128 NON-METALS AND THEIR COMBINATIONS. 



and set in the open air for a few hours (heating slightly facilitates the action) ; 

 upon removing the wax or paraffin, the glass will be found to be etched where 

 its surface was exposed to the vapors of the acid. This experiment serves also 

 as the best test for 



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 recognized. 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 ? 



