BR OMINE IODINE FL UORINE. 125 



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

 yellowish-red vapors of bromine. See explanation above. 



Iodine, lodum, I = 126.53. Iodine is found in nature in com- 

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

 sea-water, from which latter it is taken up by sea-plants and many 

 aquatic animals. Iodine is derived chiefly from the ashes of sea- 

 weeds known as Mp. By washing these ashes with water, the soluble 

 constituents are dissolved, the larger quantities of sodium chloride, 

 sodium and potassium carbonates are removed by evaporation and 

 crystallization, and from the remaining mother-liquor iodine is ob- 

 tained by treating the liquor with manganese dioxide and hydro- 

 chloric (or sulphuric) acid : 



2KI + Mn0 2 + 2H 2 S0 4 = K 2 SO 4 -f MnSO, + 2H 2 O + 21. 



The liberated iodine distils, and is collected in cooled receivers. 

 Sodium nitrate found in Chili contains a small quantity of sodium 

 iodate, and the mother-liquors, from which the nitrate has been crys- 

 tallized, contain enough iodate to be employed for the preparation of 

 iodine. 



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

 metallic lustre, a distinctive odor, a sharp and acrid taste, and a neu- 

 tral reaction. Specific gravity 4.948 at 17 C. (62.6 F.). It fuses 

 at 114 C. (237 F.), and boils at 180 C. (356 F.), being converted 

 into beautiful purple- violet vapors ; also, it volatilizes in small quanti- 

 ties at ordinary temperature. It is soluble in about 5000 parts of 

 water, more soluble in water containing salts, for instance, potassium 

 iodide; it is soluble in 10 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 disulphide 

 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 decom- 

 posed with liberation of iodine. It may be obtained by processes 

 analogous to those mentioned for the preparation of hydrobromic 

 acid. The action of hydrosulphuric acid upon iodine in the presence 

 of water is as follows : 



H 2 S + 21 : 2HI + S. 



Another method depends on the decomposition of an aqueous so- 

 lution of potassium iodide by an alcoholic solution of tartaric acid. 



