124 NON-METALS AND THEIR COMBINATIONS. 



becomes readily decomposed with formation of sulphur dioxide and 

 free bromine. Thus : 



2NaBr -f H 2 SO 4 ; = 2HBr + Na 2 SO 4 ; 

 2HBr + H 2 S0 4 = = 2Br + SO 2 + 2H 2 O. 



If, however, dilute sulphuric acid is added to a warm solution of 

 potassium bromide, potassium sulphate is formed, a portion of which 

 crystallizes on cooling. From the remaining portion of the salt, the 

 hydrobromic acid may be separated by distillation. 



Hydrobromic acid may also be obtained by the formation of bromide of 

 phosphorus, PBr 5 (the two elements combine directly), and its decomposition 

 by water : 



PBr 5 + 4H 2 O = 5HBr + H 3 PO 4 . 



In the form of solution this acid may be prepared also by treating bromine 

 under water with hydrosulphuric acid until the brown color of bromine has 

 entirely disappeared. The reaction is as follows : 



lOBr + 2H 2 S -f- 4H 2 = lOHBr + H 2 SO 4 + S. 



The liquid is filtered from the sulphur and separated from the sulphuric acid 

 by distillation. 



Hydrobromic acid is, like hydrochloric acid, a colorless gas, of 

 strong acid properties, easily soluble in water. 



Diluted hydrobromic add, Acidum hydrobromicum dilutum, is a solu- 

 tion of 10 per cent, of hydrobromic acid in water. It is a colorless, 

 odorless, acid liquid of the specific gravity 1.077. 



Hypobromic acid, HBrO ; Bromic acid, HBrO 3 , and their salts, 

 the hypobromites and bromates, are analogous to the corresponding 

 chlorine compounds, and may be obtained by analogous processes. 



Tests for Bromides. 

 (Potassium bromide, KBr, may be used.) 



1. Silver nitrate produces in solutions of bromides a slightly yel- 

 lowish-white precipitate of silver bromide, insoluble in nitric acid, 

 sparingly soluble in ammonium hydroxide. 



2. Addition of chlorine water, or heating with nitric acid, liberates 

 bromine, which may be dissolved by shaking with chloroform or ether. 



3. Mucilage of starch added to the liberated bromine is colored 

 yellow. 



4. A crystal of potassium bromide dropped into an acidified solu- 

 tion of cupric sulphate produces a deep red-brown coloration of cupric 

 bromide, CuBr 2 . 



5. Strong sulphuric acid added to a dry bromide liberates hydro- 



