108 NON-METALS AND THEIR COMBINATIONS. 



Fluorine, Fl = 19. This element is found in nature, chiefly 

 as fluorspar, calcium fluoride, CaFl 2 . Fluorine itself is scarcely 

 known in the elementary state, because it is very difficult to 

 obtain any material (from which a vessel might be made) which 

 is not chemically acted upon by fluorine. All metals, glass, 

 organic substances, etc., which have been used as vessels for 

 liberating fluorine were destroyed before satisfactory results 

 were obtained. Most likely, fluorine is a pale green gas, of 

 highly suffocating and poisonous properties. 



Hydrofluoric acid, HF1 (Hydrogen fluoride). A colorless gas, 

 very irritating, soluble in water. It is obtained by the action 

 of sulphuric acid on fluorspar: 



CaFl 2 + H 2 S0 4 = 2HF1 + CaS0 4 . 



Hydrofluoric acid, either in the gaseous state or its solution 

 in water, is used for etching on glass. This property is due to 

 the affinity which fluorine has for the constituents of glass, and 

 which are dissolved by it. 



QUESTIONS. 



161. How is bromine found in nature? 



162. State the physical and chemical properties of bromine. 



163. What is hydrobromic acid, and how can it be made? 



164. By what tests may bromine and bromides be recognized ? 



165. What is the chief source of iodine? 



166. What are the chemical and physical properties of iodine ? 



167. What is tincture of iodine, what is its color, and how does it 

 stain the skin ? 



168. Mention reactions by which iodine and iodides may be recog- 

 nized. 



169. By what element may bromine and iodine be liberated from 

 their compounds? 



170. How is hydrofluoric acid made, and what is it used for? 



