490 PRINCIPLES OF CHEMISTRY 



with, chlorine, and it was impossible to study the properties of the 

 resultant gas. Brauner (1881) also obtained fluorine by igniting cerium 

 fluoride, 2CeF 4 = 2CeF 3 + F 2 ; but this, like all preceding efforts, 

 only showed fluorine to be a gas which decomposes water, and is 

 capable of acting in a number of instances like chlorine, but gave no 

 possibility of testing its properties. It was evident that it was 

 necessary to avoid as far as possible the presence of water and a rise of 

 temperature ; this Moissan succeeded in doing in 1886. He decom- 

 posed anhydrous hydrofluoric acid, liquefied at a temperature of 23 

 and contained in a U-shaped tube (to which a small quantity of 

 potassium fluoride had been added to make it a better conductor), by 

 the action of a powerful electric current (twenty Bunsen's elements in 

 series). Hydrogen was then evolved at the negative pole, and fluorine 

 appeared at the positive pole (of iridium platinum) as a pale green gas 

 which decomposed water with the formation of ozone and hydrofluoric 

 acid, and combined directly with silicon (forming silicon fluoride, SiF 4 ), 

 boron (forming BF 3 ), sulphur, &c. Its density (H = 1) is 18, so that 

 its molecule is F 2 . But the action of fluorine on metals At the ordinary 

 temperature is comparatively feeble, because the metallic fluoride 

 formed coats the remaining mass of the metals ; it is, however, com- 

 pletely absorbed by iron. Hydrocarbons (such as naphtha), alcohol, 

 &c., immediately absorb fluorine, with the formation of hydrofluoric 

 acid. Fluorine when mixed with hydrogen can easily be made to 

 explode violently, forming hydrofluoric acid. 49 



In 1894, Brauner obtained fluorine directly by igniting the easily 



49 According to Moissan, fluorine is disengaged by the action of an electric current 

 on fused hydrogen potassium fluoride, KHF 2 . The present state of chemical knowledge 

 is such that the knowledge of the properties of an element is much more general than 

 the knowledge of the free element itself. It is useful and satisfactory to learn that 

 even fluorine in the free state has not succeeded in eluding experiment and research, 

 that the efforts to isolate it have been crowned with success, but the sum total of 

 chemical data concerning fluorine as an element gains but little by this achievement. The 

 gain will, however, be augmented if it be now possible to subject fluorine to a compara- 

 'tiye study in relation to oxygen and chlorine. There is particular interest in the pheno- 

 mena of the distribution of fluorine and oxygen, or fluorine and chlorine, competing under 

 different conditions 'and relations. We may add that Moissan (1892) found that free 

 fluorine decomposes H 2 S, HC1, HBr, CS 2 , and CNH with a flash ; it does not act upon 

 O 2 , N 2 , CO, and CO 2 ; Mg, Al, Ag, and Ni, when heated, burn in it, as also -do S, Se,P (forms 

 PF 5 ) ; it reacts upon H 2 even in the dark, with the evolution of 866'00 units of heat. At 

 a temperature of - 95, F 2 still retains its gaseous state. Soot and carbon in general (but 

 not the diamond) when heated in gaseous fluorine forin fluoride of carbon, CF 4 

 (Moissan, 1890) ; this compound is also formed at 800 by the double decomposition of 

 CC1 4 and AgF ; it is a gas which liquefies at 10 tinder a pressure of 5 atmospheres. 

 With an alcoholic solution of KHO, CF 4 gives K 2 CO 3 , according to the equation CF 4 + 6KHO 

 = K 2 CO 5 + 4KF + 8HaO. CF 4 is not soluble in water, but it is easily soluble in CC1 4 and 

 alcohol 



