 be regarded as binary compounds of metals, and fluorine" 

 ( Works, V. 424), and 



" That the pure liquid fluoric acid consists of hydrogen 

 united to a substance, which, from its strong powers of 

 combination, has not as yet been procured in a separate 

 form, but which is detached from hydrogen by metals" 

 (Works, V. 425). 



This acid, composed of hydrogen and fluorine, is now 

 known as HYDROFLUORIC ACID. 1 Davy made many attempts 

 to decompose the acid by the electric current, but did not 

 succeed in isolating fluorine. The element was, however, 

 prepared by this method by Moissan in 1886. 



B. IODINE. 



Iodine discovered by Courtois (1811). The view that 

 chlorine was an element was greatly strengthened by the 

 isolation, in 1811 (Hist. Acad. Sri., 1813, p. cxxiv), of a 

 substance which resembled chlorine in its properties, and 

 like chlorine could not be decomposed into simpler con- 

 stituents. 



1 This name was first suggested by Davy (Works, IV. 350) in 1812 

 to express the view that the liquid was a hydrated oxy-acid, but was 

 abandoned by him in the following year in favour of the older name 

 " fluoric acid." It was introduced again by Gay-Lussac, in 1814, to 

 express the fact that the acid contained, not water as Davy had suggested, 

 but hydrogen. 



