IODINE. 107 



sulphuric) acid. The liberated iodine distils, and is collected 

 in cooled receivers. 



Iodine is a heavy, bluish-black, crystalline substance of a 

 somewhat metallic lustre, a distinctive odor, a sharp and acrid 

 taste, and a neutral reaction. It fuses at 114, and boils at 180, 

 being converted into beautiful purple vapors, but it is also vola- 

 tilized at ordinary temperature in small quantities. It is spar- 

 ingly soluble in water, more soluble in water containing certain 

 salts, for instance potassium iodide; it is soluble in 11 parts of 

 alcohol (tincture of iodine), very soluble in ether, bisulphide of 

 carbon, and chloroform. The solution of iodine in alcohol or 

 ether has a brown, the solution in bisulphide of carbon or in 

 chloroform a violet color. Iodine stains the skin brown, and 

 when taken internally acts as an irritant poison. 



Hydriodic acid, Hydrogen iodide, HI. This is a colorless gas, 

 readily soluble in water; the solution is unstable, being easily 

 decomposed with liberation of iodine. 



"Whilst not of much importance itself, many of its salts, the 

 iodides, are of great interest. 



Tests for iodine and iodides. 



1. Add to free iodine (or to an iodide, after it has been de- 

 composed by a few drops of chlorine water) mucilage of starch: 

 a dark blue color is produced, due to the formation of " blue 

 iodized starch." 



2. Liberate from solution of an iodide the iodine by chlorine 

 water, and shake the solution with bisulphide of carbon or 

 chloroform. After standing a few minutes the liquids form a 

 layer of a beautiful violet color. 



3. Add to solution of an iodide, solution of silver nitrate : a 

 pale yellow precipitate of silver iodide, Agl, falls, which is in- 

 soluble in nitric acid, and sparingly soluble in dilute ammonium 

 hydrate. 



4. Add lead acetate to a neutral solution of an iodide : a 

 yellow precipitate of lead iodide, PbI 2 , is produced. 



5. Add mercuric chloride to a neutral solution of an iodide : 

 a red precipitate of mercuric iodide, HgI 2 , is produced. 



