240 NON-METALS AND THEIR COMBINATIONS. 



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

 strong acid properties, easily soluble in water. 



Diluted hydrobromic avid, 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 1.076. 



Hydrobromic acid acts in nearly all respects like hydrochloric. It is less 

 stable, and less powerful oxidizing agents will liberate the bromine than are 

 required to liberate chlorine. Nearly all bromides are soluble in water, the 

 insoluble ones being those of silver, mercury (ous), and lead. Bromides are 

 mostly white. 



The ionic reactions for bromine compounds are analogous to those for chlo- 

 rine compounds. 



Hypobromous acid, HBrO ; Bromic acid, HBrO 3 , and their 

 salts, the hypobromites and bromates, are analogous to the corre- 

 sponding chlorine compounds, and may be obtained by analogous 

 processes. Oxides of bromine are not known. 



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 ammonia water. 



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

 bromine, which may be dissolved by shaking with carbon disulphide. 

 Excess of chlorine oxidizes bromine to colorless bromic acid. Hence, 

 it must be added cautiously, else a small quantity of bromine will 

 escape detection. The test is a delicate one. 



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

 yellow. The starch may be held in the vapor on the end of a rod. 



4. A solution of mercurous nitrate, or of lead acetate produces 

 a white precipitate of mercurous bromide, or lead bromide, both of 

 which are insoluble in water and dilute acids. 



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

 bromic acid, HBr, a portion of which decomposes with liberation of 

 yellowish-red vapors of bromine. See explanation above. 



Tests 2 and 5 combined with test 1 are decisive and sufficient to 

 recognize hydrobromic acid and its salts, and to distinguish them 

 from chlorides. 



Iodine, lodum, I = 125.90. Iodine is found in nature in com- 

 bination with sodium and potassium, in some spring waters and in 



